Tektronix 577, 576, 177 Service and user manual

Download

Page 1

PLEASE CHECK FOR CHANGE INFORMATION AT THE REAR OF THIS MANUAL.

576 CURVE-TRACER

INSTRUCTION MANUAL

Tektronix, Inc. P.O. Box 500 Beaverton, Oregon 97077 070-0905-01 Product Group 48

Serial Number _

First Printing NOV 1970 Revised APR 1988

Page 2

Products of Tektronix, Inc. and its subsidiaries are covered by U.S. and foreign patents and/or pending patents.

TEKTRONIX, TEK, SCOPE-MOBILE, and are registered trademarks of Tektronix, Inc. TELEQUIPMENT is a registered trademark of Tektronix U.K. Limited.

Printed in U.S.A. Specification and price change privileges are reserved.

INSTRUMENT SERIAL NUMBERS

Each instrument has a serial number on a panel insert, tag, or stamped on the chassis. The first number or letter designates the country of manufacture. The last five digits of the serial number are assigned sequentially and are unique to each instrument. Those manufactured in the United States have six unique digits. The country of manufacture is identified as follows:

B000000	Tektronix, Inc., Beaverton, Oregon, USA
100000	Tektronix Guernsey, Ltd., Channel Islands
200000	Tektronix United Kingdom, Ltd., London
300000	Sony/Tektronix, Japan
700000	Tektronix Holland, NV, Heerenveen,
	The Netherlands

Page 3

		-
Section 1	SPECIFICATION
	Electrical Characteristics	1-1
	Environmental Characteristics	1-5
	Mechanical Characteristics	1-5
Section 2	OPERATING INSTRUCTIONS
	Initial Considerations	2-1
	Controls, Connectors, and Readout	2-3
	Precautions	2-7
	General Description of Instrument
	Operation	2-7
	First Time Operation	2-8
	General Operating Information	2-1
	Applications	2-2
	Section 1 Section 2	Section 1 SPECIFICATION Electrical Characteristics Environmental Characteristics Mechanical Characteristics Mechanical Characteristics Section 2 OPERATING INSTRUCTIONS Initial Considerations Controls, Connectors, and Readout Precautions General Description of Instrument Operation First Time Operation First Time Operation Applications

WARNING

Section 3 CIRCUIT DESCRIPTION Block Diagram Description ...... 3-1 Circuit Description ....................................

Section 4 MAINTENANCE

Preventive Maintenance	4-1
Troubleshooting	4-1
Corrective Maintenance	4-9
Obtaining Replacement Parts	4-9
Component Removal and
Replacement	4-1(
Test Fixture Interface	4-1
Circuit Board Pictures	4-23

age

Page

Section 5	PERFORMANCE CHECK/ CALIBRATION
	General	5-1
	Preliminary Calibration Procedure	5-3
	Preliminary Performance Check Procedure	5-3
	Performance Check/Calibration Record and Index (Table 5-2)	5-3
	Performance Check/Calibration Procedure	5-4
Appendix A	Alternate Calibration Procedure	. A-1

Section 6 ELECTRICAL PARTS LIST

Section 7 MECHANICAL PARTS LIST

Section 8 DIAGRAMS

General Information	8-1
	8-2
Waveform and Voltage Test Conditions	8-3
Block Diagram
Circuit Diagrams

CHANGE INFORMATION

Abbreviations and symbols used in this manual are based on or taken directly from IEEE Standard 260 "Standard Symbols for Units", MIL-STD-12B and other standards of the electronics industry.

Page 4

OPERATORS SAFETY SUMMARY

The general safety information in this part of the summary is for both operating and servicing personnel. Specific warnings and cautions will be found throughout the manual where they apply, but may not appear in this summary.

TERMS

In This Manual

CAUTION statements identify conditions or practices that could result in damage to the equipment or other property.

WARNING statements identify conditions or practices that could result in personal injury or loss of life.

As Marked on Equipment

CAUTION indicates a personal injury hazard not immediately accessible as one reads the marking, or a hazard to property including the equipment itself.

DANGER indicates a personal injury hazard immediately accessible as one reads the marking.

SYMBOLS

In This Manual

This symbol indictes where applicable cautionary or other information is to be found.

As Marked on Equipment

Protective ground (earth) terminal

DANGER --- High voltage

ATTENTION — refer to manual.

Power Source

This product is intended to operate from a power module connected to a power source that will not apply more than 250 volts rms between the supply conductors or between either supply conductor and ground. A protective ground connection by way of the grounding conductor in the power cord is essential for safe operation.

Grounding the Product

This product is grounded through the grounding conductor of the power module power cord. To avoid electrical shock, plug the power cord into a properly wired receptacle before connecting to the product input or output terminals. A protective ground connection by way of the grounding conductor in the power module power cord is essential for safe operation.

Danger Arising From Loss of Ground

Upon loss of the protective-ground connection, all accessible conductive parts (including knobs and controls that may appear to be insulating) can render an electric shock.

Use the Proper Fuse

To avoid fire hazard, use only the fuse of correct type, voltage rating and current rating as specified in the parts list for your product.

Refer fuse replacement to qualified service personnel.

Do Not Operate in Explosive Atmospheres

To avoid explosion, do not operate this product in an explosive atmosphere unless it has been specifically certified for such operation.

Do Not Operate Without Covers

To avoid personal injury, do not operate this product without covers or panels installed. Do not apply power to the plug-in via a plug-in extender.

Page 5

SERVICING SAFETY SUMMARY

FOR QUALIFIED SERVICE PERSONNEL ONLY

Refer also to the preceding Operators Safety Summary.

Do Not Service Alone

Do not perform internal service or adjustment of this product unless another person capable of rendering first aid and resuscitation is present.

Use Care When Servicing With Power On

Dangerous voltages exist at several points in this product. To avoid personal injury, do not touch exposed connections or components while power is on.

Disconnect power before removing protective panels, soldering, or replacing components.

Power Source

This product is intended to operate from a power source that does not apply more than 250 volts rms between the supply conductors or between either supply conductor and ground. A protective ground connection by way of the grounding conductor in the power cord is essential for safe operation.

ADD JAN 1984

Page 6

Page 7

WARNING NOTICE

Your 576 or 577/177 is designed to be a very versatile and flexible characteristic curve tracer capable of testing both high voltage and high current devices. The 576 collector supply can generate peak voltages up to 1500 volts, the 577/177 up to 1600 volts, and both are capable of generating up to 20 amps at lower voltages. This wide range of voltage and current makes it possible for you to test a very wide range of devices. However, these supplies are potentially very dangerous.

It has come to our attention that it is becoming increasingly common for our customers to connect 576's and 577/177's to devices or fixturing external to the instrument and thus external to or outside of the safety features that are designed into the instruments.

We have provided a wide range of adapters that are designed to allow you to test your devices while inside the plastic protective cover. However, if you feel it is necessary to connect the collector supply to devices or fixturing outside of this protective cover, in effect defeating the built-in safety features of the instrument, the following simple modification will at least allow you to do so with the plastic protective cover still installed. This will reduce the chances of the operator coming into contact with the collector supply voltage.

This simple modification will prevent exposed contacts at the instrument's test fixture. This prevents operators from exposure to dangerous voltages only at the curve tracer end of the external wires. Exposure to dangerous voltage is still possible at the external fixture connections and the DUT. If external wires/fixturing are used by your organization, then it is your responsibility to ensure that the necessary safeguards (additional protective cover, interlocks, etc.) to protect the operators are provided.

Modification

Drill a hole or otherwise remove just enough material from one of the sides of the plastic protective cover as shown on the attached drawing, to allow the necessary leads to be brought out through the side of the cover.

If you have misplaced or damaged the plastic protective cover, order a replacement through your local Tektronix Field Office, for the plastic protective cover is an integral part of the safety features for these instruments.

A plastic protective cover that has been modified (notched) is available from Tektronix by ordering part number 337-1194-02.

WARNING

DANGEROUS VOLTAGE MAY STILL BE EXPOSED AT THE DEVICE OR FIXTURE END OF THE CABLES WHICH YOU BRING OUT OF THE PLASTIC PROTECTIVE COVER. IT IS YOUR RESPONSIBLITY TO PROVIDE SAFEGUARDS TO PROTECT THE OPERATOR AT THE CABLES END.

Page 8

Page 9

COVER MODIFICATION

Drill a hole, notch or otherwise remove just enough material, from the left side of the plastic protective cover box (as shown in Fig. A) to allow test leads to be brought out through the cover. This will allow the cover to be kept in place while using outside test fixtures.

PROTECTIVE COVER "NOTCHED" TO ALLOW TEST LEADS TO BE BROUGHT OUT THROUGH THE COVER WHILE LEAV-ING THE COVER IN PLACE.

Page 10

Page 11

NOTICE

To increase the operator safety of the 577/177 products, the RED button that was located on the front of the 177 has been removed. All references to the red button in either the Operators or Service manuals are no longer valid.

If your instrument still has the red interlock bypass button located on the front left side of the 177, it is strongly recommended that you contact your nearest Tektronix Field Office to schedule the installation of the Safety Interlock Modification.

Page 12

Page 13

SECTION 1 SPECIFICATION

The Type 576 Curve Tracer is a dynamic semiconductor tester which allows display and measurement of characteristic curves of a variety of two and three terminal devices including bipolar transistors, field effect transistors, MOS-FETs, silicon controlled rectifiers and unijunction transistors. A variety of possible measurements is available using either grounded emitter or grounded base configurations. The instrument has available either an AC or a DC collector supply voltage ranging from 0 to ±1500 volts. The step generator produces either current or voltage steps, which may be applied to either the base terminal or the emitter terminal of the device under test. Step generator outputs range from 5 nA to 2 A in the current mode, and from 5 mV to 40 V in the voltage mode. The steps may also be produced as short duration pulses. Calibrated step offset allows offsetting the step generator output either positive or negative. The vertical display amplifier measures either collector current or leakage current with a maximum deflection factor of 1 nA/division when making a leakage

TABLE 1-1 ELECTRICAL CHARACTERISTICS

Collector Supply
Characteristic	Performance
Sweep Modes	Normal mode: AC (at line fre- quency); positive-or negative-going full wave rectified AC. DC mode: positive or negative DC.
DC Mode Ripple	No-load: 2% or less of voltage, or 0.1% or less of full range voltage.
Voltages Accuracy	Peak open circuit voltages on all ranges within +35% and -5%.

¹Collector Supply Maximum Continuous Peak Current Operating Time vs Duty Cycle and Ambient Temperature. With the PEAK POWER WATTS at 50 only, the following limitations apply: Maximum continuous operating time at rated current (100% duty cycle) into a short circuit is 20 minutes at 25 °C ambient, or 10 minutes at 40 °C ambient. Alternatively, duty cycle may be limited to 50% at 25 °C ambient or 25% at 40 °C ambient. (A normal family of curves for a transistor will produce a duty cycle effect to 50% or less even if operated continuously.) Over dissipation of the collector supply will temporarily shut it off and turn on the yellow COLLECTOR SUPPLY VOLTAGE DISABLED light. No damage will result.

measurement. The horizontal display amplifier allows measurement of both collector and base voltage.

The following electrical and environmental characteristics are valid for instruments operated at an ambient temperature of from +10°C to +40°C after an initial warmup period of 5 minutes, when previously calibrated at a temperature of +25°C ±5°C. Section 5, Performance Check and Calibration Procedure, gives a procedure for checking and adjusting the Type 576 with respect to the following specification.

The Type 576 MOD 301W is a standard Type 576 without the Readout Assembly. All the information contained in this manual pertaining to the Readout Assembly and its operation should be disregarded when used in conjunction with a modified instrument.


Ranges	15 V	75 V	350 V	1500 V
Maximum Peak Current (Normal Mode) ¹	10 A	2 A	0.5 A	0.1 A
Peak Current (Step Generator in Pulsed Steps Mode)	At least 20 A	At least 4 A	At least 1 A	At least 0.2 A
Minimum Series Resistance	0.3 Ω	6.5 Ω	140 Ω	3 kΩ
Maximum Series Resistance	6 5 kΩ	1.4 MΩ	6.5 MΩ	6.5 MΩ
Series Resistance Available	0.3 Ω, 1.4 Ω, 6.5 Ω, 30 Ω, 140 650 Ω, 3 kΩ, 14 kΩ, 65 kΩ, 3 kΩ, 1.4 MΩ and 6.5 MΩ, all wit 5% or 0.1 Ω.
Peak Power Watts Settings	0.1 W, 0.5 W, 2.2 W, 10 W, 50 and 220 W. Derived from nom peak open circuit collector volta and nominal series resistance val at nominal line voltage.			W, 50 W n nominal or voltages nce values
Safety Interlock	When M set to ei tective test ter	IAX PEA ither 75, box mu minals ar	K VOLT 350 or 15 st be in nd its lid	S switch is 500, a pro- place over closed be-

Page 14

Specification—Type 576

	fore voltage can be applied. Amber light on indicates interlock is open Bed light on indicates voltage is be-	Ripple Plus Noise	0.5% or less of AMPLITUDE switch setting or 1 nA, peak to peak.
Looping Compensation	ing applied to test terminals. Cancels stray capacitance between collector test terminal and ground	Voltage Mode AMPLITUDE Switch Range	50 mV to 2 V, in 1-2-5 sequence.
	in Standard Test Fixture and all Standard Test Fixture Accessories. Step Generator	Maximum Voltage (Steps and Aiding Offset)	20 times AMPLITUDE switch set- ting.
Accuracy (Current or Voltage Steps, Includ- ing Offset)		Maximum Current (Steps and Aiding Offset)	At least 2 A at 10 V or less, de- creasing linearly to 10 mA at 40 V.
Incremental Accuracy	Within 5% between any two steps, without .1X STEP MULT button pressed; within 10% with .1X STEP MULT button pressed.	Short Circuit Cur- rent Limiting (Steps and Aiding Offset)	20 mA, 100 mA, 500 mA, +100%- 0%; 2 A +50%-0%; as selected by CURRENT LIMIT switch.
Absolute Accuracy	Within 2% of total output, includ- ing any amount of offset, or 1% of AMPLITUDE switch setting, which-	Maximum Opposing Offset Voltage	10 times AMPLITUDE switch set- ing.
Step (Current or	One times or 0.1 times (with .1X	Maximum Opposing Current	Limited at between 5 mA and 20 mA
	AMPLITUDE switch setting.	Ripple Plus Noise	0.5% or less of AMPLITUDE switch setting, or 2 mV, peak to peak.
OFFSET MULT Con- trol Range	Continuously variable from 0 to 10 times AMPLITUDE switch setting, either aiding or opposing the step generator polarity.	Step Rates	(Front panel RATE button labels in parentheses.) 1 times (.5X), 2 times (NORM) and 4 times (2X) line fre-
Current Mode AMPLITUDE Switch Range Maximum Current (Steps and Aiding	200 mA to 50 nA, in 1-2-5 se- quence. 20 times AMPLITUDE switch set- ting, except 10 times switch setting		quency. Steps occur at zero collec- tor voltage when .5X or NORM RATE buttons are pressed, and also at peak voltage when 2X RATE button is pressed. Steps occur at collector voltage peak and at
Offset)*	when switch is set to 200 mA, and 15 times switch setting when the switch is set to 100 mA.		RATE buttons are pressed together.
Maximum Voltage (Steps and Aiding Offset)	At least 10 V.	Pulsed Steps	Pulsed steps 80 µs wide within +20%, -5% or 300 µs wide within +5%, -15% produced whenever one
Maximum Opposing Offset Current	Whichever is less: 10 times AMPLI- TUDE switch setting, or between 10 mA and 20 mA.		of the PULSED STEPS buttons is pressed. Pulsed steps can be pro- duced only at normal and .5 times normal rates. Collector Supply
Maximum Opposing	Between 1 V and 3 V.		mode automatically becomes DC when either the 300 µs or 80 µs
² Continuous DC Output continuous DC output c to 30°C ambient. Betwee DC operation should be duty cycle or less. A fam step) will automatically r ted continuously. Excee	vs Time, Temperature and Duty Cycle. 2A an be achieved for an unlimited period up en 30°C and 40°C ambient, 2A continuous limited to 15 minutes or limited to a 50% ily of steps (such as 10 steps at 200 mA per educe the duty cycle to 50% even if genera- eding the rating will temporarily shut off ument but no damage will result		PULSED STEPS button is pressed unless POLARITY switch is set to AC. If the 300 µs and 80 µs PULSED STEPS buttons are pressed together, 300 µs pulsed steps are produced, but collector supply mode does not change.

REV. D, JULY, 1975

Page 15

Specification-Type 576

							•
Steps and OffsetCorresponds with collector supplyPolaritypolarity (positive going when PO- LARITY switch is set to AC) when the POLARITY INVERT button is		tor supply when PO- AC) when button is	External Hori- zontal (Through Interface)	2%	3%	4%	3%
	released ply pol when	d. Is opp arity (ne either th	osite coll egative-go ne POLA	ector sup- ing in AC) RITY IN-	Leakage Collector Supply Mode
	VERT Lead Se GROU switch ED, P(	button elector sv NDED. is set to DLARITY	is presse witch is se If Leac BASE ( Y INVEF	ed or the t to BASE I Selector GROUND- T button	Vertical Emitter Current (VERT- ICAL Switch set between 10 nA and 2 mA)	2% ±1 nA	3% ±1 nA	4% ±1 nA	3% ±1 nA
Step Families	has no effect on steps and offset polarity. Repetitive families of characteristic curves generated with REP STEP E AMULY, button, pressed. Sinch		and onset aracteristic REP STEP ed. Single	Vertical Emitter Current (VERT- ICAL Switch set to 5 nA, 2 nA or 1 nA)	Not	Applicab	e	5% ±1nA
	family erated FAMIL	of charac each tir Y button	cteristic c ne SING n is presse	urves gen- LE STEP d.	Horizontal Collector or Base Volts
Number of Steps	Ranges from 1 to 10 as selected by the NUMBER OF STEPS switch. For zero steps, press SINGLE STEP EAMILY button		elected by PS switch. GLE STEP	VERTICAL switch set to: 1 μA or more	e 2%	3%	4%	3%
D	isplay Am	plifiers			100 nA, 10 nA or 1 nA	Not Ap	plicable		3% plu 0.025 \ for eac
Visplay Accuracies Display magnified (DIS- % of Highest On- creen Value) Display magnified (DIS- PLAY OFFSET Selec- tor switch set to either VERT X10 or HORIZ X10) and offset be-		d (DIS- Selec- either HORIZ set be-	Display Unmag- nified					vertica divisiono deflection on th CRT
	100 and 40 divi- sions	35 and 15 divi- sions	10 and 0 divi- sions		500 nA, 50 nA or 5 nA	Not Ap	plicable		3% plu 0.125 \ for each
Normal and DC Collector Supply Modes									division o deflection on the CRT
Vertical Col- lector Current	2%	3%	4%	3%	200 nA, 20 nA or 2 nA	Not Ap	plicable		3% plu 0.050 \
External Vert- ical (Through Interface)	2%	3%	4%	3%					for each vertica division o deflection
Horizontal Col- lector Volts	2%	3%	4%	3%					of the CRT
Horizontal Base Volts	2%	3%	4%	3%	Step Generator Display

Contraction of the

the state

and a second

1000

Contraction of the

Page 16

Specification—Type 576


Vertical Step Generator	3%	4%	5%	4%
Horizontal Step Generator	3%	4%	5%	4%
Deflection Factors Vertical Collector Current	1 μΑ/c 1-2-5 se	livision t	o 2 A/d	ivision in
Emitter Current	1 nA/d 1-2-5 se	1 nA/division to 2 mA/division in 1-2-5 sequence.
Step Generator	1 step/d	livision.
Horizontal Collector Volts	50 mV in 1-2-5	/division sequence	to 200 V	//division
Base Volts	50 mV 1-2-5 se	/division quence.	to 2 V/d	livision in
Input Imped- ance	At least 100 MΩ with HORIZON- TAL switch set to 50 mV, 100 mV and 200 mV BASE; 1 MΩ within 2% with switch set to .5 V, 1 V and 2 V
Step Generator	1 step/o	division
Maximum Displayed Noise	1% or less, or the following depend- ing on setting of MAX PEAK VOLTS switch:
	15	75	350	1500
Vertical				27 - 04
COLLECTOR	1μΑ	1 μΑ	2 μΑ	5 μΑ
EMITTER	1 nA	1 nA	2 nA	5 nA
Horizontal
COLLECTOR	5 mV	5 mV	20 mV	200 mV
Calibration Check	With [ switch deflect ically a whenew sed.	DISPLAY set to NC ed 10 d and horizo ver the C	OFFSE ORM (OF ivisions I ontally w AL butto	Γ Selector F), spot is both vert- ithin 1.5% on is pres-
	With [ switch (either within ly set	DISPLAY set to axis) the 0.5% of to CRT	OFFSE X10 MA e calibrat zero spot graticu	T Selector AGNIFIER ion spot is (previous le center)

	least 5 divisions for each coarse pos- ition.
Display Offset	Vertical or Horizontal offset of dis- play centerline value up to 10 divis- ions in 21 half division steps.
Display Positioning Accuracy Using POLARITY Switch	Spot positioning POLARITY swi AC position as 0.1 division of:	g with change in tch setting (using reference), within
	Vertically	Horizontally
AC	Centered	Centered
+(NPN)	-5 divisions	-5 divisions
-(PNP)	+5 divisions	+5 divisions
С	RT and Readout
CBT
Туре	Electrostatic defl	ection.
Screen Size	Calibrated area of 10 divisions by 10 divisions; 12 usable divisions horizontally (1 division equals 1 cm).
Typical Accel- lerating Poten- tial	4000 V
Readouts	Automatic digita Readout is autor readings would k able ranges or wo display.	Ily lighted display. natically blanked if be outside the avail- ould give erroneous
PER VERT DIV	1 nA to 20 A calculated from VER- TICAL switch setting, DISPLAY OFFSET Selector switch setting and MODE switch setting (or X10 Vertical Interface Input).
PER HORIZ DIV	5 mV to 200 V calculated from HORIZONTAL switch setting and DISPLAY OFFSET Selector switch setting.
PER STEPS	5 nA to 2A and culated from Al setting and .1X ton position (or Input).	5 mV to 20 V cal- MPLITUDE switch STEP MULT but- X10 Step Interface

Coarse positioning in 5 division in-

ontal Position Controls crements within 0.1 division; con-

Vertical and Horiz-

Page 17


	β or g _m PER DIV	1 μ to 500 k ca TICAL switch	Iculated from VER-
		OFESET Selec	tor switch setting
		AMPLITUDE	witch setting 1X
		STEP MULT b	utton position X10
		Vertical Interfa	ce Input and X10
		Step Interface In	nput.

1 6	Ροι	wer Requirements
	Power Connection	This instrumen	t is designed for
		operation from	power source with
		its neutral at or	near ground (earth)
		potential. It is	not intended for
			tom or across logs
		of single-phase,	three wire system.
		It is provided	with a three-wire
		power cord w	vith three-terminal
		polarized plug	for connection to
		the power sou	rce. Third wire is
		directly connect	ted to instrument
- 10gr -		frame, and is i	ntended to ground
		the instrument	to protect operating
		personnel, as	recommended by
		codes.	The first offer safety
			0001/40
	Line Voltage Ranges	TI5 VAC	230 VAC
	Low	90 V to 110 V	180 V to 220 V
	Medium	104 V to 126 V	208 V to 252 V
		112 V to 136 V	224 V to 272 V
	Line Frequency Range	48 to 66 Hz
_	Maximum Power	305 W, 3.2 A
	Consumption at 115
	VAC, 60 Hz
	ENVIRONME	Table 1-2 NTAL CHARACT	TERISTICS

Characteristic	Information
Temperature
Nonoperating	-40°C to +65°C

Specification-Type 576

Useful Operation	0°C to +50°C
Specified Operation	+10°C to +40°C
Altitude
Nonoperating	To 50,000 feet
Operating	To 10,000 feet
Vibration
Operating	15 minutes along each axis at 0.015 inch with frequency varied from 10-50-10 c/s in 1-minute cycles. Three minutes at any resonant point or at 50 c/s.
Shock
Nonoperating	30 g's, 1/2 sine, 11 ms duration, 1 shock per axis. Total of 6 shocks
Transportation	12 inch package drop. Qualified un- der the National Safe Transit Com- mittee test procedure 1A.

TABLE 1-3 MECHANICAL CHARACTERISTICS

Characteristic	Description
Dimensions
Height	≈15 inches
Width	≈11 3/4 inches
Depth	≈23 1/4 inches
Weight	≈69 lbs.
Finish
Front Panel (Type 576 and Standard Test Fixture)	Anodized Aluminum
Cabinet	Blue vinyl painted aluminum
Trim and Rear Panel	Satin finished chrome

Page 18

NOTES

	1
	1

	2
	2





	1

Page 19

SECTION 2 OPERATING INSTRUCTIONS

Change information, if any, affecting this section will be found at the rear of the manual.

The Type 576 is considered safe as shipped. Any modification of the interlock system in order to override its purpose of protecting operators from dangerous voltages, will make operation of the instrument potentially hazardous. Operators of the instrument should always be aware of the fact that when the red light is on dangerous voltages may appear at the Collector terminals.

General

This section of the instruction manual provides information necessary for operating the Type 576 and for using it to test various semiconductor devices. Included are setup procedures, a description of the Type 576 controls and connectors, a discussion of the theory of the instrument, a first time operation procedure, and general operating information. Also included is a section describing the use of the Type 576 for measuring the characteristics of various semi-conductor devices.

INITIAL CONSIDERATIONS

Cooling

The Type 576 maintains a safe operating temperature when operated in an ambient temperature between 0°C (32°F) and 50°C (122°F). Adequate clearance on all sides of the instrument should be provided to assure free air flow and dissipation of heat away from the instrument. A thermal cutout in the instrument provides thermal protection by disconnecting the power to the instrument if the internal temperature exceeds a safe operating level. Power is automatically restored when the temperature returns to a safe level. It should be noted that the instrument will turn off under certain conditions of high collector supply current output or high step generator current output even though the instrument is being operated in an ambient temperature which is within the specified range. See foot notes in the Specification section for further information

Operating Voltage and Frequency

The Type 576 can be operated from either a 115-volt or a 230-volt line voltage source. The LINE VOLTAGE SELECTOR assembly, located on the rear panel, allows conversion of the instrument so that it may be operated from one line voltage or the other. In addition, this assembly changes the connections of the power transformer primary to allow selection of one of three regulating ranges (see Table 2-1). The assembly also includes the two line fuses. When the instrument is converted from 115-volt to 230-volt operation or vice versa, the assembly selects the proper fuse to provide the correct protection for the instrument.

The Type 576 may be operated from either a 50 Hz or a 60 Hz line frequency. In order to synchronize the step generator with the collector supply, the 60 Hz-50 Hz switch, located on the Type 576 rear panel below the LINE VOLTAGE SELECTOR assembly, must be set to the position which corresponds to the line frequency being used.

Use the following procedure to convert this instrument between line voltages, regulating ranges or line frequencies:

1. Disconnect the instrument from the power source.

TABLE 2-1

Regulating Ranges

	Regulating Range
Range Selector Switch Position	115 Volts Nominal	230 Volts Nominal 180 to 220 volts
LO (switch bar in left holes)	90 to 110 volts	230 Volts Nominal 180 to 220 volts
M (switch bar in middle holes)	104 to 126 volts	208 to 252 volts
HI (switch bar in right holes)	112 to 136 volts	224 to 272 volts

Fig. 2-1. Line Voltage Selector assembly and 60 Hz switch on the rear panel (shown with cover removed)

Page 20

Fig. 2-2. Front-panel controls, connectors and readout.

(C)

Page 21

3. To convert from 115-volt to 230-volt line voltage or vice versa, pull out the Voltage Selector switch bar (see Fig. 2-1); turn it 180° and plug it back into the remaining holes. Change the line-cord power plug to match the power-source receptacle or use a 115-to-230-volt power plug adapter.

4. To change regulating ranges, pull out the Range Selector switch bar (see Fig. 2-1) slide it to the desired position and plug it back in. Select a range which is centered about the average line voltage to which the instrument is to be connected (see Table 2-1).

5. Re-install the cover and tighten the two captive screws.

6. To convert from operation with 60 Hz line frequency to operation with 50 Hz line frequency (or vice versa), slide the 60 Hz-50 Hz switch (see Fig. 2-1) to the position which coincides with the line frequency being used.

7. Before applying power to the instrument, check that the indicating tabs on the switch bars are protruding through the correct holes in the voltage selector assembly cover for the desired line voltage and regulating range.

CAUTION

The Type 576 should not be operated with the Voltage Selector switch or the Range Selector switch in the wrong position for the line voltage applied. Operation of the instrument with either of these switches in the wrong position will cause incorrect operation and may damage the instrument.

CONTROLS, CONNECTORS AND READOUT

All controls and connectors required for normal operation of the Type 576 are located on the front and rear panels of the instrument and on the front panel of the standard test fixture (see Figs. 2-2 and 2-3). In addition, readout of some of the instrument functions has been provided on the front panel. Familiarity with the function and use of each of these controls, connectors and the readout is necessary for effective operation of the instrument. The functions are described in the following table.

CRT and Readout

Controls

NTENSITY Control

Controls brightness of display.

Provides adjustment for optimum displav definition.

Fig. 2-3. Rear-panel controls.


READOUT ILLUM CONTROL	Controls brightness of readout.
SCALE ILLUM Control	Controls graticule illumination.
Connector
CAMERA POWER Connector	Provides +15 volts for operation of camera.
Readouts
PER VERT DIV Readout	Readout indicates deflection factor of vertical display as viewed on CRT.
PER HORIZ DIV Readout	Readout indicates deflection factor of horizontal display as viewed on CRT
PER STEP Readout	Readout indicates amplitude per step of Step Generator output.
β OR g _m PER DIV Beadout	Readout indicates beta or trans conductance per division of CRT dis

Display Sensitivity and Positioning

VERTICAL CURRENT/DIV	Selects vertical deflection factor of display.
Switch	COLLECTOR—Normal operation of instrument. Vertical display rep- resents collector current. Use black units to determine vertical deflec- tion factor.

Page 22

EMITTER-Operation of instrument with MODE switch set to LEAKAGE (EMITTER CUR-RENT). Vertical display represents emitter current. Use orange units to determine vertical deflection factor. STEP GEN-Steps indicating Step Generator output are displayed vertically. AMPLITUDE switch setting per division determines vertical deflection factor.

DISPLAY OFFSET Allows selection of display offset or Selector Switch display offset and magnification.

NORM (OFF)—Display offset is not operable.

HORIZ X1–Allows horizontal display to be offset using calibrated CENTERLINE VALUE switch.

VERT X1—Allows vertical display to be offset using calibrated CEN-TERLINE VALUE switch.

HORIZ X10-Horizontal display magnified by 10 times. Allows horizontal display to be offset using calibrated CENTERLINE VALUE switch.

VERT X10—Vertical display magnified by 10 times. Allows vertical display to be offset using calibrated CENTERLINE VALUE switch.

CENTERLINE VALUE Switch

(Clear plastic flange with numbers on it) Provides calibrated offset of display.

X1 (VERT or HORIZ)—Number on CENTERLINE VALUE switch appearing in blue window represents number of divisions centerline of display is offset either vertically or horizontally from zero offset line.

X10 (VERT or HORIZ)—Number on CENTERLINE VALUE switch appearing in blue window multiplied by 10 represents number of divisions centerline of display is offset either vertically or horizontally from zero offset line.

HORIZONTAL VOLTS/DIV Switch

of display. COLLECTOR-Horizontal display represents collector voltage to

Selects the horizontal deflection factor

ground. BASE—Horizontal display represents base voltage to ground.

STEP GEN-Steps indicating Step Generator output are displayed horizontally. AMPLITUDE switch setting per division determines hori-

zontal deflection factor.

ZERO Button

CAL Button

Provides a zero reference for the dis-

NORM---When DISPLAY OFFSET selector switch is set to NORM (OFF), ZERO button provides point on CRT of zero vertical and horizontal-deflection for adjusting position controls.

DISPLAY OFFSET—When DIS-PLAY OFFSET Selector switch is in one of four display offset positions, ZERO button provides reference point on CRT which must be positioned to vertical centerline (horizontal offset) or to horizontal centerline (vertical offset) to insure that the CENTERLINE VALUE switch setting applies to centerline. (Should always be checked with DISPLAY OFFSET Selector switch set to MAGNIFIER.)

Provides signal which should cause 10 divisions of vertical and horizontal deflection for checking calibration of vertical and horizontal amplifiers

NORM—When DISP! AY OFFSET selector switch is set to NORM (OFF), CAL button provides point on CRT of 10 divisions of vertical and horizontal deflection.

DISPLAY OFFSET—When DIS-PLAY OFFSET Selector switch is in one of four display offset positions, CAL button provides signal which should cause reference point on CRT to appear on vertical centerline (horizontal offset) or on horizontal centerline (vertical offset), assuming zero reference point was properly adjusted. (Check should be performed with DIS-PLAY OFFSET Selector switch set to MAGNIFIER.)

DISPLAY INVERT	Inverts display vertically and horizon-
Button	tally about center of CRT.
POSITION Switch	Provides coarse positioning of horizon-
(Horizontal)	tal display.
FINE POSITION Control (Horizontal)	Provides fine positioning of horizontal display.
POSITION Switch (Vertical)	Provides fine positioning of vertical display.

Page 23

FINE POSITION Control (Vertical)

Provides fine positioning of vertical display.

Collector Supply

Controls

ΜΑΧ ΡΕΑΚ VOLTS Switch

Selects range of VARIABLE COLLEC-TOR SUPPLY control. Switch is located below PEAK POWER WATTS switch and range is indicated by white arrow. When switch is set to 75, 350 and 1500, protective box must be used with Standard Test Eixtures (see section on interlock system).

WATTS Switch

Selects nominal peak power output of Collector Supply, by selecting resistance in series with Collector Supply output, PEAK POWER WATTS is indicated by number on transparent switch flange appearing above white MAX PEAK VOLTS indicator SERIES RESISTORS are indicated by black indicator. PEAK POWER WATTS switch must be pulled out to set nominal peak nower output. When PEAK POWER WATTS switch is set series resistance is automatically changed to maintain desired nominal peak power output when MAX PEAK VOLTS switch setting is changed

VARIABLE COL- Allows varving of collector supply Control

LECTOR SUPPLY voltage within range set by MAX PEAK VOLTS switch

POLABITY Switch Selects polarity of Collector Supply voltage and Step Generator output.

-(PNP)-Collector Supply voltage and Step Generator output are negative-going +(NPN)-Collector Supply voltage

and Step Generator output are positive-aoina.

AC-Collector Supply voltage is both positive- and negative-going (sine wave); Step Generator output is positive-agina. When switch is set to AC position, use .5X step rate and normal mode of operation

10DE Switch	Selects mode of operation of Collector
	Supply.
	NORM–Normal Collector Supply
	output is obtained.
	DC (ANTILOOP)-Collector Sup-
	ply output is DC voltage equal to
	peak value set by VARIABLE COL-
	LECTOR SUPPLY control.

Operating Instructions-Type 576

LEAKAGE (EMITTER CUR-RENT)-Vertical sensitivity is increased 1000 times. Vertical amplifier measures emitter current. Collector Supply mode set for DC voltage output.

Allows adjustment of looping compen-COMPENSATION sation. Allows compensation of inter-Control nal and adapter stray canacitance Does not compensate for device capacitance.

Resets Collector Supply if it has been SUPPLY RESET disabled by internal circuit breaker. Collector Supply is turned off whenever maximum current rating of transformer primary of 12 Amperes is exceeded

POWER ON-OFF Controls input power to instrument. Switch

Lights when power is on

Liahts

POWER Light

COLLECTOR SUPPLY VOLT-AGE DISABLED Light

Indicates Collector Supply voltage has been disabled Lights when Collector Supply may present a potentially dangerous voltage at its output. In such a case, use of protective box is required to enable Collector Supply. Also lights when high current generated by Collector Supply or Step Generator causes instrument to overheat

Step Generator

Controls

NUM

CHE

EEM

STE

AME

Swit

OFF Butt

ABER OF PS Switch	Selects number of steps per family of Step Generator output.
RENT	Provides current limit of the Step Gen- erator output when voltage steps are being produced.
P/OFFSET PLITUDE ch	Selects amplitude per step of steps and offset of Step Generator output. Amplitudes within black arc represent current steps; within yellow arc, volt- age steps. Note caution on front-panel when using voltage steps.
SET ons	Allows offsetting of Step Generator output using OFFSET MULT control. ZERO–No offset available. AID–Allows zero step of Step Gen- erator output to be offset as many

level.

as 10 steps above its zero offset

Page 24

OPPOSE—Allows zero step of Step Generator output to be offset as many as 10 steps below its zero offset level.

OFFSET MULT Control Provides calibrated offset of step Generator output to ±10 times AMPLI-TUDE setting when either OFFSET AID or OFFSET OPPOSE button is pressed.
STEPS Button Provides steps of normal duration (step lasts for entire period of rate cycle).

PULSED STEPS Allows Step Generator output to be applied to Device Under Test for only a portion of normal step duration. Pulsed steps occur at peak of Collector Supply output. 300 us-Selects pulsed steps with

duration of 300 μs. Collector Supply is automatically switched to DC mode. 80 μs-Selects pulsed steps with

duration of 80 µs. Collector Supply is automatically switched to DC mode. 300 µs and 80 µs–When buttons

are pressed together, selects pulsed steps with duration of 300 µs; however, Collector Supply is not automatically switched to DC mode.

Allows steps to be generated in repeti-

STEP FAMILY Buttons

tive families or one family at a time. ON REP—Provides repetitive Step Generator output. OFF SINGLE—Provides one family of steps whenever button is pressed. Once button has been pressed, Step Generator is turned off until

pressed again or until ON REP button is pressed.

TE Buttons Selects rate at which steps are generated.

NORM—Provides normal Step Generator rate of 1X normal Collector Supply rate (120 steps per second for 60 Hz line frequency). 2X—Provides rate of two times por-

mal rate.

mal rate. 2X and .5X–When buttons are

2X and .5X—when buttons are pressed together, provides normal rate but with step transistions occuring at peak of Collector Supply sweep.

STEP/OFFSET POLARITY IN-VERT Button

Allows change of polarity of Step Generator output (from polarity set by POLARITY switch).

STEP MULT .1X Button

Provides 0.1 times multiplication of step amplitude, but does not effect offset.

Standard Test Fixture

Controls

Terminal Selector Switch

Selects way in which Step Generator is applied to Device Under Test. In all positions Collector Supply output is connected to Collector terminal.
- EMITTER GROUNDED—Emitter of Device Under Test is connected to ground.
  - STEP GEN—Step Generator is applied to base terminal of Device Under Test. Normal operating position.

OPEN (OR EXT)—Base terminal of Device Under Test open. External signal applied to EXT BASE OR EMIT INPUT connector, will be applied to base terminal.

SHORT—Base terminal of Device Under Test is shorted to emitter terminal.

BASE GROUNDED—Base terminal of Device Under Test is connected to ground. Step Generator polarity is inverted.

OPEN (OR EXT)—Emitter terminal of Device Under Test is open. External signal applied to EXT BASE OR EMIT INPUT connector, will be applied to emitter terminal.

STEP GEN—Inverted Step Generator output is applied to emitter of Device Under Test. LEET-OFE-BIGHT Selects which device (choice of 2) is to

witch be tested, left or right.

ck Enables Collector Supply when Protective Box is in place and lid is closed.

Connectors

Adapter	Allows	con	nect	ic
Connectors	adapters	to	Sta	ın
	Connecto	rs	will	2

Allows connection of various test adapters to Standard Test Fixture. Connectors will accept standard size

Page 25

banana plugs if some other means of connecting Device Under Test to Standard Test Fixture is desired. C, B and E stand for collector, base and emitter, respectively. Unlabeled terminals allow Kelvin sensing of voltage for high current devices

STEP GEN OUT Connector

EXT BASE OR EMIT INPUT Connector

GROUND

Light

Caution Light

Step Generator output signal appears at this connector

Allows input of externally generated signal to either base terminal or emitter terminal of Device Under Test as determined by Terminal Selector Switch.

Provides external access to ground reference.

Red light on, indicates Collector Supply is enabled and dangerous voltage may appear at collector terminals.

erating voltage and line voltage range.

Voltage Selector-Selects operating

Bange Selector-Selects line voltage

colocte on

Rear Panel

Switch accomply

Also includes line fuses

voltage (115 V or 230 V)

range (low medium high)

Controls

Line Voltage Selector Switches

60 Hz-50 Hz Switch

Allows conversion of instrument for operation with either 60 Hz

FRONT PANEL COLORS

The various colors on the front-panel of the Type 576 and Standard Test Fixture indicate relationships between controls and control functions. Table 2-2 shows the relationship which each color indicates

Table	2-2

Colors and Controls

Color	Relationship
Green	Indicates controls which affect the Step Generator polarity.
Blue	Indicates controls and statements as sociated with display offset. Indicates relationship of LEAKAGE (EMITTER CURRENT) mode with the VERTICAL and HORIZONTAL switches.
Orange

Yellow	Indicates controls and statements as- sociated with the voltage mode of op- eration of the Step Generator.
Black (Buttons)	Indicates function controlled by a single button, which is released for most common applications.
Dark Grey (Buttons)	Indicates function controlled by sever- al buttons, and the dark grey button is pressed for most common applica- tions.

PRECAUTIONS

A number of the Type 576 front-panel controls could, through improper use, cause damage to the device under test. Fig. 2-4 indicates the area of the Type 576 front panel where these controls are located. Care should be exercised when using controls located in this area.

Fig. 2-4. Controls located in light area of Type 576 front-pane could cause damage to a device under test if used improperly.

GENERAL DESCRIPTION OF INSTRUMENT OPERATION

The Type 576 is a semiconductor tester which displays and allows measurement of both static and dynamic semiconductor characteristics obtained under simulated operating conditions. The Collector Supply and the Step Generator produces voltages and currents which are applied to the device under test. The display amplifiers measure the effects of these applied conditions on the device under test

2-7

Page 26

The result is families of characteristics curves traced on a CRT.

The Collector Supply circuit normally produces a fullwave rectified sine wave which may be either positive- or negative going. The amplitude of the signal can be varied from 0 to 1500 volts as determined by the MAX PEAK VOLTS switch and the VARIABLE COLLECTOR SUPPLY control. This Collector Supply output is applied to the collector (or equivalent) terminal of the device under test

The Step Generator produces ascending steps of current or voltage at a normal rate of one step per cycle of the Collector Supply. The amount of current or voltage per step is controlled by the AMPLITUDE switch and the total number of steps is controlled by the NUMBER OF STEPS switch. This Step Generator output may be applied to either the base or the emitter (or equivalent) terminals of the device under test.

The display amplifiers are connected to the device under test. These amplifiers measure the effects of the Collector Supply and of the Step Generator on the device under test, amplify the measurements and apply the resulting voltages to the deflection plates of the CRT. The sensitivities of these amplifiers are controlled by the VERTICAL CUR-RENT/DIV switch and the HORIZONTAL VOLTS/DIV switch.

Fig. 2-5 is a block diagram showing the connection of these circuits to the device under test for a typical measurement.

FIRST TIME OPERATION

When the Type 576 is received, it is calibrated and should be performing within the specification shown in Section 1. The following procedure allows the operator to become familiar with the front panel controls and their functions as well as how they may be used to display transistor or diode characteristics. This procedure may also be used as a general check of the instrument's performance. For a check of the instrument's operation with respect to the specification given in Section 1, the Performance Check and Calibration Procedure in Section 5 must be used

1. Apply power to the Type 576.

2. Allow the instrument to warm up for a few minutes Instrument should operate within specified tolerances 5 minutes after it has been turned on.

3. Set the Type 576 and Standard Test Fixture frontpanel controls as follows:

READOUT ILLUM	Fully counterclockwise
GRATICULE ILLUM	Fully counterclockwise
INTENSITY	Fully counterclockwise
FOCUS	Centered
VERTICAL	1 mA

Page 27

DISPLAY OFFSET Selector	NORM (OFF)	CRT ar
CENTERLINE VALUE	0	4. Tu
HORIZONTAL	1 V COLLECTOR	the con-
Vertical POSITION	Centered	manna
Vertical FINE POSITION	Centered	5. Tu
Horizontal POSITION	Centered	titles bec
Horizontal FINE POSITION	Centered	set the readout per vert
ZERO	Released	step and
CAL	Released	6. T appears
DISPLAY INVERT	Released	ing the (
MAX PEAK VOLT,S	15	- the sport
PEAK POWER WATTS	0.1	just the
VARIABLE COLLEC- TOR SUPPLY	Fully Counterclockwise	Positio 8. T
POLARITY	AC	out its ±2.5 di
MODE	NORM	trol so t cule.
LOOPING COMPENSATION	As is	9. R control.
NUMBER OF STEPS	1
CURRENT LIMIT	20 mA	10. I that the
AMPLITUDE	.05 µA	switch is
OFFSET	ZERO	this case the POS
STEPS	Pressed	11. 1
PULSED STEPS	Released	TION sv
STEP FAMILY	REP ON	12. S
RATE	NORM	cule.
POLARITY INVERT	Released	13. S
STEP MULT .1X	Released	cule.
Terminal Selector	BASE TERM STEP GEN	Vertica
LEET-OFE-BIGHT	OFF	14 4

CRT and Readout Controls

4. Turn the GRATICULE ILLUM control throughout its range. Note that the graticule lines become illuminated as the control is turned clockwise. Set the control for desired illumination.

5. Turn the READOUT ILLUM control throughout its range. Note that the fiber-optic readouts and the readout titles become illuminated as the control is turned clockwise. Set the control for the desired readout illumination. The readout should read for these initial control settings; 1 mA per vertical division, 1 V per horizontal division, 50 nA per step and 20 k β or g_m per division.

6. Turn the INTENSITY control clockwise until a spot appears at the center of the CRT graticule. To avoid burning the CRT phosphor, adjust the INTENSITY control until the spot is easily visible, but not overly bright.

7. Turn the FOCUS control throughout its range. Adjust the FOCUS control for a sharp, well-defined spot.

Positioning Controls

8. Turn the vertical FINE POSITION control throughout its range. Note that the control has a range of at least ±2.5 divisions about the center horizontal line. Set the control so that the spot is centered vertically on the CRT graticule.

9. Repeat step 8 using the horizontal FINE POSITION control.

10. Turn the vertical coarse POSITION switch. Note that the spot moves 5 divisions vertically each time the switch is moved one position. (The most extreme positions of the switch represent 10 divisions of deflection, which in this case causes the spot to be off the CRT graticule.) Set the POSITION-switch to the center position.

11. Repeat step 10 using the horizontal coarse POSI-TION switch.

12. Set the POLARITY switch to --(PNP). Note that the spot moves to the upper right corner of the CRT graticule.

13. Set the POLARITY switch to +(NPN). Note that the spot moves to the lower left corner of the CRT graticule.

Vertical and Horizontal Sensitivity

14. Install the diode adapter (Tektronix Part No. 013-

Page 28

Fig. 2-6. Display of I vs. V for a 1 kΩ resistor using various settings of the VERTICAL and HORIZONTAL switches.

0111-00) into the right-hand set of accessory connectors located on the Standard Test Fixture.

15. Install a 1 kΩ, 1/2 watt resistor in the diode adapter.

16. Set the LEFT-OFF-RIGHT switch to RIGHT and turn the VARIABLE COLLECTOR SUPPLY control until a trace appears diagonally across the CRT.

17. Turn the VERTICAL switch clockwise and note that as the vertical deflection factor decreases the slope of the line increases (see Fig. 2-6). Turn the VERTICAL switch counterclockwise from the 1 mA position and note that the slope decreases. Also note that the PER VERT DIV readout changes in accordance with the position of the VERTICAL switch. Reset the VERTICAL switch to 1 mA.

18. Repeat step 17 using the HORIZONTAL switch within the COLLECTOR range of the switch. The change in slope of the trace will be the inverse of what it was for the VERTICAL switch. Reset the HORIZONTAL switch to 1 V COLLECTOR.

19. Press the ZERO button. Note that the diagonal trace reduces to a spot in the lower left corner of the CRT graticule. This spot denotes the point of zero deflection of the vertical and horizontal amplifiers. Release the ZERO button.

20. Press the CAL button. Note that the diagonal trace reduces to a spot in the upper right corner of the CRT graticule. The position of this spot indicates 10 divisions of deflection both vertically and horizontally. Release the CAL button,

21. Press the DISPLAY INVERT button and turn the VARIABLE COLLECTOR SUPPLY control counterclockwise. Note that the display has been inverted and is now originating from the upper right corner of the CRT graticule. Release the DISPLAY INVERT button.

Fig. 2-7. Type 576 Standard Test Fixture with protective box in stalled for safe operation.

Collector Supply

22. Turn the MAX PEAK VOLTS switch throughout its range. Note that when the switch is in the 75, 350 and 1500 positions, the yellow light comes on.

23. While the yellow light is on, turn the VARIABLE COLLECTOR SUPPLY control fully clockwise. Note that the diagonal line obtained in step 16 does not appear. When the yellow light is on, the Collector Supply is disabled.

Set the following Type 576 controls:
MAX PEAK VOLTS	75
VARIABLE COLLECTOR SUPPLY	Fully counterclockwise
LEET-OFE-BIGHT	OFF

25. Install the protective box on the Standard Test Fixture as shown in Fig. 2-7.

26. Close the lid of the protective box and note that the yellow light turns off and the red light turns on.

WARNING

The red light indicates that dangerous voltages may appear at the collector terminals of the Standard Test Fixture.

27. Set the LEFT-OFF-RIGHT switch to RIGHT and turn the VARIABLE COLLECTOR SUPPLY control clockwise. Note that the diagonal trace appears indicating that the Collector Supply has been enabled.

2-10

Page 29

28. Set the following Type 576 controls to:

MAX PEAK VOLTS 15

VARIABLE COLLECTOR Fully Counterclockwise SUPPLY

(The protective box may be removed if desired.)

29. Turn the VARIABLE COLLECTOR SUPPLY control until the diagonal trace reaches the center of the CRT graticule. Pull out on the PEAK POWER WATTS switch and set it to 220. Note that the diagonal trace lengthens as the switch is turned through its range. Also note that the SERIES RESISTORS decrease as the maximum peak power is increased.

30. Allow the MAX PEAK VOLTS switch and the PEAK POWER WATTS switch to become interlocked and switch to 75. Note that the maximum peak power value remains at 220 and that the SERIES RESISTORS values change.

31. Set the following Type 576 controls to:

1 1 001 1 50700
.1 V COLLECTOR
15
Fully Counterclockwise

0.1
OFF

32. Remove the resistor from the diode adapter and replace it with a silicon diode. Align the diode so that its cathode is connected to the emitter terminal.

33. Set the LEFT-OFF-RIGHT switch to RIGHT and turn the VARIABLE COLLECTOR SUPPLY control clockwise. Note the display of the forward voltage characteristic of the diode. (see Fig. 2-8).

34. Set the COLLECTOR SUPPLY POLARITY switch to –(PNP). Note the display of the reverse voltage characteristic of the diode (see Fig. 2-8).

Fig. 28. Display of forward and reverse bias characteristics of a signal diode.

35. Set the following Type 576 controls to: POLABITY + (NPN)

MODE DO

Note that the display of the forward voltage diode characteristic has become a spot. The spot indicates the current conducted by the diode and the voltage across it.

36. Turn the VARIABLE COLLECTOR SUPPLY control counterclockwise. Note that the spot traces out the diode characteristic.

37	7. Set the following Type 5 VERTICAL	76 controls to: 1 μΑ
	HORIZONTAL	2 V COLLECTOR
	Vertical POSITION	Display Centered
	VARIABLE COLLEC- TOR SUPPLY	Fully Clockwise
	MODE	NORM
	LEET-OFE-BIGHT	LEET

38. Adjust the LOOPING COMPENSATION control for minimum trace width (see Fig. 2-9).

Fig. 2-9. Adjustment of LOOPING COMPENSATION control

35	Set the following Type 5 VERTICAL	56 controls to: Б mA
	Vertical POSITION	Switch centered
	VARIABLE COLLEC- TOR SUPPLY	Fully Counterclockwise
	POLARITY	AC
	LEFT-OFF-RIGHT	OFF

Page 30

40. Remove the diode from the diode adapter and replace it with an 8 volt Zener diode. Align the diode so that its cathode is connected to the emitter terminal.

41. Set the LEFT-OFF-RIGHT switch to RIGHT and turn the VARIABLE COLLECTOR SUPPLY control clockwise. Note that the display shows both the forward and reverse characteristics of the Zener diode (see Fig. 2-10).

Fig. 2-10. Display of Zener diode 1 vs. V characteristic with PO-LARITY switch set to AC.

Display Offset and Magnifier

42. Set the Type 576 POLARITY switch to –(PNP). Note the display of the reverse voltage characteristic of the Zener diode.

Note the display of the reverse voltage characteristic of the Zener diode.

43. Position the display to the center of the CRT graticule with the vertical POSITION switch (see Fig. 2-11A).

44. Set the DISPLAY OFFSET Selector switch to HORIZ X10. Press the ZERO button and, using the horizontal FINE POSITION control, adjust the spot so that it is on the center vertical line of the CRT graticule. This spot position represents the zero offset position. Release the ZERO button and set the DISPLAY OFFSET Selector switch to HORIZ X1.

45. Turn the CENTERLINE VALUE switch from the 0 position counterclockwise, until the Zener breakdown portion of the display is within ±0.5 divisions of the center vertical line (see Fig. 2-11B). Note the number on the CENTERLINE VALUE switch which appears in the blue window below the word DIV. This number multiplied by the PER HORIZ DIV readout value gives the approximate value of the breakdown voltage of this Zener diode. For the diode in the example shown in Fig. 2-11, the approximate Zener breakdown voltage is 4 divisions times 2 V/division = 8 volts.

46. Set the DISPLAY OFFSET Selector switch to

HORIZ X10. Note that PER HORIZ DIV readout value has changed to indicate the 10 times multiplication. By expanding the scale, a measurement can be made of that part of the characteristic which was not quite offset to the center vertical line of the CRT graticule (see Fig. 2-11C). This value when added to the approximate value (or subratcted

Fig. 2-11. Displays of measurement of Zener breakdown voltage using the DISPLAY OFFSET Selector and CENTERLINE VALUE switches, (A) DISPLAY OFFSET Selector switch set to HORIZ X1 and CENTERLINE VALUE switch set to 0; (B) CENTERLINE VALUE switch set to 4; (C) DISPLAY OFFSET Selector switch set to HORIZ X10.

if the approximate value was greater than the actual value) produces a more exact measurement of the breakdown voltage. In the example shown in Fig. 2-11, 400 mV should be

Page 31

added to the approximate estimate, yielding a value of 8.4 for the Zener voltage of the diode. The same process can also be carried out using vertical display offset and magnification.

Step Generator

7. Set the following Type 576 controls to:
DISPLAY OFFSET Selector	NORM (OFF)
CENTERLINE VALUE HORIZONTAL Vertical POSITION	0 1 V COLLECTOR Switch centered
POLARITY	+(NPN)
VARIABLE COLLEC- TOR SUPPLY	Fully Counterclockwise
LEFT-OFF-RIGHT	OFF

48. Remove the diode adapter and replace it with a transistor adapter (Tektronix Part No. 013-0098-02).

49. Place an NPN silicon transistor into the right tran sistor test socket of the universal transistor adapter.

50. Set the LEFT-OFF-RIGHT switch to RIGHT and turn the VARIABLE COLLECTOR SUPPLY clockwise until the peak collector-emitter voltage is about 10 volts.

51. Turn the AMPLITUDE switch until a step appears on the CRT. Note that the greater the step amplitude, the greater the collector current (see Fig. 2-12). Set the AMPLI-TUDE for the minimum step amplitude which produces a noticeable step in the display.

Fig. 2-12. Collector current vs. Collector-Emitter voltage for various settings of the AMPLITUDE switch.

52. Turn the NUMBER OF STEPS switch clockwise. Be sure the PEAK POWER WATTS switch is set within the power dissipation rating of the transistor being used. Note the display of collector current vs. collector-emitter voltage for ten different values of base current (see Fig. 2-13A).

Fig. 2-13. (A) I_C vs. V_CE for 10 steps of base current at 50 µA per step; (B) I_C vs. V_BE for 10 steps of lease current at 50 µA per step.

53. Set the HORIZONTAL switch to .1 V BASE. Note the display of the collector current vs. base-emitter voltage for ten different values of base current (see Fig. 2-13B).

54. Set the VERTICAL switch to STEP GEN and the HORIZONTAL switch to 1 V COLLECTOR. Note the display of the base current, one step per vertical division, vs. the collector-emitter voltage (see Fig. 2-14A).

55. Set the HORIZONTAL switch to .1 V Base. Note the display of base current, one step per vertical division, vs. base-emitter voltage (see Fig. 2-14B)

56. Set the VERTICAL switch to 5 mA and the HORI-ZONTAL switch to STEP GEN. Note the display of collector current vs. base-current, one step per horizontal division (see Fig. 2-15).

57. Set the following Type 576 controls to:

HORIZONTAL	1 V COLLECTOR
RATE	.5X

Note that the step rate is slower than the normal rate.

Page 32

Fig. 2-15. IC vs. IB, IB @ 50 µA per division.

58. Press the NORM RATE button and then the 2X RATE button. Note that the step rate is faster than the normal rate.

59. Press both the 2X RATE and .5X RATE buttons. Note that the step rate is normal, but that the steps occur

at the peak of each collector sweep, rather than at the beginning of each collector sweep, as when the NORM RATE button is pushed.

60. Press the SINGLE STEP FAMILY button. Press it again. Note that each time the SINGLE button is pressed, a single family of characteristic curves is displayed and then the Step Generator turns off.

61. Set the following Ty	ype 576 controls to:
STEP FAMILY	REP ON
RATE	NORM
PULSED STEPS	300 µs

Note that the collector supply is in the DC mode and that each step is in the form of a pulse. (See Fig. 2-16A.) (Readjustment of the INTENSITY control may be necessary.)

62. Press the 80 µs button. Note that the duration of each pulsed step is reduced.

63. Press both the 300 µs and the 80 µs buttons. Note that the Collector Supply is in the normal mode and the steps are occurring at the peak of the collector sweep, with a duration as observed in step 61 (see Fig. 2-16B).

Page 33

64. Set the Type 576 LEFT-OFF-RIGHT switch to OFF and remove the universal transistor adapter from the Standard Test Fixture. (Leave the transistor in the adapter). Install the universal FET adapter (Tektronix Part No. 013-0099-02) on the Standard Test Fixture and place an N-channel junction FET into the right test socket of the adapter.

65. Set the following Type 576 controls to:



wise

66. Set the LEFT-OFF-RIGHT switch to RIGHT and turn the VARIABLE COLLECTOR SUPPLY control slowly clockwise. Note the display of drain current vs. drain-source voltage with voltage steps of 0.1 V/step

Fig. 2-17. Display of FET common-source characteristic curves: ID vs. VDS for 10 steps of gate voltage at 0.05 volts/step.

applied to the gate (see Fig. 2-17). Since the steps applied to the gate are positive-going, the curves displayed represent enhancement mode operation of the FET. (Press the SINGLE STEP FAMILY button to locate the curve obtained with zero volts on the gate.)

67. Press the POLARITY INVERT button and note the display of the depletion mode of operation of the FET (see Fig. 2-17). (Press SINGLE STEP FAMILY button for zero bias curve.)

68. Set the Type 576 LEFT-OFF-RIGHT switch to OFF. Remove the universal FET test adapter and replace it with the universal transistor test adapter (with the transistor still in it.)

69. Set the following Type 576 controls to:

VERTICAL	5 mA
AMPLITUDE	Current Step
NUMBER OF STEPS	5
POLARITY INVERT	Released

Set the AMPLITUDE switch and the VARIABLE COLLECTOR SUPPLY control for a family of curves similar to Fig. 2-18A.

70. Note the β or g_m per division readout. By measuring the vertical divisions between two curves of the displayed family, the β of the device in that region can be determined. For example, there is approximately 0.9 division between the fourth and fifth steps shown in Fig. 2-18A. The β of the device when operated in this region is, therefore, approximately 0.9 (100) or (90). To make a more accurate measurement of β, the difference in both collector and base current between the fourth and fifth steps should be less.

71. Press the OFFSET AID button and set the OFFSET MULT control to 4. Note that the offset current has been added to the Step Generator output so that the zero step is now at the level of the fourth step displayed.

72. Press the STEP MULT .1X button. Note that the current per step is now 1/10 of the value set by the AMPLI-TUDE switch. Check the PER STEP readout for the new amplitude per step. (See Fig. 2-18B.)

73. Set the DISPLAY OFFSET Selector switch to VERT X1 and turn the CENTERLINE VALUE switch counterclockwise until the first step is within ±0.5 division of the center horizontal line.

74. Set the DISPLAY OFFSET Selector switch to VERT X10. Note that though the β per division is still 100 as it was in step 70, the change in collector and base current (Δ I_C and ΔI_B) is less between the fourth and the fifth step. This allows for a more accurate measurement of β at the level of the fourth step (see Fig. 2-18C). The β of the device at the fourth step now measures at about 0.8 (100) = 80

75. Set the following Type 576 controls to:

VERTICAL	1 mA
DISPLAY OFFSET Selector	NORM (OFF
AMPLITUDE	.1 V
NUMBER OF STEPS	1
OFFSET MULT	0
STEP MULT	Released

76. Turn the OFFSET MULT control until a step just begins to appear on the CRT. Note the multiplier value on the OFFSET MULT control. This number times the AM-PLITUDE switch setting is the base-to-emitter turn on voltage of the transistor.

Page 34

Fig. 2-18. Measurement of β of transistor, (A) Coarse measurement; (B) Offsetting of display and .1X multiplication of step amplitude; (C) 10X magnification of vertical display.

Standard Test Fixture

77. Set the following Type 576 controls to:

AMPLITUDE	1 μΑ
OFFSET	ZERO
NUMBER OF STEPS	10

78. Adjust the AMPLITUDE switch for a display of the characteristic curves with the emitter grounded and the current steps applied to the base (see Fig. 2-19A).

Fig. 2-19. (A) Terminal Selector switch set to BASE TERM STEP GEN (NORM); (B) Terminal Selector switch set to EMITTER TERM STEP GEN.

79. Set the LEFT-OFF-RIGHT switch to OFF and the STEP FAMILY button to OFF. Take a patch cord with banana plugs on each end and connect it between the STEP GEN OUTPUT connector and the EXT BASE OR EMIT INPUT connector.

80.	Set the following	Type 576 controls to:
S	STEP FAMILY	ON

LEFT-OFF-RIGHT	RIGHT
Terminal Selector	BASE TERM OPEN (OR EXT)
te a display similar to that	seen in step 78.
. Set the following Type 5 VERTICAL	76 controls to: 1 nA EMITTER
MODE	LEAKAGE
VARIABLE COLLEC- TOR SUPPLY	Fully Counterclockwis
STEP ΕΔΜΗ Υ	OFF

Remove the patch cord.

Page 35

82. Turn the VARIABLE COLLECTOR SUPPLY control clockwise and note the display of emitter leakage current with the base terminal open.

83. Set the Terminal Selector switch to SHORT and note the display of emitter leakage current with the base terminal shorted to ground.

84. Set the following Type 576 controls to: VERTICAL 5 mA

AMPLITUDE	5 mA
MODE
Terminal Selector	GEN
STEP FAMILY	ON

Turn the VARIABLE COLLECTOR SUPPLY control clockwise and note the display of collector current vs. collector-emitter voltage with current steps applied to the emitter of the transistor (see Fig. 2-19B).

85. Set the following Type 576 controls to: STEP FAMILY OFF

Terminal Selector	EMITTER TERM OPEN
	(OR EXT)

Reconnect the patch cord between the STEP GEN OUT-PUT connector and the EXT BASE OR EMIT INPUT connector.

86. Set the STEP FAMILY button to ON and note a display similar to that seen in step 84.

This completes the first-time operation.

GENERAL OPERATING INFORMATION CRT

The CRT in the Type 576 has a permanently etched internal graticule. The graticule is 10 divisions by 12 divisions, each division being 1 cm. Illumination of the graticule is controlled by the GRATICULE ILLUM control. Protective shields for the CRT and the fiber-optic readout display are fitted to the bezel. The bezel covers the CRT and the fiber-optic readout display. To remove, loosen the securing screw and pull out on the bottom of the bezel.

A blue filter has been provided to improve the contrast of the display when the ambient light is intense. This filter may be installed (or removed) by removing the bezel and sliding the filter from between the CRT protective shield and the bezel frame.

Readout

The readout located to the right of the CRT is made up of the fiber-optic displays and their titles. The fiber-optic displays show numbers and units (5 mA, 2 V, etc.) the

values of which are a function of front-panel control settings. The titles are words printed on the fiber-optic display shield attached to the bezel. These words indicate the characteristics of the CRT display to which each fiber-optic display is related (PER VERT DIV, PER STEP, etc.). Illumination of the titles and the fiber-optic diplays is controlled by the READOUT ILLUM control. It should be noted that as the illumination of the readout is reduced, the fiber-optic display of β or g_m per division turns off before the other fiber-optic displays.

Intensity

The intensity of the display on the CRT is controlled by the INTENSITY control. This control should be adjusted so that the display is easily visible but not overly bright. It will probably require readjustment for different displays. Particular care should be exercised when a spot is being displayed. A high intensity spot may burn the CRT phosphor causing permanent damage to the CRT.

Focus

The focus of the CRT display is controlled by the FO-CUS control. This control should be adjusted for optimum display definition.

Positioning

The position of the display on the CRT graticule, both vertically and horizontally, is controlled by four sets of controls: the vertical and horizontal POSITION controls, the POLARITY switch, the DISPLAY OFFSET controls and the DISPLAY INVERT, ZERO and CAL buttons.

The position controls provide coarse and fine positioning of the display both vertically and horizontally. Each coarse POSITION switch provides 5-division increments of display positioning. Each FINE POSITION control has a continuous range of greater than 5 divisions. The position controls should not be used to position the zero reference off the CRT. The DISPLAY OFFSET controls may be used for this purpose. If the display is magnified either vertically or horizontally using the DISPLAY OFFSET Selector switch, the ranges of the position controls are increased 10 times.

The POLARITY switch positions the zero signal point of a display (located by pressing the ZERO button) to a position convenient for making measurements on an NPN device, a PNP device or when making an AC measurement.

The DISPLAY OFFSET controls provide calibrated offset (or positioning) of the display either vertically or horizontally. These controls may be used either to make a measurement or to position particular portions of a display, which has been magnified, on the CRT graticule. The DIS-PLAY OFFSET Selector switch determines whether the display will be offset vertically or horizontally and the CEN-TERLINE VALUE switch provides the offset. Under unmagnified conditions, 10 divisions of offset are available. When the DISPLAY OFFSET Selector switch is set to one of its MAGNIFIER positions, 100 divisions of offset are available.

Page 36

When making a measurement using the DISPLAY OFF-SET controls, the CRT graticule becomes a window. When the CENTERLINE VALUE switch is set to 0, the vertical centerline (horizontal offset) or the horizontal centerline (vertical offset) of the window is at the zero signal portion of the display. As the CENTERLINE VALUE switch is turned counterclockwise, the window moves either vertically or horizontally along the display. For each position of the CENTERLINE VALUE switch, the number on the switch appearing in the blue window represents the number of divisions the vertical centerline or the horizontal centerline has been offset from the zero offset line. If the display has been magnified, the number in the blue window must be multiplied by 10.

The ZERO button provides a convenient means of positioning the zero reference point on the CRT araticule Under normal operating conditions (DISPLAY OFFSET Selector switch set to NORM) when the ZEBO button is pressed a zero reference spot appears on the CRT araticule. This spot indicates the point on the CRT where zero signal is being measured by the vertical and horizontal display amplifiers. With the button pressed, the positioning controls may be used to position the spot to a point on the CRT graticule which makes measurements convenient. If the DISPLAY OFESET Selector switch is set to VEBT or HORIZ the zero reference point indicates the horizontal or vertical graticule line, respectively, to which the CENTER-LINE VALUE switch setting applies. To assure the accuracy of the CENTERLINE VALUE switch settings, the zero reference spot should be adjusted (using the positioning controls) to the appropriate centerline for the offset being used. For maximum accuracy of measurement, the position of this zero reference point should be adjusted with the DISPLAY OFFSET Selector switch in one of its MAGNI-FIER positions

The CAL button provides a means of checking the calibration of the display amplifiers. Under normal operating conditions (DISPLAY OFESET Selector switch set to NORM) when the CAL button is pressed, a calibration reference spot appears on the CRT. This spot represents a signal applied to both the vertical and the horizontal display amplifiers which should cause 10 divisions deflection on the CRT graticule both vertically and horizontally. If the position of this spot is compared with the position of the spot obtained when the ZEBO button is pressed the accuracy of calibration of the display amplifiers can be determined. When the DISPLAY OFFSET Selector switch is set to either VERT or HORIZ, the calibration reference spot should appear on the vertical centerline (horizontal offset) or the horizontal centerline (vertical offset), assuming the zero reference point is properly adjusted. This calibration check should be made with the DISPLAY OFF-SET Selector switch in either HOBIZ X10 or VEBT X10 Any departure of the calibration reference spot from the centerline, when this check is made, represents an error of 1% per division in the display offset.

The DISPLAY INVERT button provides a means of inverting the display on the CRT. When the DISPLAY IN-VERT button is pushed, the inputs to the display amplifiers are reversed, causing the display on the CRT to be inverted both vertically and horizontally about the center of the graticule.

If the position controls are centered, the zero and calibration references spots should appear in particular positions on the graticule depending on the positions of the POLARITY switch and the DISPLAY OFFSET Selector switch. Fig. 2-20 shows these positions of the spot for the various settings of the two switches. To determine the spot positions when the INVERT button is pressed, assume the graticule shown is inverted both vertically and horizontally.

Vertical Measurement and Deflection Factor

In the vertical dimension, the display on the CRT measures either collector current (I_C), emitter current (I_E) or the output of the Step Generator. The MODE switch and the VERTICAL switch determine which of these measurements are made.

The Vertical deflection factor of the display on the CRT is controlled by the VERTICAL switch, the DISPLAY OFFSET Selector switch and the MODE switch. The PER VERT DIV readout to the right of the CRT indicates the vertical deflection factor due to the combined effects of these three controls.

Under normal operating conditions, with the MODE switch set to NORM and the DISPLAY OFFSET Selector switch set to NORM (OFF), collector current is measured vertically and the VERTICAL switch determines the vertical sensitivity of the display.

When measuring collector current, the VERTICAL switch provides deflection factors (unmagnified) ranging from 1 µA/division to 2 A/division. The vertical deflection factor is indicated either by the PER VERT DIV readout or by the position of the VERTICAL switch, using the letters printed in black to determine units. The readout and the switch position should coincide.

When the MODE switch is set to LEAKAGE (EMITTER CURRENT) the CRT display measures emitter current vertically. In this case the vertical sensitivity of the display is increased by 1000 times for each position of the VER-TICAL switch. The vertical deflection factor is indicated either by the PER VERT DIV readout or by the position of the VERTICAL switch, using the letters printed in orange to determine units. When the MODE switch is set to LEAK-AGE the output of the Collector Supply is DC voltage, like that obtained when the MODE switch is set to DC (ANTI LOOP), rather than a voltage sweep. Also in the leakage mode a slight error (up to 1.25 V) is added to the horizontal display. The following Horizontal Measurement and Deflection Factor section shows how to determine the degree of this error.

Page 37

Fig. 2-20. Positions of spot on CRT graticule when ZERO or CAL buttons are pressed, for various positions of the POLARITY switch and the DISPLAY OFFSET Selection switch, assuming the position controls are centered.

In the leakage mode of operation, the current sensing resistor is between the emitter and ground. Assuming a constant collector supply output voltage, therefore, emitter current will change whenever the current sensing resistor is changed. The current sensing resistor is changed every decade on the VERTICAL switch. The resulting change in emitter is most evident when the VERTICAL switch is switched between its 5 nA and 10 nA positions or its 50 nA and 100 nA positions.

When the VERTICAL switch is set to STEP GEN, steps indicating the Step Generator output are displayed vertically. The vertical display shows one step per division and the amplitude of each step, as shown by the PER STEP readout, determines the vertical deflection factor. It should be noted that if the HORIZONTAL switch is set to STEP GEN, the Step Generator output signal is not available for display vertically. In this case, setting the VERTICAL switch to STEP GEN causes zero vertical signal to be displayed.

The vertical sensitivity can be increased by 10 times for any of the previously mentioned measurements by setting the DISPLAY OFFSET Selector switch to VERT X10. The magnified vertical deflection factor can be determined either from the PER VERT DIV readout¹ or by dividing the setting of the VERTICAL switch by 10.

¹The PER VERT DIV readout does not indicate deflection factors less than I nA/division.

Horizontal Measurement and Deflection Factor

In the horizontal dimension, the display on the CRT measures either collector to emitter voltage (V_CE), collector to base voltage (V_CB), base to emitter voltage (V_BE), emitter to base voltage (V_EB) or the Step Generator output. The HORIZONTAL switch, the Terminal Selector switch and the parameter being measured vertically determine what is measured horizontally.

The horizontal deflection factor of the display on the CRT is controlled by the HORIZONTAL switch and the DISPLAY OFFSET Selector switch. The PER HORIZ DIV readout to the right of the CRT indicates the horizontal deflection factor due to the combined effects of these two controls.

Under normal operating conditions with collector current being measured vertically, the Terminal Selector switch set to EMITTER GROUNDED and the DISPLAY OFFSET Selector switch set to NORM (OFF), the display will measure V_CE or V_BE horizontally. To measure V_CE, the HORI-ZONTAL switch must be set within the COLLECTOR range which has deflection factors between 50 mV/division and 200 V/division. To measure V_BE, the HORIZONTAL switch must be set within BASE range which has deflection factors between 50 mV/division and 2 V/division. In both cases, the horizontal deflection factors are indicated by both the PER HORIZ DIV readout and the position of the HORIZONTAL switch. The two values should coincide.

Page 38

When the Terminal Selector switch is set to BASE GROUNDED the horizontal display measures collector to base voltage (V_CB) with the HORIZONTAL switch in the COLLECTOR range, or emitter to base voltage (V_EB) with the HORIZONTAL switch in the BASE range. It should be noted that V_EB in this case does not indicate a measurement of the emitter-base voltage under a reverse biased condition. It is a measurement of the forward biased base-emitter voltage with the horizontal sensing leads reversed.

When emitter current is being measured by the vertical display, the only significant measurements made by the horizontal display are V_CE and V_CB. To make these measurements, the HORIZONTAL switch is set within the COLLECTOR range and the Terminal Selector switch is set to EMITTER GROUNDED or BASE GROUNDED.

With the VERTICAL switch set between 500 nA/ division and 1 nA/division, an error occurs in the horizontal measurement. Table 2-3 indicates the degree of this error in voltage per division of vertical deflection for all the settings of the VERTICAL switch within this given range. Using this table and the following procedure, the actual V_CE or V_CB can be caluclated.

TABLE 2-3

Error in Horizontal Voltage Measurement Per Division of Vertical Deflection

VERTICAL Switch Setting ¹	Voltage Error Per Vertical Division
500 nA, 50 nA, 5 nA	125 mV
200 nA, 20 nA, 2 nA	50 mV
100 nA, 10 nA, 1 nA	25 mV

¹EMITTER current, DISPLAY OFFSET Selector switch set to NORM (OFF).

Fig. 2-21. Sample calculation of error in collector to emitter voltage incurred when measuring leakage of a transistor.

1. Measure the vertical deflection of the display in divisions (see Fig. 2-21).

2. Measure the horizontal deflection of the display in volts.

3. Using Table 2-3, find the error factor for the setting of the VERTICAL switch and multiply it by the value determined in step 1.

4. Subtract the voltage determined in step 3 from the voltage determined in step 2 to give the actual V_CE or V_CB.

When the HORIZONTAL switch is set to STEP GEN, steps indicating the Step Generator output are displayed horizontally. The horizontal display shows one step per division and the amplitude of each step, as shown by the PER STEP readout determines the horizontal deflection factor.

The horizontal deflection factor can be increased by 10 times for any of the previously mentioned measurements by setting the DISPLAY OFFSET Selector switch to HORIZ X10². The magnified horizontal deflection can be determined either from the PER HORIZ DIV readout or by dividing the setting of the HORIZONTAL switch by 10.

Measurements

Table 2-4 shows the measurements which are being made vertically and horizontally by the display for the various positions of the VERTICAL switch, the HORIZONTAL switch and the Terminal Selector switch. Those switch position combinations not covered by the table are not considered useful.

Display Offset and Magnifier

The DISPLAY OFFSET Selector switch and the CENTERLINE VALUE switch provides a calibrated display offset of from 0 to 10 divisions (0 to 100 divisions when the display is magnified) and a 10 times display magnifier. The display offset and the display magnifier, when in operation, effect the display either vertically or horizontally, but never the whole display. Use of the calibrate display offset is discussed in the Positioning section. Use of the magnifier is discussed in both the Vertical' and Horizontal Measurement and Deflection Factor sections.

Collector Supply

The Collector Supply provides operating voltage for the device under test. It is a variable voltage in the form of either a sine wave, or a full-wave rectified sine wave (see Fig. 2-22). This voltage is applied to the collector terminals of the Standard Test Fixture.

The MAX PEAK VOLTS switch and the VARIABLE COLLECTOR SUPPLY control determine the peak voltage output of the Collector Supply, which may be varied from 0 volts to 1500 volts. The MAX PEAK VOLTS switch provides four peak voltage ranges: 15 volts, 75 volts, 350 volts and 1500 volts. The VARIABLE COLLECTOR SUPPLY

²The Horizontal display is not calibrated when the VERTICAL switch is set between 500 nA and 1 nA EMITTER.

Page 39


	Switch Settings		Measured	l by Display
VERTICAL	HORIZONTAL	Terminal Selector	Vertically	Horizontally
COLLECTOR	COLLECTOR	EMITTER GROUNDED	IC	VCE
COLLECTOR	BASE	EMITTER GROUNDED	۱ _C	V _BE
COLLECTOR	STEP GEN	EMITTER GROUNDED	IC	IB or VBE
COLLECTOR	COLLECTOR	BASE GROUNDED	IC	VCB
COLLECTOR	BASE	BASE GROUNDED	۱C	VEB ²
COLLECTOR	STEP GEN	BASE GROUNDED	۱C	IB or VEB ²
EMITTER	COLLECTOR	EMITTER GROUNDED	١E	VCE ¹
EMITTER	COLLECTOR	BASE GROUNDED	۱ _B	VCBI
STEP GEN	COLLECTOR	EMITTER GROUNDED	IB or VBE	VCE
STEP GEN	BASE	EMITTER GROUNDED	lB or VBE	V _BE
STEP GEN	COLLECTOR	BASE GROUNDED	IB OF VBE	V _CB
STEP GEN	BASE	BASE GROUNDED	IB or VEB ²	VEB ²

TABLE 2-4

ade by the Type 576 Display

¹Error in voltage must be calculated. See Horizontal Measurements in Deflection Factor section. ²V_ED indicates a measurement of forward voltage base-emitter, with the horizontal voltage sensing leads reversed.

Fig. 2.22 Output of Collector Supply for three settings of PO-I ARITY switch

allows continuous voltage variation of the peak voltage within each neak voltage range.

The PEAK POWER WATTS switch which interlocks with the MAX PEAK VOLTS switch determines the maximum nower output of the Collector Supply Power output is controlled by placing a resistor, selected from the SERIES RESISTORS, in series with the Collector Supply output. The series resistance limits the amount of current which can be conducted by the Collector Supply. In setting

the peak power output using the PEAK POWER WATTS switch the proper series resistor is automatically selected If the peak voltage range is changed while the MAX PEAK VOLTS and the PEAK POWER WATTS switches are interlocked, a new series resistor is chosen which will provide the same peak power output

The Collector Supply POLARITY switch determines the polarity of the Collector Supply output and the Step Generator output. It also provides an initial display position on the CBT graticule as discussed in the section on nosi tioning. When the POLARITY switch is set to +(NPN) the Collector Supply output is a positive-going full wave recti fied sine wave and the Step Generator output is positive aoina. When the switch is set to -(PNP) the Collector Supply output is a negative-going full wave rectified sine wave and the Step Generator output is also negative-going. The AC position of the POLARITY switch provides a Collector Supply output which is an unrectified sine wave, and the Step Generator output is positive-going. A negative-going Step Generator output can be obtained in this case by pressing the STEP/OFFSET POLARITY INVERT button As noted on the front panel, when the AC position is being used, the MODE switch should be set to NORM and the Step Generator rate to 5X

Page 40

The MODE switch determines whether the Collector Supply output voltage will be a voltage sweep or a DC voltage. When the MODE switch is set to NORM the output is a repetitive voltage sweep varying from 0 volts to the peak voltage set by the MAX PEAK VOLTS switch and the VARIABLE COLLECTOR SUPPLY control. When the MODE switch is set to DC (ANTILOOP) or LEAKAGE (EMITTER CURRENT) the Collector Supply output is a DC voltage equal to the peak voltage set by the MAX PEAK VOLTS switch and the VARIABLE COLLECTOR SUPPLY control. This DC voltage may be either positive or negative. The DC mode is very useful when the normal display is exhibiting excessive looping.

Occasionally some of the characteristic curves displayed on the CBT consist of loops rather than well defined lines (see Fig. 2-23). This effect is known as looping and is most noticeable at very low or very high values or current. Looping is generally caused by stray capacitance within the Type 576, and device capacitance. It may also be caused by heating of the device under test. The LOOPING COMPEN-SATION control provides complete compensation for non heat-related looping due to the Type 576 and any standard device adapter which may be used. In general it does not compensate for any added capacitance introduced by the device under test. (Control has some effect in reducing stray capacitance in small diodes and voltage-driven three terminal devices). If uncompensated looping is hindering measurements, the MODE switch should be set to DC (ANTILOOP). If the collector sweep mode of operation (MODE switch set to NORM) is desired, an imaginary line lying inside the loop and equidistant from each side of the loop is the best approximation of the actual characteristic curve (see Fig. 2-23). Looping due to heating may be reduced by using the pulsed steps operation of the Type 576.

Fig. 2-23. Example of a display exhibiting looping.

Interlock System

2.22

Whenever the MAX PEAK VOLTS switch is in the 75, 350 or 1500 positions, the yellow COLLECTOR SUPPLY VOLTAGE DISABLED light comes on. This light indicates that the Collector Supply is disabled. In order to enable the

Collector Supply under these circumstances, the Type 576 uses an interlock system. When the yellow light is on, the protective box must be installed over the accessories connectors (see Fig. 2-7). When the protective box is in place and the lid closed, the yellow light turns off and the red light turns on. The red light indicates that the Collector Supply is enabled and that a dangerous voltage may appear at the Collector terminals. For further information about the interlock system, see the Circuit Description.

Step Generator

The Step Generator provides current or voltage which may be applied to the base or the emitter of the device under test. The output of the Step Generator is families of ascending steps of current or voltage (see Fig. 2-24). When these steps together with the Collector Supply output are applied to the device under test, families of characteristic curves of the device are displayed on the CRT.

The NUMBER OF STEPS switch determines the number of steps per family and has a range of from 1 step to 10 steps. The AMPLITUDE switch determines the amplitude of each step and provides both current steps and voltage steps. The range of step amplitudes available are from 50 nA/step to 200 mA/step for current steps and from 5 mV/step to 2 V/step for voltage steps. The STEP MULT .1X button, when pressed, divides the step amplitude by 10. When voltage steps are being applied to the base of a transistor, the base current increases very rapidly with increasing base voltage (note Caution on front-panel). To avoid damage to the transistor when using voltage steps, current limiting is provided through the CURRENT LIMIT switch.

The rate of generation of steps by the Step Generator is determined by the RATE buttons. When the NORM RATE button is pressed, steps are generated at a rate of 120 steps/second (assuming a 60 Hz line frequency), or one step per cycle of the Collector Supply, POLARITY switch set to +(NPN) or -(PNP). In this case each step occurs at the beginning of a Collector Supply cycle. When the .5X RATE button is pressed, the Step Generator rate is 60 steps/

Page 41

second, or one step per 2 cycles of the Collector supply. Again, each step occurs at the beginning of a Collector Supply cycle. (This rate should be used when the PO-LARITY switch is set to AC.) Pressing the 2X RATE button produces a Step Generator rate of 240 steps/second, 2 steps per cycle of the Collector Supply. In this case steps occur at both the beginning and the peak of a Collector Supply cycle. If the 2X RATE and .5X RATE buttons are pressed together, the Step Generator rate is the normal rate of 120 steps/second except that the steps occur at the peak of each Collector Supply cycle rather than at the beginning as in normal rate operation.

The STEP FAMILY buttons determine whether step families are generated repetitively or one family at a time. Pressing the REP STEP FAMILY button turns the Step Generator on and provides repetitive families of steps. When the SINGLE STEP FAMILY button is pushed, one step family is generated and the Step Generator turns off. To get another step family, the SINGLE button must be pressed again.

The OFESET buttons and the OFESET MULT control allow current or voltage to be either added or subtracted from the Step Generator output. This causes the level at which the steps begin to be shifted either in the direction of the ascending steps (aiding) offset, or in the opposite direction of the steps (opposing) offset When the ZEBO OFESET button is pushed the step family is generated at its nomal level where the zero step level is either 0 mA or 0 V and the OFFSET MULT control is inhibited. When the AID OFFSET button is pressed, current or voltage may be added to the Step Generator output using the OFFSET MULT control. The amount of current or voltage added to the Step Generator output when the AID button is pressed is equal to the setting of the OFFSET MULT control times the setting of the AMPLITUDE switch The OFESET MULT control has a continuous range of 0 to 10 times the setting of the AMPLITUDE switch Pressing the OPPOSE OFESET button allows either current or voltage to be subtracted from the Step Generator output, the amount subtracted determined by the OEESET MULT control. Table 2.5 shows the polarity of the offset current or voltage for the two polarities of the Step Generator output.

Opposing offset is most useful when generating voltage steps to test field effect transistors. When current steps are being generated, the maximum opposing voltage is limited to approximately 2 volts. This voltage limiting protects the base-emitter junction of a bi-polar transistor from reverse breakdown.

The STEP/OFFSET POLARITY INVERT button allows the Step Generator output (both steps and offset) to be inverted from the polarity at which it was set by the POLA-RITY switch. It has no effect when the Terminal Selector switch is set to BASE GROUNDED. Caution should be exercised when using this button to cause reverse current to flow between the base and emitter terminals. Voltage limit-

TABLE 2-5

Polarity of Offset for Polarity of Step Generator Output

Step	OFFSET	Offs	set
Polarity	Buttons	Current	Voltage
Positive going	AID	Positive	Positive
Positive going	OPPOSE	Negative	Negative
Negative going	AID	Negative	Negative
Negative going	OPPOSE	Positive	Positive

ing occurs, when current steps are being generated, only when the OPPOSE OFFSET button is pressed.

When one of the PULSED STEPS buttons is pressed, steps are generated in pulses having durations of either 300 us or 80 us (offset is unaffected). Pulsed operation is useful when testing a device at power levels which might damage the device if applied for a sustained length of time Pulsed steps of a 300 us duration occur when the 300 us PULSED STEPS button is pressed. When the 80 µs PULSED STEPS button is pressed, the duration of the pulsed steps is 80 us. When either the 300 us button or the 80 µs button is pressed, the Collector Supply mode is automatically set to DC. If the 300 µs and 80 µs buttons are pressed together, the Collector Supply remains in the normal mode and 300 µs pulsed steps are produced. In all the previously mentioned cases, the pulses occur at the peak of the Collector Supply sweep and therefore only the normal and .5 times normal Step Generator rates are available for use

Standard Test Fixture

The Standard Test Fixture, which slides into the front of the Type 576, provides a means of connecting the Collector Supply output, the Step Generator output and the display amplifiers to the device to be tested.

The Terminal Selector switch, located on the Standard Test Fixture, determines the state of the base and the emitter terminals of the device under test. The switch has two ranges: EMITTER GROUNDED and BASE GROUNDED. In the EMITTER GROUNDED range, the emitter terminal is connected to ground and the Terminal Selector switch determines the state of the base terminal. With the switch set to STEP GEN, the Step Generator output is applied to the base terminal. In the OPEN (OR EXT) position, the base terminal is left open. In this case measurements may be made with the base terminal left open or with an externally generated signal applied to it through the EXT BASE

Page 42

Page 43

OR EMIT INPUT connector. When the Terminal Selector switch is set to BASE TERM SHORT, the base terminal is shorted to the emitter.

In the BASE GROUNDED range, the base terminal is connected to ground and the Terminal Selector switch determines the state of the emitter terminal. With the switch set to STEP GEN, the Step Generator output is inverted and applied to the emitter terminal. When the switch is set to OPEN (OR EXT) the emitter terminal is left open. In this case, measurements may be made with the emitter terminal left open or with an externally generated signal applied to it through the EXT BASE OB EMIT INPUT connector

Devices to be tested are connected to the Type 576 through 10 accessories connectors provided on the Standard Test Fixture. These connectors allow two devices to be set up at a time for comparison testing. The LEFT-OFF-RIGHT switch determines which device is under test. Tektronix Type 576 test fixture adapters may be plugged into the 10 accessories connectors. These adapters provide sockets into which devices with various lead arrangements may be placed for testing. Table 2-7 lists the test fixture adapters available and their uses. The 10 accessories connectors also accept standard banana plugs so that a device may be connected to the Type 576 without using a specific device testing accessory.

The unlabeled accessories connectors allow Kelvin sensing of voltages measured under high current conditions. Kelvin sensing means that current is supplied to a device under test through one set of contacts and the voltage is measured through another set of contacts. This method of sensing voltage eliminates errors in voltage measurements due to contact resistance. The upper unlabeled accessories connectors on the Standard Test Fixture are used for sensing collector voltage and the lower connectors are for sensing emitter voltage

-----

Conduction of high current through a voltage sensing connector will damage the instrument. When using Kelvin sensing without a special test fixture adapter, separate leads are required for current carrying and for voltage sensing

The STEP GEN OUTPUT connector allows the Step Generator output to be used externally. The EXT BASE OR EMIT INPUT connector allows application of an externally generated signal to either the base or the emitter of the device under test by selection with the Terminal Selector switch. The GROUND connector provides a Type 576 ground reference for signals generated or externally applied to the Type 576

Polarities of the Collector Supply and Step Generator Output

Table 2-8 shows the polarities of the Collector Supply and the Step Gnerator output for various settings of the Collector Supply POLARITY switch and the Terminal Selector switch.

TABLE 2-7

Test Fixture Adapters¹

Tektronix Part Number	Devices Tested	Case Types	se i. Li dise

013-0072-00*	Diodes	Axial lead
013-0098-02	Transistors and P-Channel FET's	TO-18, TO-5 and related sizes	Arac
013-0099-02	N-Channel FET's	TO-18, TO-5 and related sizes	A 100
013-0100-01	Transistors and SCR's	TO-3; provides Kelvin sensing	2410
013-0101-00	Transistors and SCR's	TO-66; provides Kelvin sensing	7
013-0102-00 ²	Transistors and P-Channel FET's	long lead devices = A (⊃o &
013-0103-00 ²	N-Channel FET's	long lead devices
013-0110-00	Diodes	Stud leads; DO-4/DO-5; Kelvin sensing	V
013-0111-00	Diodes	Axial leads; Kelvin sensing	Arso
013-0112-00 ²	Transistors and SCR's	TO-36; Kelvin sensing
013-0124-03 ²	Integrated circuits	multipin device packages; sockets available for 8, 10, 14, 16 pins
013-0127-01 ²	Transistors	Can be rewired for different configurations
013-0138-01	In-line transis- tors and volt- age regulators	B-C-E configuration; can be rewired for other configurations; Kelvin sensing
013-0163-00 ²	Power Tran- sistors	Kelvin sensing

¹Some of these accessories are made of plastic and are susceptible to damage from excessive heat. If a device is likely to heat excessively, a heat sink for the device or the pulsed steps mode of operation should be used.

²Optional accessory

the stand of the stand of the stand

Page 44

TABLE 2-8 Polarities of the Collector Supply and Step Generator Output

Switches			Polarities
Collector Supply POLARITY	Terminal Selector	Collector Supply	Step Generator
(PNP)	EMITTER GROUNDED	Negative going	Negative going ¹
-(PNP)	BASE GROUNDED	Negative going	Positive going
+(NPN)	EMITTER GROUNDED	Positive going	Positive going ¹
+(NPN)	BASE GROUNDED	Positive going	Negative going
AC	EMITTER GROUNDED	Positive and Negative going	Positive going ¹
AC	BASE GROUNDED	Positive and Negative going	Negative going

¹May be inverted by pressing the POLARITY INVERT button.

Page 45

APPLICATIONS

This part of the Operating Instructions describes the use of the Type 576 to measure some basic parameters of bipolar transistors, field effect transistors, unijunction transistors, silicon controlled rectifiers, signal and rectifier diodes, Zener diodes, and tunnel and back diodes. For each of the devices discussed, this section includes tables of Type 576 control settings required to make an accurate measurement without damaging the device under test. Below each table is a block diagram showing the connections of the collector supply, the step generator and the display amplifiers to the device under test, and a picture of a typical characteristic for the semiconductor type being discussed. Also included is a list of common measurements which may be made on

the given devices with the Type 576 and a brief set of instructions on how to make each of these measurements.

This section has been written with the assumption that the reader is familiar with the operation of the Type 576 as described at the beginning of the Operating Instructions. It is also assumed that the reader is familiar with the parameters being discussed.

Control	Required Setting
HORIZONTAL	COLLECTOR
POLARITY	+(NPN) or -(PNP) depending on the transistor type
PEAK POWER WATTS	Less than maximum power rating of device
AMPLITUDE	Current steps
STEPS	Pressed when using low base current
PULSED STEPS	Pressed when using high base current
Terminal Selector	EMITTER GROUNDED BASE TERM STEP GEN for common-emitter family
	BASE GROUNDED EMITTER TERM STEP GEN for common-base family
OFFSET	AID pressed if more than 10 steps are desired

BIPOLAR TRANSISTORS Required Type 576 Control Settings

Common-Emitter Family

Page 46

Some Common Measurements
β (Static)	The static forward current transfer ratio (emitter grounded), hFE, is IC/ ¹ B.
β (Small Signal)	The small-signal short-circuit forward current transfer ratio (emitter grounded), h _fe , is \[\Delta I_C/\Delta I_B. To determine h _fe at various points in a family of curves, multiply the vertical separation of two adjacent curves by the \(\beta \text{ OR g}_m PER DIV readout. To make a more accurate measurement, see steps 69 through 74 of the First Time Operation instructions.
VCE (Sat)	Saturation current and voltage is measured by expanding the display of the saturation region of the device by decreasing the horizontal deflection factor with the HORIZON-TAL switch or the DISPLAY OFFSET MAGNIFIER. Saturation current can be adjusted to the desired operating point with the AMPLITUDE switch.
1 _C vs. V _BE	Base-emitter voltage can be measured by setting the HORIZONTAL switch to the BASE range.
ICEO and BVCEO	Collector-emitter leakage current and collector-emitter breakdown voltage (base open) are measured by setting the Terminal Selector switch to BASE TERM OPEN (OR EXT). For small leakage currents set the MODE switch to LEAKAGE (EMITTER CURRENT). To measure breakdown voltage, increase both the horizontal deflection factor and the collector supply voltage.
ICES and BVCES	Collector-emitter leakage current and collector-emitter breakdown voltage (base shorted to emitter) are measured the same as ICEO and BVCEO except that the Terminal Selector switch is set to BASE TERM SHORT.
ICER and BVCER	Collector-emitter leakage current and collector-emitter breakdown voltage (with a speci- fied resistance between the base terminal and the emitter terminal) are measured the same as ICEO and BVCEO except that a specified resistance is connected between the base terminal and the emitter terminal.

Common-Base Family

Some Common Measurements

The small-signal short-circuit forward current transfer ratio (base grounded), h_fb, can be measured from the common-base family display but is determined most easily by calculating it from the equation C = \mathcal{B}/1 + \mathcal{B}.

Page 47

ICBO and BVCBO

Collector-base leakage current and collector-base breakdown voltage (emitter open) is measured the same as I_CEO and BV_CEO except that the Terminal Selector switch is set to EMITTER TERM OPEN (OR EXT).

IEBO and BVEBO

Emitter-base leakage current and emitter-base breakdown voltage (collector open) is measured the same as I_CBO and BV_CBO except that the device terminals are inverted in the device testing socket (collector lead in the emitter terminal of the socket and the emitter lead in the collector terminal).

FIELD EFFECT TRANSISTORS

Required Type 576 Control Settings

Control	Require	d Setting
HORIZONTAL POLARITY	COLLECTOR +(NPN) for N-chann	el device; –(PNP) for
	P-channel device
PEAK POWER WATTS	Less than maximum	power rating of device
AMPLITUDE	Voltage Steps
STEPS	Pressed
Terminal Selector	EMITTER GROUND GEN	ED BASE TERM STEP
	Enhancement	Depletion
POLARITY INVERT	Released	Pressed
OFFSET with POLARITY INVERT button pressed	OPPOSE	ZERO or AID

Common-Source Family

Some Common Measurements

g_m (Static)

The static transconductance (source grounded) is ID/VGS.

g_m (Small Signal)

The small-signal transconductance (source grounded) is Δ ID/ Δ VGS. To determine g_m at various points in a family of curves, multiply the vertical separation of two adjacent curves by the β OR g_m PER DIV readout. To make a more accurate measurement, see steps 69 through 74 of the First Time Operation instructions.

Page 48

DSS

Drain-source current with zero V _GS is measured from the common-source family, with the Terminal Selector switch set to BASE TERM SHORT. It should be measured above the knee of the curve.

Pinch-Off Voltage (V _p )

Pinch-off voltage (V _p ) can be measured by increasing the depletion voltage with the OFFSET MULT control and the AMPLITUDE switch until the specified pinch-off current is reached by the zero step (zero step only is obtained by pressing SINGLE button). Thus the pinch-off voltage is the setting of the OFFSET MULT control times the setting of the AMPLITUDE switch, to which, for greatest accuracy in the LEAKAGE mode, must be added the error voltage developed between ground and source as per Table 2-3.

BVGSS

Gate-source breakdown voltage with the drain shorted to the source can be measured by putting the gate lead of the device in the drain terminal of the test socket, the source lead in the gate terminal and the drain lead in the source terminal. Set the Terminal Selector switch to BASE TERM SHORT and reverse the collector supply polarity. This measurement should not be made on an insulated-gate device.

UNIJUNCTION TRANSISTORS

Required Type 576 Control Settings

Control	Required Setting
HORIZONTAL	COLLECTOR
POLARITY	+(NPN)
PEAK POWER WATTS	Less than maximum power rating of device
AMPLITUDE	Voltage
OFFSET	AID
STEP FAMILY	OFF (SINGLE)
Terminal Selector	BASE TERM STEP GEN

Some Common Measurements

The intrinsic standoff ratio is VP -VEB₁/VB₂VB₁. In measuring \U03A , VB₂B₁ is determined by the OFFSET MULT control and the AMPLITUDE switch. VB₂B₁ may be measured by setting the HORIZONTAL switch to the BASE range. VP is determined by applying voltage between the emitter and the base₁ terminals using the VARIABLE COLLECTOR SUPPLY control. VP is the voltage at which the emitter-base₁ junction becomes forward biased. VEB₁, the turn on voltage of the emitter-base₁ junction is determined by setting the Terminal Selector switch to BASE TERM OPEN.

Page 49

RB2B1

The interbase resistance can be measured by placing the base₂ lead in the collector terminal of the test socket and the base₁ lead in the emitter terminal. Leave the emitter lead at the device open and apply voltage across the two bases with the VARIABLE COLLECTOR SUPPLY control.

SILICON CONTROLLED RECTIFIERS (SCRs) Required Type 576 Control Settings

Control	Required Setting
HORIZONTAL	COLLECTOR
PEAK POWER WATTS	Less than maximum power rating of device
POLARITY	+(NPN)
STEPS	Pressed when using low gate voltage or current
PULSED STEPS	Pressed when using high gate voltage or current
Terminal Selector	EMITTER GROUNDED BASE TERM STEP GEN

Some Common Measurements

Turn-on

The gate voltage or current at which the device turns on can be measured by applying a specified voltage between the anode and cathode terminals using the VARIABLE COL-LECTOR SUPPLY control and applying current or voltage steps in small increments to the gate with the AMPLITUDE switch.

To measure the forward blocking voltage, set the Terminal Selector switch to BASE TERM OPEN (or SHORT depending on the specification) and turn the VARIABLE COLLECTOR SUPPLY control clockwise until the device switches to its low impedance

Forward Blocking Voltage

Holding Current

Holding current is measured in the same manner as forward blocking voltage. Holding current is the minimum current conducted by the device, while operating in its low impedance state, without turning off.

state. The voltage at which switching occurs is the forward blocking voltage

Reverse Blocking Voltage The reverse blocking voltage is measured the same way as the forward blocking voltage except that the POLARITY switch is set to – (PNP).

2-31

Page 50

SIGNAL DIODES AND RECTIFYING DIODES

Required Type 576 Control Settings

Control	Required Setting
HORIZONTAL	COLLECTOR
PEAK POWER WATTS	Less than maximum power rating of device
POLARITY	+(NPN)
Terminal Selector	EMITTER GROUNDED

Some Common Measurements

IF and VF

IR and VR

To measure forward current and voltage, put the cathode of the diode in the emitter terminal of the test socket and the anode of the diode in the collector terminal. Apply voltage to the device with the VARIABLE COLLECTOR SUPPLY control.

Current and voltage in the reverse direction are measured in the same manner as in the forward direction except that the POLARITY switch is set to –(PNP). For measurements of small amounts of reverse current, set the MODE switch to LEAKAGE (EMITTER CURRENT).

ZENER DIODES

Required Type 576 Control Settings

Control	Required Setting
HORIZONTAL	COLLECTOR
PEAK POWER WATTS	Less than maximum power rating of device
POLARITY	(PNP)
Terminal Selector	EMITTER GROUNDED

Page 51

Operating Instructions-Type 576

Some Common Measurements

V_Z and I_R

To measure Zener voltage or reverse current, put the cathode of the diode in the emitter terminal of the test socket and the anode of the diode in the collector terminal. Apply voltage to the device with the VARIABLE COLLECTOR SUPPLY control. For a more accurate measurement of Zener voltage, see steps 42 through 46 of the First Time Operation instructions. For measurements of small amounts of reverse current, set the MODE switch to LEAKAGE (EMITTER CURRENT).

IF and VF

(C )

Current and voltage in the forward direction are measured in the same manner as in the reverse direction except that the POLARITY switch is set to +(NPN). For a display of currents and voltages in both directions, set the POLARITY switch to AC.

TUNNEL DIODES AND BACK DIODES

Required Type 576 Control Settings

Control	Required Setting
HORIZONTAL	COLLECTOR
PEAK POWER WATTS	Less than maximum power rating of device
POLARITY	+(NPN)
Terminal Selector	EMITTER GROUNDED

Page 52

IF and VF

Some Common Measurements

To measure the forward current and voltage characteristics of a tunnel diode or a back diode, such as the peak point and valley point currents and voltages, put the cathode of the diode in the emitter terminal of the test socket and the anode of the diode in the collector terminal. Apply voltage to the device with the VARIABLE COLLECTOR SUPPLY control. For most accurate measurements of peak and valley points, use the magnified display offset as described in steps 42 through 46 of the First Time Operation instructions.

IR and VR

Current and voltage in the reverse direction are measured in the same manner as in the forward direction except that the POLARITY switch is set to –(PNP). For a display of currents and voltages in both directions, set the POLARITY switch to AC.

Page 53

WARNING

THE FOLLOWING SERVICING INSTRUCTIONS ARE FOR USE BY QUALIFIED PERSONNEL ONLY. TO AVOID PERSONAL INJURY, DO NOT PERFORM ANY SERVICING OTHER THAN THAT CONTAINED IN OPERATING INSTRUCTIONS UNLESS YOU ARE QUALIFIED TO DO SO. REFER TO OPERATORS SAFETY SUMMARY AND SERVICE SAFETY SUMMARY PRIOR TO PERFORMING ANY SERVICE.

Page 54

Page 55

SECTION 3 CIRCUIT DESCRIPTION

General

This discussion of the Type 576 internal operation is divided into two parts: Block diagram description and circuit description. The block diagram description discusses the functions of the major circuits within the instrument, using the overall block diagram. The circuit description provides a detailed description of all the major circuits and the signal switching within the instrument.

It is suggested that the block diagrams and schematics which have been included in this manual be referred to while reading this circuit description. Individual block diagrams and simplified schematics of most of the major circuits and signal switching accompany the text of this section. An overall block diagram of the instrument, showing all the major circuits and a simplified version of the signal switching, is provided in the diagrams section at the back of the manual. Also in the diagram sections are complete schematics of all the circuitry within the Type 576 which include component part numbers and values.

BLOCK DIAGRAM DESCRIPTION

The Type 576 is a static and dynamic semiconductor tester which displays and allows measurement of static and dynamic semiconductor characteristics obtained under simulated operating conditions. The collector supply circuit and the step generator produce operating voltages and currents which are applied to the device under test. The display amplifiers measure the effects of these applied conditions. The tests result in curves of transistor, diode, and other semiconductor device characteristics traced on the face of a CRT.

The collector supply circuit produce full-wave rectified sine waves which may be either positive-going or negative-going or unrectified sine waves, depending on the position of the PO-LARITY switch. The amplitude of the signal can be varied from 0 to 1500 volts as determined by the MAX PEAK VOLTS switch and the VARIABLE COLLECTOR SUPPLY control. The Collector Supply output is applied to the collector (or equivalent) terminal of the device under test.

The step generator produces ascending steps of current or voltage at a normal rate of one step for each half-sine wave of the collector supply. The amount of current or voltage per step is controlled by the AMPLITUDE switch and the total number of steps is controlled by the NUMBER OF STEPS switch. The Step Generator output may be applied to either the base or the emitter (or equivalent) terminals of the device under test.

The display amplifiers are connected to the device under test. These amplifiers measure the effects of the collector supply and the step generator on the device under test, amplify the measurements, and apply the resulting voltages to the deflection plates of the CRT. The sensitivities of these amplifers are controlled by the VERTICAL CURRENT/DIV switch and the HORIZONTAL VOLTS/DIV switch.

CIRCUIT DESCRIPTION

The following discussion provides a detailed circuit description of all the major circuits within the Type 576 and the Standard Test Fixture. This description explains the operation of the various circuits within the instrument, and the voltages and waveforms which can be expected from them. Discussion of basic electronics and simple electronic circuits will be kept at a minimum.

Collector Supply

The collector supply circuit produces an unrectified sine wave or a full-wave rectified sine wave with a peak amplitude which may be varied from 0 to 1500 volts peak in four ranges. The initial voltage for the collector supply comes from variable auto-transformer T300 (see Fig. 3-1) which has a source voltage of 115 volts AC. The output of T300 is connected to the primary of sweep transformer T301 and is controlled by the VARIABLE COLLECTOR SUPPLY VOLTS control and varies from 0 to 115 volts. The MAX PEAK VOLTS switch allows the choice of four collector sweep voltage ranges by choosing pairs of transformer taps is rectified by one of two diode bridge rectifier assemblies: the 500 volt assembly for the 15, 75 and 350 volt ranges.

The 500 volt rectifier assembly is used either as a center tapped full-wave rectifier or a bridge rectifier depending on the connection of the current return input to the collector supply. The current return comes from the non-grounded side of the current sensing resistor. Since the voltage level of the current return input is dependent on the current flowing through the current sensing resistor, the collector supply can be considered to be floating. For the 15 volt or 75 volt ranges, the current return is connected to the center tap of the sweep transformer secondary. In this case only two diodes of the 500 volt rectifier assembly are used as a full-wave rectifier. For the 350 volt range, the current return goes to the bridge rather than the center tap of the transformer. In this case, the whole 500 volt

Page 56

Fig. 3-1. Simplified schematic of collector supply circuit

rectifier assembly is used for rectification. Operation in the 1500 volt range is similar to operation in the 350 volt range except that the 2 kilovolt bridge is used for rectification.

The POLARITY switch (see the Collector Supply schematic) allows the choice of three different sweep outputs from the collector supply by changing the output connections on the rectifier bridges. The possible outputs are positive-going + (NPN) or negative-going - (PNP) full-wave rectifed sine waves or unrectified sine-waves (AC). In all cases the peak amplitude of the collector sweep is controlled by the VARI-ABLE COLLECTOR SUPPLY control and the MAX PEAK VOLTS switch.

The MODE switch allows the choice of two different Collector Supply outputs: the normal collector sweep as has been previously mentioned and a DC collector voltage output. When the MODE switch is set to DC (ANTILOOP) or LEAKAGE (EMIT-TER CURRENT) the MAX PEAK VOLTS switch picks one of four resistor-capacitor combinations which is connected between the collector sweep output and the current return input. The purpose of these capacitors is to hold the collector sweep voltage at a constant DC level set by the VARIABLE COLLEC.

TOR SUPPLY control. This holding is done by charging the capacitor up to maximum peak voltage as set by the VARI-ABLE COLLECTOR SUPPLY control and keeping them charged with the repetitive collector sweep. The result of charging these holding capacitors is a dot on the CRT rather than the normal sweep.

In series with the collector sweep are series resitors R34 through R355. The interconnected MAX PEAK VOLTS and PEAK POWER WATTS switches add these resistors in series according to the amount of peak collector current desired. The amount of this current is determined by the maximum power dissipation rating of the device under test.

Looping

There is a certain amount of non-discrete capacitance asso ciated with the collector supply which causes an effect known as looping. Part of this undesired capacitance is stray capacitance, which provides an AC current path between the collector supply and chassis ground. The transformer and the guard box also exhibit some undesired capacitance between the guard box potential (common return point connected to guard

Page 57

Fig. 3-2. (A) Undesired capacitance causing looping; (B) Looping compensation.

box) and chassis ground. Fig. 3-2A shows that these two capacitances form a divider from AC current, the center of the divider being connected to the vertical amplifier.

During transitions of the collector sweep, some current will be transmitted by this undesired capacitance, bypassing the device under test. This current, however, is sensed by the vertical amplifier along with the collector current and causes the reading of collector current on the CRT to be incorrect. When the collector sweep rises, the undesired current will start positive and decrease to zero as the collector sweep reaches its peak. As the sweep falls, the stray current will go negative. The result on the CRT is a loop instead of a single line to represent the curve of lo vs Voc.

Looping Compensation

The LOOPING COMPENSATION adjustment, C343 (see Fig. 3-2B and the Collector Supply schematic), H.F. NOISE REJEC-TION adjustment C341 and R414 through R418 (see the Display Sensitivity Switching schematic) have been added to the circuitry as compensation for the stray and guard box capacitance previously discussed. In general, these adjustments will

not compensate for device capacitance. This added capacitance forms a new capacitive divider which transmits AC current to the vertical amplifier in opposition to the current transmitted by the undesired capacitance. This opposing current, therefore, nulls the effect of the undesired capacitance which causes looping. In adjusting these added capacitors, C343 is adjusted to compensate for looping current transmitted from the collector sweep to ground, and C341 is adjusted to compensate for high frequency noise coming in on the line.

Another source of looping current is unbalance in the sweep transformer. As has been discussed in the collector supply circuit description, the sweep transformer is sometimes used in a full-wave rectifier arrangement. This method of transformer operation requires that the transformer be balanced about the center tap. LOOPING BALANCE adjustment C301 is adjusted to equalize the capacitance on both sides of the transformer center tap.

When the transformer is used in bridge operation, the voltage at one end is held essentially constant, and the transformer operates unbalanced. In this case, the transformer capacitance is added to the stray capacitance found between

Page 58

the Collector Supply and ground. 350 V and 1500 V LOOPING COMP adjustment C339 has been added between the transformer center tap and the junction of C343 and C341, for bridge operation of the Collector Supply to compensate for unbalanced operation of the transformer.

Interlock

The Type 576 has an interlock system designed to protect the user of the instrument from potentially dangerous voltages which may appear at the Collector terminals of the Standard Test Fixture. The interlock system is shown on the Collector Supply schematic in Section 8.

Coil K323 enables or disables the Collector Supply output through K323-B, enabling it when the coil is energized. The coil is always energized when the MAX PEAK VOLTS switch is set to 15. When this switch is set to the 75, 350 or 1500 positions, one side of the coil is opened and the Collector Supply is diabled. The yellow COLLECTOR SUPPLY VOLTAGE DIS-ABLED light is turned on through K323-A. In order to enable the Collector Supply under these conditions, the Protective Box must be put in place on the Standard Text Fixture and the lid closed. With the lid closed, High Voltage Interlock switch SW360 is closed and +12.5 volts is applied through the red DANGEROUS VOLTAGE light, B360, to coil K323, thus enabling the Collector Supply. With the coil now activated, the COLLECTOR SUPPLY VOLTAGE DISABLED light is turned off.

The COLLECTOR SUPPLY VOLTAGE DISABLED light may also be turned on if thermal cutout TK346 becomes open. TK346 opens whenever the internal heat in the instrument becomes hot enough to damage the collector supply or the readout

Step Generato

The purpose of the step generator is to present a discrete level of current or voltage to the base or emitter (or equivalent terminals) of the device under test for each sweep, or change of direction of sweep, of the collector supply. These discrete levels are generated in the form of ascending steps which have a calibrated current or voltage separation.

The step generator circuit consists of four major sections: the clock, the counter, the digital-to-analog converter, and the pulsed steps operation section. The clock circuit produces negative-going clock pulses which determine the rate and phase, with respect to the collector supply, of the Step Generator output. The counter circuit counts these clock pulses and transforms each count into a digital code which controls

the digital-to-analog converter. The digital-to-analog converter transforms the digital code into analog current which is summed at a current summing node and transmitted to the step amplifier. The pulsed steps operation circuit provides a variation of the Step Generator output where short duration pulsed steps rather than normal steps are generated.

Logic. The clock circuit, the counter circuit and a portion of the digital-to-analog circuit are digital circuits which make use of transistors and integrated circuits in digital configurations. The most convenient method of describing and understanding digital circuitry is through a logic description rather than a detailed circuit description. In order to make this description understandable by a wider range of readers, a simplified logic description, using high and low rather than true and false, has been utilized. A knowledge of basic logic symbols and truth tables will help in understanding this description.

Simplified schematics of each of these circuits are shown in Figs. 3-5, 3-6 and 3-7. Pertinent information such as internal logic diagrams, truth tables, timing charts and descriptions of operation are given in Fig. 8-1 at the beginning of the Diagrams section, for all the logic devices used in the Step Generator circuit. Logic level information for these logic devices is shown in blue on the Step Generator schematic. Familiarity with the logic symbols and related truth tables of these logic devices will greatly aid in understanding the following description.

Clock. Sine waves produced at line frequency by trans former T701 provide the timing source for the clock (see the Step Generator schematic) Transformer T701 steering diodes D1-D2 and D10-D11, and trigger generators U3A-U3B and U3C LI3D operate together to produce low level pulses at the inputs of 1224 Using 134-138 as an example, each time the trans former voltage at the anode of D1 crosses zero going negative D1 will turn off and D2 will turn on When D2 is conducting the voltage at the pin 1 input of USA is held at a low voltage level Since the other input to U3A, pin 2, is held at a high voltage level by voltage divider R4-R5, this low causes a high to appea at the output of USA (see Fig. 8-1 at the beginning of the Diagrams section for truth table of inverted input OR gate This high is inverted by U3B and the resulting low is applied to the pin 1 input of LI22A. This low output produced by the tri ger generator continues until C5 charges to a high voltage leve as determined by divider R4-R5. When the voltage at D crosses through zero going positive. D1 turns on and D2 turns off With D2 off both inputs to U3A are high the output goes low and the output of USB goes high. This is the guidegoes state of the trigger generator. Trigger generator U3D-U3C on state of the ingger generator. Ingger generator USU-USU op pin 9 of U3C allows the trigger generator to be inhibited when low is applied to i

Page 59

3-5

Page 60

Transformer T701 (see Fig. 3-4) is center tapped, causing the voltages at its outputs to be equal and opposite. The two trigger generators are triggered by T701, therefore, operate in opposite phase, producing alternate low level pulses at their outputs. Since T701 is in phase with the Collector Supply output, a pulse is generated by one of the trigger generators at the start of each collector sweep (assuming + NPN or - PNP polarity). ZERO CROSS adjustment R8 allows adjustment of the trigger level of the trigger generators.

With the NORM RATE button pressed, low pulses from the trigger generator are inverted to U22A and transmitted to norm pulse gate U22B. The pin 5 input to U22B is normally held high. A high at its other input, therefore, produces a low at its output. This low is applied to U22C, which produces a high level clock pulse to be applied to the counter circuit. With the NORM RATE button pressed, the rate of production of clock pulses (and therefore the step generator rate) is 120 pulses/second (assuming a 60 Hz line frequency) which is the normal collector supply rate.

High level output pulses from U22A are also applied to the base of O23 (shown on the Step Generator schematic) the input to the delay circuit. This circuit generates clock pulses at the normal rate, but delayed (with respect to the start of each normal clock pulse) by a delay time equal to half the time duration between normal clock pulses. This delay circuit is trig gered each time a high is produced at the output of U22A. This high turns on O23 which nulls down on the base of O30 turns ing it off. Since O23 is pulling down on one side of C26, the other side begins charging. It continues to charge until a high enough voltage is reached to again turn on Q30. When Q30 turns on a low level is produced at its collector which is differentiated by C33 and B33 into a negative-going spike and applied to the input of inverter U33A. The result of this low at the input of U33A is a high at its output, and thus a high-level delayed pulse at the pin 13 input of 1 122D. The delay time of the half-step delay circuit is controlled by DELAY adjustment B24 which controls the charge time of C26 B24 is adjusted for a delay time equal to half the duration of a normal step (about 4167 us) Delayed clock pulses therefore occur coincident with the peak of the Collector Supply output, SW27 lengthens the delay time of this circuit to 5000 us when T701 is operated with a EQ Ha line frequency

The clock circuit has two sources of clock pulses, the output of U22A and the output of the delay circuit. The various step generator rates are produced by inhibiting some of the clock pulses from these two sources from being summed by U22C. Three devices control the transmission of clock pulses through the circuit: Trig Gen Gate U20C, Norm Pulse Gate U22B and Delayed Pulse Gate U22D

When the NORM RATE button is pressed, pin 9 of U3C is held high, enabling trigger generator U3D-U3C. A high is also applied to pin 5 of U22B, allowing the clock pulses from U22A

to be transmitted to pin 9 of U22C. A low is applied to pin 12 of U22D, inhibiting the delayed clock pulse. When the 5X RATE button is pressed, the circuit operates as described for normal operation except that both inputs of U20C are held high, which holds nin 9 of LI3C low and inhibits trigger generator U3C-U3D The result is a step generator rate of half the normal rate, 60 steps/second (assuming a 60 Hz line frequency). Pressing the 2X RATE button causes normal operation of the circuit, except that a high is applied to pin 12 of U22D allowing the delayed clock pulses to be applied to pin 10 of U22C. The step genera tor rate in this case is 240 steps/second. When both the 2X BATE and the 5X BATE buttons are pressed, the normal clock pulses are inhibited by a low at pin 5 of LI22R and the delayed clock pulses are transmitted to U22C. In this case the Step Generator rate is normal, but the steps occur out of phase with the normal steps by the delay time of the delay circuit

Counter. When the clock circuit generates a clock pulse, if is counted by the counter (see Fig. 3-5). The counter counts clock pulses until it reaches a preset number, then resets and begins counting again. Each time the counter counts, if changes a four-bit binary code which is applied to the digital to-analog converter.

U70 is a divide-by-16 counter with the outputs of all four of its internal flip-flops utilized (see Fig. 3-5). A negative pulse at the pin 14 input of U70 causes a count to be recorded by the flip-flops. In recording a count, the flip-flops assume high or low states according to a 1-2-4-8 binary code. A high state represents the presence of either a 1, 2, 4 or 8. A low state represents a 0. Output terminals 12, 9, 8 and 11 of U70 represent 1, 2, 4 and 8 respectively. By connecting pin 8 and pin 11 of U70 to U72D through inverters, the 1-2-4-8 code of the U70 outputs is modified to a 1-2-4-4 code. The truth table in Table 3-1 shows the state of each modified counter output for successive counts counted by U70 up to 11. Whenever U70 is reset, it returns to the zero count state with lows on all the outputs.

The counter may be report after from 1 to 10 stops have been produced. The NI IMBER OF STEPS switch determines on which cleak pulse the counter is reset. This switch presets the inputs to U75 so that when the counter has counted the de sired number of clock pulses, a bight is generated at pins 2 and 3 of U70, resetting the counter. This high is generated when a high appears at the output of reset trigger generator 1175, 1175 consists of four inverted input OR gates whose outputs are connected to a 4-input AND gate. One input of each inverted input OP gate is connected through an inverter to an output of the modified counter. The other input is connected to a section of the NI IMBED OF STEPS switch When a low appears on one input of each inverted input OR gate of U75, all four inputs to the LI75 AND gate will be low and a high reset pulse is produced at the output. This condition of having at least one low on each inverted input OR gate of LI75 is typically obtained by first setting lows on some of the inverted input OR gates through the NUMBER OF STEPS switch The counter then counts until lows are produced by the modified counter output at the inverted input OR gates without preset lows. When no at the inverted input on gates without preset lows, when he or preset lows are applied to 1175, the counter is reset when it

Page 61

Page 62

reaches the eleventh step (1 + 2 + 4 + 4 = 11) when all modified counter outputs are low. It should be noted that the clock pulse which causes the counter to be reset is always one clock pulse more than the number selected by the NUMBER OF STEPS switch. The time duration from the point at which this extra clock pulse is counted by the counter to the point when the counter is reset is so short that the extra step never appears at the Step Generator output.

The high at the output of U75 is inverted by U33B (see the Step Generator Schematic) and again by U69C, producing a reset high at pin 2 and 3 of U70. U71D and C81 stretch the reset high to a long-enough duration to assure that the counter is reset.

The state of pin 2 of clock pulse enable U69A determines whether clock pulses are applied to the pin 14 input of U70. When the STEP FAMILY REP button is pressed, a low is applied to pin 5 of U69B, causing pin 2 of U69A to be held permanently high. In this state of U69A, all clock pulses applied to its pin 1 input are inverted, and become counter triggers. When the STEP FAMILY SINGLE button is pressed, a momentary low is applied to pin 5 of U69B which goes high as C78 charges. This momentary low enables U69A until one step family has been generated. When the reset high causes pin 4 of U69B to go high, a low is produced at the pin 2 input of U69A. This low inhibits clock pulses from being transmitted past U69A.

Digital-to-Analog Converter. The outputs of them modified counter are connected to the digital-to-analog converter. The purpose of this circuit is to convert the modified counter output code into analog current which is applied to the step ampiifier input. The digital-to-analog converter consists of a set of current setting resistor pairs and four sets of current steering diodes.

TABLE 3-1

Normal and Modified Counter Output Codes

Count		Normal Code			Modified Code
		Pins on U70			Pins on U70			U72D
	12	9	8	11	12	9	11	11
0	L	L	L	L	L	L	L	L
1	н	L	L	L	Н	L	L	L
2	L	н	L	L	L	н	L	L
3	Н	н	L	L	Н	Н	L	L
4	L	L	Н	L	L	L	L	н
5	Н	L	Н	L	н	L	L	Н
6	L	н	н	L	L	н	L	н
7	н	н	Н	L	Н	Н	L	н
8	L	L	L	Н	L	L	Н	Н
9	н	L	L	Н	Н	L	н	Н
10	L	н	L	Н	L -	Н	н	Н
11	н	н	L	Н	Н	Н	Н	н

The digital-to-analog converter conducts a constant amount of current, the amount of which is set by current setting resistor pairs R54-R55, R57-R58, R60-R61 and R63-R64 (see Fig. 3-6). Each resistor pair conducts a discrete amount of current which is a multiple of the modified counter code: one increment of current conducted by R54-R55, two increments by R57-R58, four by R60-R61 and four by R63-R64. Each increment of current causes one step to be generated at the Step Generator output.

Another set of current paths is provided by diodes D54 D57, D60 and D63. These diodes provide current paths be tween the current summing node (at the cathode of D83)

Page 63

Fig. 3-6. Simplified schematic of Digital-To-Analog Converter.

10.0

Page 64

and the current setting resistor pairs. It is these current paths which cause step current to be conducted by the step amplifier input. Whenever a high appears at one of the modified counter outputs, its associated steering diode off and the current conducted by its associated resistor pair is conducted by the step amplifier input.

The amount of current conducted by the step amplifier input is a function of the modified counter output and may be determined by adding the currents conducted by each resistor pair associated with a modified counter output which is high For example if five counts have been recorded by the counter, highs appear at the cathodes of D70 and D72 The current applied to the step amplifier input is, therefore, one increment by R54-R55 plus four increments by R60-R61, totalling 5 increments. Thus five counts recorded by the counter results in five increments of analog current conducted by the step amplifier input The 1-2-1-1 modified counter code is designed so that the step current conducted by the step amplifier input in creases by one increment for each clock pulse counted by the counter (until the counter resets). ZERO STEP adjustment B97 controls the level of the zero step (with zero offset) by adjusting the quiescent current through D82 and D83

Steering diodes D66, D67, D68 and D69 provide current paths for the currents conducted by R55, R58, R61 and R64, respectively, whenever the STEP MULT .1X button is pressed. (With the STEP MULT .1X button pressed D55, D58, D61 and D64 are reverse biased.) These new current paths reduce the amount of current per increment which may be conducted by the step amplifier input by a factor of 10. The result is that the step amplitude is reduced to one-tenth its normal value.

The fourth set of steering diodes, D41, D42, D43 and D44 is used only when the step generator is operating in the pulsed mode. In all other cases, their cathodes are held high and they have no effect on the current applied to the step amplifier input.

The current summing node sums current from R95 as well as the digital-to-analog converter. The zero step leve may be offset either in the direction which steps are ascend ing or in the opposite direction of ascent as deter mined by the DC current conducted by R95. If offset in the direction of the store is desired the ALD OFFSET button is pressed. This allows positive voltage to be applied to the base of O90 using the OEESET MULT control which raises the emitter voltage of 093 and causes additional current to be conducted through R95 When the OPPOSE OFFSET button is pressed preative voltage is applied to the base of OQO using the OFFSET MULT con trol which courses current to be conducted through POE in the opposite direction OPPOSE OFFSET adjustment B85 and AID OFFSET adjustment B86 adjusts the offset level of the steps when the OPPOSE OFFSET and AID OFFSET buttons are pressed respectively

Pulsed Step Mode. When one of the PULSED STEPS buttons is pressed, the Step Generator output steps are reduced to short pulses. These pulsed steps are obtained by inhibiting the digital-to-analog converter for all but 300 µs or 80 µs of each step.

The digital-to-analog converter is inhibited by pressing aither the 300us or the 80 us PUL SED STEPS button (see the Step Generator schematic) Pressing one of these buttons turns 041 on and provides current paths for the resistor pairs through D41 D42 D43 and D44 The digital to-analog converter is inhibited in this state because no step current is available to be conducted by the step amplifier input, regardless of the condition of the modified counter output. The digital-to-analog converter remains inhibited until a negative-going trigger from the collector of 0.30 reverse biases D39 and turns off O41 With O41 off its col lector roles high turning on O36 and reverse biasing steering diodes D41 D42 D43 and D44 The digital-to-analog converter is now enabled and free to produce a step in the manner described previously. The duration of the step is controlled by the charge time of C35 With O36 on its collector holds one side of C35 at about ground allowing the other side to be charged through B39 (and B37 when the 300 Us button is pressed) C35 charges until D39 is forward biased and 041 again turns on With 041 on 036 is turned off and the digital-to-analog converter is again inhibited by the steering diodes D41 D42 D43 and D44

Since each pulsed step is triggered by a negative-going trigger from the delay circuit, the pulsed steps always appear at the peak of the Collector Supply output. When the step generator is operating in the pulsed step mode, the 2X RATE button is inhibited.

When Q41 is turned on, Q46 is turned off, which also turns off Q52. The collector of Q52 is connected to the grid of the CRT, V897 (see the CRT Circuit schematic) When Q52 turns off, its collector voltage goes negative causing the intensity of the CRT display to be reduced. The display intensity remains reduced until Q41 turns off allowing Q46 and Q52 to turn on. The CRT display in the pulsed step mode is, therefore, intensified only when a pulsed step occurs

The Collector Supply schematic shows that when either the 300 µs or the 80 µs PULSED STEPS button is pressed K320 is energized and the Collector Supply operates in its DC mode. It also shows, that if the 300 µs and 80 µs PULSED STEPS buttons are pressed together, 300 µs pulsed steps are generated and the collector supply operates in its normal mode (K320 is not energized).

Step Amplifie

The step amplifier transforms the output of the step generator into current or voltage steps of various amplitudes to be applied to the device under test. The AMPLI-TUDE switch, which is part of this circuit, determines the amplitude of the steps. The circuit consists of a current to voltage converter an inverter and a differential output

Page 65

amplifier. The output amplifier has two modes of operation, one producing current steps and the other producing voltage steps.

The output of the Step Generator, which may be from one to ten current steps of 350 µA per step plus from one to ten steps of offset, is applied to the base of Q105A (see the Step Amplifier schematic). Q105A together with Q105B form a differential amplifier. As the base current of Q105A is decreased, the collector current of Q105B increases, raising the voltage at the base of Q110. Each current step at the base of Q105A, therefore, causes a positive voltage step at the base of Q110 which is amplified and inverted by Q110. Part of the output of Q110 is transmitted through R113, R112 and C112 creating negative feedback at the base of Q105A. R113 adjusts the feedback gain of current to voltage amplifier Q105 and Q110 for an output at the collector of Q110 of negative-going steps with amplitudes of 1/2 volt/step.

Q117 and Q122 have been added to the current to voltage amplifier circuit to slow down the voltage transition from the level of the last step generated to the zero step level, in cases where this transition may cause damage to the device under test. When the preset number of steps has been produced at the Q110 output, a rapid transition occurs as the step returns to its starting point. This transition, when applied to the base of a transistor, rapidly turns it off. If a transistor is turned off in this manner when its collector is at a high level, a high inductive voltage kick will be produced in the collector supply transformer. Such an inductive voltage kick may be large enough to damage the transistor.

This circuit operates either when the 2X RATE button is pressed or when the 300 us and 80 us PULISED STEPS buttons are pressed together. In this case the emitter circuit of 0122 is opened, turning the transistor off. The source of EFT 0117 is held at -11.3 volts by divider B116-D115-B108 When O122 turns off, divider B119-B120-B121 sets the voltage at the gate of O117 at -10.3 volts, turning the FET on. With Q117 on, its drain is held at about -11.3 volts providing a constant voltage on the side of C114 connected to Q117. By holding one side of C114 at constant voltage and transmitting the output of 0110 across the other side C114 becomes an integrator The voltage transition of the O110 output from the level of its last step to the starting level is therefore, slowed down by integrator C114 When O122 is turned on (normal or 0.5 times rate or DC mode) 0117 is held off by having about -34 volts at its gate. In this case, the current through R117 controls the voltage on Q117 side of C114, which moves up and down with changes in the output of Q110. C114. therefore has little effect on the output of Q110 and causes no slowing of the voltage transition.

When relay K101A is in the – position, the output of Q110 is transmitted through inverter circuit Q130A and B and Q133 and inverted before it is applied to the output

amplifier. The inverter is identical in operation to the current to voltage amplifier described previously. Since the input resistance (R125) and the feedback resistance (R137) are equal, the gain of the inverter is 1. INVERT ZERO adjustment R127 sets the voltage at the base of Q130A so that the initial level is the same for the non-inverted steps and the inverted steps.

The position of relay K101A is controlled by the COL-LECTOR SUPPLY POLARITY switch, the STEP-OFFSET POLARITY INVERT button and the Terminal Selector switch in conjunction with the step generator polarity logic (see the Step Amplifier schematic) 1133C and D 1172A B and C form a coincidence gate. See Table 3-2 for a truth table of this gate. The output at pin 6 of U72B causes O101 to turn on and off thus switching relay K101A between + and - If a high appears at the output of U72B_K101A switches to the – position and if a low appears, it remains in the + state. The inputs to U33C and D and to U72A and C are controlled by the voltage levels on connectors T and S as shown in Table 3-2. Setting the Terminal Selector switch to EMITTER TERM STEP GEN has the same effect on the voltage level of connector T as pressing the POLABITY INVERT button If the POLARITY INVERT button is pressed, however, the Terminal Selector switch has no effect on the voltage level at connector T and vice versa.

TABLE 3-2

Step Generator Polarity Logic

COLLECTOR		Conn	Din 6
	INVERT	т	s	U72B
AC	Pressed	Н	L	Н
AC	Not Pressed	Н	н	L
+(NPN)	Pressed	Н	L	Н
+(NPN)	Not Pressed	Н	н	L
-(PNP)	Pressed	L	L	L
-(PNP)	Not Pressed	L	Н	Н

Output Amplifier The step output amplifier transforms the output steps of the current to voltage amplifier (or inverter) into current or voltage steps of various amplitudes as determined by the AMPLITUDE switch. It is basically a differential amplifier with separate feedback to each input. The negative input side of the amplifier controls the amplitude of the output steps. The positive input side of the amplifier provides either current regulation or a constant operating level To obtain current steps (see Fig. 3-7A) the gain of the negative side of the differential amplifier is set for an output of 1 volt per step. This output is then transmitted through a variable resistance in series, the current setting resistors. With the constant voltage per step relationship across the current setting resistors, the current per step output can be varied by changing this resistance in series To obtain voltage steps, the input resistance to the nega-

Page 66

Circuit Description-Type 576

Fig. 3-7. Block diagram of Step Output Amplifier: (A) Current Mode; (B) Voltage Mode.

tive input, the voltage setting resistors, is changed, thus varying the feedback gain of that side of the differential amplifier. In this manner voltage steps of various amplitudes are obtained.

Current Mode. Input to the negative side of the differential comparator, at the base of 0150A, is always through VOLTAGE SETTING RESISTORS R141 through R145. In the current mode, this input resistance is set at 3.01 kΩ (B141) for all current positions of the AMPLITUDE switch. When 1/2 volt steps are applied to the base of O150A through R141, they are inverted, applied to the base of Q164 and inverted again. The steps are then transmitted through emitter follower Q169 to the bases of Q172 and Q176. Depending on the position of relay contacts K102B and K102C, either Q172 and Q180 or Q176 and Q184 are turned on. If, for example, K102B and K102C are in the + positions, signifying positive-going steps out, Q176 and Q184 are on the Q172 and Q180 are off. In this case the input to Q176 is negative-going steps. They are inverted by Q176 and the resulting positive-going steps are transmitted through emitter follower Q184 to the negative side of the floating 50-volt supply. Each time a positive step occurs at the negative side of the 50-volt supply, the supply

is pushed up by the amount of the step. The positive side of the 50-volt supply is connected to both the feedback resistors and the input to the current setting resistors, so that each time the 50-volt supply is raised by a step, the voltage at this connecting point is also raised by the amount of the step. Due to the presence of the 50-volt supply, the voltage at the input to the current setting resistors is offset by 50 volts. To compensate for this offset, 50 volts of opposing offset is added to the input of the current setting resistors through relay K102A. If K102B and K102C are in their positions, Q172 and Q180 are on and Q176 and Q184 are off. In this case negative-going steps are applied to the positive side of the 50-volt supply and negative-going steps appear at the input to the current setting resistors.

The output of the negative side of the differential amplifier at either K102B or K102C is fed back to the base of Q150A through feedback resistor R194. Since R194 is 6.04 kΩ and the input resistance, R141, is 3.01 kΩ the feedback gain of this circuit is 2. For a half volt per step input, the resulting output of the negative side of the differential amplifier (as seen by the input to CURRENT SETTING RESISTORS R197 through R216) is steps of one volt per step, the zero level being at ground. (If offset has been

Page 67

added in the step generator circuit, the zero step level may range from 0 to 10 volts.)

The output end of the current setting resistors is connected through the device under test to ground. When voltage steps of 1 volt per step are applied between the input end of the current setting resistors and ground, current steps of variable amplitude flow through the device under test. The current amplitude of the steps is determined by AMPLITUDE switch SW195 (see Step Generator Switching schematic), which chooses various combinations of resistors R197 through R216.

In order to obtain calibrated current steps, the voltage across the current setting resistors must be held at 1 volt per step. The voltage at the output, however, may vary by the amount of the turn-on voltage of the device under test thus altering the current per step output of the step generator. To compensate for this turn-on voltage, any variation from ground of voltage at the input to the device under test is transmitted through the +1 amplifier to the positive side of the differential amplifier. This starts a regulating process which causes the voltage at the input to the current setting resistors to move in the same direction as the turn-on voltage at the output, thus nullifying its effect.

The +1 amplifier is made up of paraphase amplifier 0220A and B constant current sources 0233 and 0226 and emitter followers Q235 and Q241. In the current mode, any voltage at the input of the device under test is transmitted through R220 to the high impedance gate input to Q229B. If, for example, this variation is a rise in voltage at the gate input, it will be accompanied by a rise in voltage at the drain of Q229A, due to the paraphase operation of 0229A and B. Baising the voltage at the 0229A drain raises the base of emitter follower 0235 and thus the base of emitter follower 0241 As the emitter of 0241 follows its base up, it pulls the voltage at the gate of 0229A up so that it is equal to the voltage at the gate of Q229B. This rise in voltage at the gate of O229A is then transmitted to the base of O150B (positive side of the differential amplifier) through feedback resistors R243 and R244. The +1 amplifier, therefore, transmits any voltage variation from the input to the device under test to the input to the base of O150B with no change in amplitude or polarity. In performing this task, the +1 amplifier provides the voltage variation with a high impedance input and a low impedance output. When the rise in voltage at the base of 0150B has been transmitted to the input to the current setting resistors it compensates for voltage variations at the input to the device under test holding the voltage across the current setting resistors at 1 volt per step. AMP BAL adjustment R224 adjusts the DC balance of paraphase amplifier Q229, and also compensates for unbalance in 0150 OUTPUT Z adjustment R243 adjusts the output impedance of the step amplifier

Relay K101B and Q248 or Q250 are used to limit the voltage which may be applied to a device under test in the reverse direction using opposing offset. If, for example,

positive going steps are to be applied to the device under test, K101B is in the + position. If negative offset is applied to the device under test by pushing the OPPOSE button and turning the OFFSET MULT control clockwise, the step generator will attempt to conduct negative current at the input to the device under test. In doing this, the voltage at the input to the device under test and thus the voltage at the Q229B gate input is driven down. When the voltage goes approximately 2 volts below ground, Q248 turns on. With Q248 on, the negative-going voltage steps at the base of Q150A are limited, thus limiting the output of the output amplifier (the input to the device under test) to about 2 volts. This amount of voltage should not damage a device under test.

Voltage Mode. Voltage steps are obtained from the output amplifier in a manner similar to that used to obtain current steps. For voltage steps, however, the VOLTAGE SETTING RESISTORS are changed to obtain the various voltage amplitudes, rather than the CURRENT SETTING RESISTORS (which are held constant in the voltage mode). Also since it is not desirable to regulate the voltage at the input to the CURRENT SETTING RESISTORS in the voltage mode, the feedback to the positive side of the differential amplifier through the +1 amplifier is disconnected and the input to the +1 amplifier is connected to ground. The base of Q150B is, therefore, held at essentially ground. Since the output of the +1 amplifier is at ground, reverse voltage limiting transistors Q248 and Q250 are disabled in the voltage mode.

In the voltage mode when steps of 1/2 volt per step are applied to the step output amplifier, they are transmitted through VOLTAGE SETTING RESISTORS R141 through R145, the input resistance. By varying this input resistance with respect to constant feedback resistor R194, the feedback gain of the negative side of the differential amplifier is changed, thus varying the amplitude of the voltage steps. After being conducted through the voltage setting resistors, the steps are amplified and transmitted through the negative side of the differential amplifier in the same manner as described in the current mode section. When the voltage steps reach the CURRENT SETTING RESISTORS, they are transmitted through a nominal resistance (R215 and R216) of 5 Ω, for all voltage positions of the AMPLITUDE switch before being applied to the device under test. Voltage steps of varying amplitudes, as determined by the AMPLITUDE switch, are then applied across the input impedance of the device under test. Feedback to the input to the differential amplifier occurs at the output of the current setting resistors, therefore, minimizing the effect of R215 and R216.

When using voltage steps, the current conducted at the step generator input to the device under test may increase quite rapidly and possibly damage the device under test (especially when testing transistors). As a means of limiting this current in the voltage mode, current limiting resistors R185, R186 and R187 are added to the output amplifier circuit by the CURRENT LIMIT switch. These resistors limit current at the Step Generator Output by limiting

Page 68

Fig. 3-8. Simplified schematic of Display Sensitivity Switching and Standard Test Fixture schematics for measurement of collector current (I_C) and collector-emitter voltage (V_CE) or collector-base voltage (V_CB).

Page 69

current through R165. R166 and R167. As the voltage steps increase through 0176 and 0184 or through 0172 and Q180, the current increases through the current limiting resistors. This current increase causes the voltage drop across the resistors to increase. If positive-going steps are being produced, this increase in voltage drop is transmitted through Q176 and Q169 to the junction of R166 and R167. As the voltage drop increases, the voltage at this junction point does down. When the voltage reaches about -2.3 volts D165 forward biases clamping the voltage at the base of 0169 This prevents generation of further steps When negative-going steps are being produced, the drop across the current limiting resistors is transmitted through three baseemitter junctions. 0180. 0172 and 0169. to the junction of R166 and R167. As voltage drop increases, the voltage at the collector of Q164 goes up. When this voltage reaches +12.5 volts 0164 is saturated and again no further stops can be generated. The CUBBENT LIMIT switch determines the number of resistors to be included in the current limiting resistance, therefore determining the amount of current necessary to either turn on D165 or saturate 0169

VERTICAL AND HORIZONTAL DISPLAY Signal Sensing and Display Sensitivity

Once the Collector Supply and the Step Generator Output have been applied to the device under test, measurements of the voltages and currents seen at the terminals of the device under test may be displayed on the vertical and horizontal axes of the CRT. These measurements are made by first sensing the current or voltage through current sensing resistors or voltage dividers, then amplifying the resulting voltage with the display amplifiers and applying them to the deflection plates of the CRT. The positions of the HORIZONTAL, the MODE and the Terminal Selector switches determine which measurements are made.

Collector Current Sensing. If the MODE switch is set to either NORM or DC, collector current (I_C) is measured on the vertical axis of the CRT. Collector current is measured by placing a resistor (R_s) between ground and the current return to the collector supply and measuring the voltage developed across this resistor (see Fig. 3-8 and Fig. 3-9). By

Fig. 3-9. Simplified schematic of Display Sensitivity Switching and Standard Test Fixture schematics for measurement of collector current (Ic) and base emitter voltage (VBB) or emitter-base voltage (VBB).

Page 70

Fig. 3-10. Simplified schematic of Display Sensitivity switching and Standard Test Fixture schematics for measurement of emitter current (IE collector-base current (ICBO) collector-emitter voltage (VCF) or collector-base voltage (VCR).

varying the value of this current sensing resistor (R_s), the deflection factor of the display on the CRT may be varied

Leakage Current Sensing. If the MODE switch is set to LEAKAGE, emitter current (IE) or collector-base current (ICBO) is measured on the vertical axis of the CRT. Emitter current is measured by placing a leakage current sensing resistance (RL) between the emitter terminal of the device under test and ground, and measuring the voltage developed across it (see Fig. 3-10). If emitter current is to be measured, the Terminal Selector switch must be set to GROUNDED EMITTER BASE TERM OPEN or BASE TERM SHORT. When the Terminal Selector switch is set to BASE GROUNDED EMITTER TERM OPEN, collectorbase current is measured on the vertical axis. In this case the current sensing resistor is connected between the base terminal and ground. As when measuring collector current the deflection factor of the display, when measuring emit

ter current and collector-base current, can be varied by varying the current sensing resistance. It should be noted that the deflection factor of the vertical display is always decreased 1000 times when the MODE switch is set to LEAKAGE and the collector supply operates in its DO mode.

Voltage Sensing Normal Mode. Either collector or base voltage may be measured on the horizontal axis of the CRT, depending on the position of the HORIZONTAL switch. When the HORIZONTAL switch is in its COLLECTOR range, voltage is measured between the collector and emitter terminals of the device under test, VCE (Terminal Selector switch set to EMITTER GROUNDED), or between the collector and base terminals, VCB, (Terminal Selector switch set to BASE GROUNDED). When the HORIZON TAL switch is in its BASE range, voltage is measured between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the base and emitter terminals, VBE (EMITTER GROUNDED), or between the device terminals, VBE (EMITTER GROUNDED), or between the device terminals, VBE (EMITTER GROUNDED), or between the device terminals, VBE (EMITTER GROUNDED), or between the device terminals, VBE (EMITTER GROUNDED), or between the device terminals, VBE (EMITTER GROUNDED), or between the device terminals, VBE (EMITTER GROUNDED), or between terminals, VBE (EMITTER GROUNDED), or between terminals, VBE (EMITTER GROUNDED), or between terminals, VBE (EMITTER GROUNDED), or between terminals, VBE (E

Page 71

V_BE (BASE GROUNDED). It should be noted, that the measurement of voltage from the emitter terminal to the base terminal appears as a negative measurement on the CRT graticule. It is not, however, a reverse voltage measurement. By use of a variable voltage divider across these terminals, the deflection factor of the horizontal display can be varied.

Voltage Sensing Leakage Mode. When the MODE switch is set to LEAKAGE, only the measurement of VCE and VCD are useful. In this situation a slight error in voltage measurement occurs whenever the VERTICAL switch is set within the 500 nA to 1 nA EMITTER range. In this range (see Fig. 3-10) the borizontal display is a measurement of collector voltage to ground, rather than collector to emitter or collector to base voltage. As discussed previously, when current measurements are made in the leakage mode the current sensing resistor is between ground and the emitter or around and the base terminal. Any measurement of voltage between the collector and ground, therefore, measures the voltage dron across the current sensing resistor and adds it to the desired measurement of Vor or Vor. The correct values of VCE or VCB can be determined by subtracting the voltage drop across the current sensing resistor from the total measurement shown on the horizontal axis of the CRT See the Horizontal Measurement and Deflection Eactor section of the Operating Instructions for instructions on how to determine this error voltage

Display of Step Generator. If either the VERTICAL or the HORIZONTAL switch is set to STEP GEN, the 1/2 volt steps at the input to the output amplifier section of the step amplifier (see Fig. 3-7) are applied to the inputs to the vertical display amplifier or the horizontal display amplifier (see Fig. 3-11). If both switches are set to STEP GEN, the 1/2 volt steps are applied to the Horizontal Display Amplifier only.

Vertical and Horizontal Positioning

The positioning of the display on the CRT is determined by current applied to the low impedance inputs of the Display Amplifiers at the emitters of Q533A and B in the vertical display amplifier, and Q633A and B in the horizontal display amplifier (see discussion of Display Amplifiers). This current comes from many individual current sources which are controlled by the POSITION switches, the FINE POSITION controls, the POLARITY switch and the DIS-PLAY OFFSET controls (see the Display Positioning schematic).

The POSITION switches and the FINE POSITION controls allow both coarse and fine positioning of the display. The current for the coarse control comes from resistors R480 through R483 (vertical) and R490 through R493 (horizontal). These resistors are all connected to the -75 volt supply, making them current sources. Each of these current sources is connected between a pair of contacts. When one contact of a pair is closed, this current flows into one side of the display amplifier. If the other contact of the pair is closed, the current flows into the other side of the amplifier. The matrixes for the POSITION cam switches show that at all times one contact of each pair must be

Fig. 3-11. Simplified schematic of Display Sensitivity Switching when VERTICAL and/or HORIZONTAL switches are set to STEP GEN.

closed, but never both closed at once. This assures that the sum of the positioning current flowing into the amplifiers is always a constant. Each POSITION switch provides 20 divisions of positioning in five division steps. The FINE POSI-TION controls, R488 (vertical) and R498 (horizontal) operate in a similar manner to the coarse controls except that the adjustment is continuously variable.

The POLARITY switch provides automatic positioning of the display when switching between the AC, +(NPN) or -(PNP) positions of the switch. This positioning current is obtained in the same manner as the coarse positioning current. Current sources R474 and R475 (vertical) and R477 and R478 (horizontal) provide this positioning current.

The display may also be positioned by the calibrated CENTERLINE VALUE switch This control affects the circuit only when the DISPLAY OFFSET Selector switch is switched to one of its VERT or HORIZ positions and affects only one display amplifier at a time When the DIS-PLAY OFFSET Selector switch is set to NORM (OFF) current sources B468 and B469 (vertical) and B471 and B472 (borizontal) supply current to the display amplifiers When for example, the switch is set to VERT, 8468 and R469 are disconnected from the circuit and an equal amount of current is supplied to the vertical display amplifier by current sources R450 through R464. These resistorcontact combinations are controlled by the CENTERLINE VALUE switch and operate identical to the POSITION switches. The CENTERLINE VALUE switch provides 10 divisions of calibrated positioning in half-division steps

Page 72

Display Switching

Once the desired voltages and currents have been sensed by the display sensitivity switching circuit, and once the desired positioning currents have been obtained from the display positioning circuit, the resulting voltage signals and positioning currents must be applied to the display amplifiers. Before being applied to the display amplifiers, however, these signals pass through the display switching circuit (see the Display Amplifiers and Display Positioning Switches schematics).

Under normal operating conditions with neither the DIS-PLAY INVERT, the ZERO nor the CAL buttons pressed, these signals and currents pass directly to the display amplifers. If the DISPLAY INVERT button is pressed, however, the signal and current (CENTERLINE VALUE Switch and POLARITY switch positioning current) input lines to both amplifiers are reversed. This causes the display on the CRT to be inverted, both vertically and horizontally.

The ZERO button, when pressed, disconnects the signal input lines from both pairs of high impedance inputs and shorts the input pairs together. This provides a zero reference for both display amplifiers. If the DISPLAY OFFSET controls are being used when the ZERO button is pressed, offset positioning current is caused to flow as if the CENTERLINE VALUE switch were set to 0 (see Display Positioning schematic and discussion of positioning).

The CAL button, when pressed, disconnects the signal input lines from both pairs of high impedance inputs and applies a substitute voltage across each input pair which should cause full graticule deflection (10 divisions by 10 divisions). This provides a means of checking the accuracy of calibration of the display amplifiers. The substitute voltage is determined by R501 through R513 and by D507. Since each display amplifier has three gains to check, three substitute voltages must be available. Relays K537C, K541C, K637C and K641C determine which voltages are applied to the high impedance input pairs for various settings of the VERTICAL and HORIZONTAL switches. If the DISPLAY OFFSET current controls are being used when the CAL button is pressed, offset current is caused to flow as if the CENTERLINE VALUE switch were set to 10.

Display Amplifiers

The vertical and horizontal display amplifiers are identical with a few minor exceptions. They are both differential amplifiers, each with two sets of differential inputs and one set of differential outputs. One set of differential inputs is high impedance and receives its inputs from the display sensitivity switching circuit. The other set of differential positioning currents from the display positioning circuit The differential outputs are connected to the deflection plates of the CRT and control the potential on the deflection plates.

The simplified schematic in Fig. 3-12 will help in under standing the operation of the display amplifiers. The display amplifiers is the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display amplifier of the display a

play amplifiers control the voltage between the deflection plates of the CRT by controlling the currents through load resistors R_L1 and R_L2. The currents I_L1 and I_L2 conducted by the load resistors are controlled by two means: differential current I_s and positioning currents Ip₁ and Ip₂. The differential current flows through source coupling resistor R_s whenever there is a differential voltage signal applied to the high impedance gate inputs of FETS Q1A and Q1B. Positioning currents Ip₁ and Ip₂ are determined by the resistance between the emitter of Q2A and -75 volts and between Q2B and -75 volts, respectively.

The relationship between the load resistor currents and the other currents in the amplifier is as follows:

$I_{I} = I_{P} - (I_{D} + I_{s})$ (Equation 3-1)

Equation 3-1 pertains to the currents which flow in one side of the amplifier. Is is either positive or negative, depending on whether it adds to or subtracts from ID. ID represents the FET drain current. It originates from a constant current source and is the same in each side of the amplifier. This equation also shows that the load current is dependent on the interaction between the differential current (Ip).

To understand the operation of this circuit, first assume that the amplifier is operating in a balanced condition where the two positioning currents are equal (Ip1 = Ip2) and there is no voltage difference between the two high impedance inputs (I_S = 0). In this case, the load currents or each side of the amplifier are equal to ILO. Equation 3-1 then becomes:

||0 = ||1 = ||2 = |P1 - |D = |P2 - |D (Equation 3-2)

To illustrate the effect the high impedance inputs have on the load current assume that a difference in voltage is applied across the gates of Q1A and Q1B, making the gate of Q1A more positive. This voltage differential causes dif ferential current le to flow through source coupling resist ance B. With this additional current (I.) flowing through 014 less current is needed from 024 to keep drain current Lo constant. The current conducted by Q2A is thus reduced to In - Is. Since the positioning current Ip1 which supplies the current conducted by O2A is also con stant there is a surplus of positioning current created equa to Is which must be conducted by 05 and therefore B11 The load current is increased to 1 1 = 1 0 + 1s. On the other side of the amplifier, the current through Q2B is increased to 1 + 1s, which decreases the load current through Q6 and R1 2 to I1 2 = I1 0 - Is. For this example it can be seen that whenever a differential voltage occurs between the two high impedance inputs the load currents change thus changing the voltage potential between the deflection plates of the CBT

To illustrate the effect the positioning currents have or the load currents assume that the voltages at the high

Page 73

impedance inputs are equal (I_S = 0) and that the positioning currents are unequal (I_P1 ≠ I_P2). From Equation 3-1 the load currents are found to be:

LI 1 = LP1 - LD (Equation 3-3)

12 = 12 - 10 (Equation 3-4)

By subtracting Equation 3-4 from Equation 3-3, it is shown that the difference in the two load currents exactly equal the difference in the two positioning currents.

$I_{L1} - I_{L2} = I_{P1} - I_{P2}$ (Equation 3-5)

Since the positioning currents are now unequal, the load currents (IL1 and IL2) are unequal, which again changes the voltage potential between the deflection plates of the CRT.

These two examples have shown that the voltage between the deflection plates (and thus the position of the electron beam as it strikes the face of the CRT) is controlled by two means, the voltage applied to the high impedance inputs and the positioning currents applied to

Page 74

the low impedance inputs. Equation 3-1 shows this relationship.

It should be noted that it is transistors Q3 and Q4 which cause Q5 and Q6 to conduct more or less load current. As in previous examples, assume the normally constant drain current I_D conducted by Q1A is caused to increase either by increasing I_s or I_P1. This increase in I_D causes the drain voltage of Q1A to go negative, causing Q3 to conduct more current. This in turn causes Q5 to conduct more current. The additional current conducted by Q5 reduces the current through Q2A and causes the drain current I_D to be reduced back to its normal constant value.

The gain of the display amplifiers is adjusted in two ways. The overall gain is controlled by varying the load resistance (R₁ and R₂). Adjusting the load resistance affects the gain of the high impedance inputs, as well as that of the positioning current. R₁ and R₂ are adjusted so that the positioning inputs provide the proper deflection. Varying the source coupling resistance (R_s) sets the gain of the high impedance inputs only. R_s is adjusted to match the high impedance gain to the positioning inputs.

By switching R_M into the circuit, the overall display amplifier gain is increased by a factor of 10. Load currents I_L1 and I_L2 flow through resistors R_N1 and R_N2. When R_M is in the circuit, any change in the current through R_N1 and R_N2 causes a voltage across R_M. This voltage across RM causes additional load current to be conducted by Q5 and Q6, load current which is not felt by the emitters of Q2A and Q2B. For a given change in current at the emitters of Q2A and Q2B, therefore, a greater change in load current through Q5 and Q6 occurs, causing additional gain of the display amplifier. The gain of the circuit under magnified conditions is controlled by adjusting R_M.

Vertical Display Amplifier

The Display Amplifiers schematic shows the complete schematic of the vertical display amplifier. The table in Fig. 3-12 relates the transistors and FETs in the simplified schematic with those in the actual schematic of this circuit.

The complete schematic shows that the high impedance inputs of the amplifier have three separate gains (B₀ has three different values) As has been mentioned previously in the discussion of the signal sensing and display sensitivity. the deflection factor of the vertical display is partially determined before the measurement is applied to the high impedance inputs. The three gains of the vertical display amplifier allow the vertical display to have three different deflection factors for each voltage signal applied to the high impedance inputs in a 1-2-5 relationship 1'S GAIN adjustment B541 2'S GAIN adjustment B538 and 5'S GAIN adjustment B536 determine the three gains of the high impedance inputs Relays K537A and K541A determine which resistors will control the gain for the various positions of the VERTICAL switch, VERT OUTPUT GAIN adjustment B592A and B determines the overall gain of the

vertical display amplifier by allowing adjustment of the load resistors R₁ and R₁ 2.

The overall balance of the positioning currents of the vertical display amplifier is controlled by VERT CENT adjustment R581. In addition, 1'S BAL adjustment R550 and 2'S BAL adjustment R545 provide positioning current balance when the VERTICAL switch is set to a position with a one times or a two times multiplier, respectively. Relays K537B and K541B determine which resistors control the positioning current balance for various positions of the VERTICAL switch.

When the DISPLAY OFFSET Selector switch is set to VERT X10, R574 and VERT MAG GAIN adjustment R573 are added to the vertical display amplifier circuit. These resistors constitute R_M and increase the sensitivity of the vertical display 10 times. R580 is always in the circuit and gives the output stage an unmagnified current gain of about 1.8.

Horizontal Display Amplifier

The Display Amplifiers schematic shows the complete schematic of the horizontal display amplifier. The table in Fig. 3-12 relates the transistors and FETs in the simplified schematic with those in the actual schematic of this circuit.

The horizontal display amplifier operates basically the same as the vertical display amplifier 1'S GAIN adjustment P629 2'S CAIN adjustment P636 and 5'S GAIN adjustment B641 control the three gains of the horizontal high impedance inputs Belays K637A and K641A determine which resistors will control the gain for the various positions of the HORIZONITAL switch HORIZ OUTPUT GAIN adjustment B692A and B controls the load resistance OBTHOG adjustment R685 interacts with the vertical display amplifier and allows adjustment of the orthocondition of the display on the CPT. When the DISPLAY OFESET Selector switch is set to HORIZ V10 R674 and HORIZ MAG GAIN adjustment R673 are added to the circuit and form BAA B680 like B580 is always in the circuit and round him him, hood, like hood, is always in the nain of about 1.8

The overall balance of the position currents of the horizontal display amplifier is controlled by HORIZ CENT adjustment R681. In addition, 1'S BAL adjustment R650 and 5'S BAL adjustment R645 provide positioning current balance when the HORIZONTAL switch is set to a position with a one times or a five times multiplier, respectively. Relays K637B and K641B determine which resistors control the positioning current balance for various positions of the HORIZONTAL switch.

READOUT

A display of the vertical and horizontal deflection factors, the step amplitude and the ß or g_m per division (vertical deflection factor divided by step amplitude) is given to the right of the CRT. This display of numbers and units is

Page 75

obtained through the use of fiber-optic readout. Fiber-optic readout involves the use of plastic fibers of very small June diameter, called light tubes, for transferring light from one place to another. The light tubes are designed so that the light incident at one end of the tube is transmitted through the tube to the other end. If the output end of the tube is viewed directly, the output light looks like a small dot. This transmission of light occurs even if the light tubes are bent at slight angles. In order to form a character, many light tubes are arranged so that their output ends, the dots of light, are in the configuration of the character to be formed. The input ends are then arranged so that they receive their incident light from the same light source. In some cases it may take two or more light sources to form one character. Whenever the proper light source (or sources) is illuminated, the desired character appears. It is the purpose of the readout circuitry, therefore, to light the readout lamps so the deflection factors they indicate correspond with the CRT display deflection factors determined by the positions of the VEBTICAL and HOBIZON-TAL switches, the MODE switch, the DISPLAY OFFSET Selector switch, the AMPLITUDE switch and the .1X STEP MULT button.

The inputs for the readout logic come from logic lines whose logic levels are controlled by the switches shown on the Readout Switching and Interconnections schematic, or by externally provided logic levels. The form of the inputs is a high-low code. Normally all inputs are high and the code is determined by switching some of the logic lines to ground. Ground reference is generally provided directly as part of the switch. However, in the case of the vertical and horizontal switches, ground is provided through saturated transistors Q900 and Q943 respectively. If lows are applied to pins 7 and 20 of J363, these transistors are turned off. In this case ground reference for the affected logic lines must then be provided externally.

The readout logic (see Readout Logic schematic) primarily consists of integrated circuit decoders. These decoders receive inputs from the incoming logic lines in terms of the above-mentioned switch code. This input code is then translated into a high-low lamp code which appears on the output logic lines. Each of the output logic lines is connected to a readout lamp (see Readout Lamps schematics) and each lamp illuminates one character or part of a character. A low on a readout lamp causes the lamp to light. The intensity of the readout is determined by the 0 to 4.5 volt supply.

The readout logic circuitry also generates a lamp code which produces a readout of beta or transconductance (g_m) per division. This β or g_m readout lamp code is obtained by dividing the vertical lamp code by the steps lamp code.

The decoders which control the horizontal deflection factor readout are U951 and U953. Inputs to these decoders are controlled by the HORIZONTAL switch, the DISPLAY OFFSET Selector switch or by externally

Circuit Description-Type 576

applied inputs to J363. Outputs from these decoders go to the horizontal readout lamps. As an example of how a lamp code is generated, assume that the HORIZONTAL switch is set to .5 V COLLECTOR and the DISPLAY OFFSET Selector switch is set to NORM (OFF). Due to the closing of contacts by the HORIZONTAL cam switch (see the Readout Switching and Interconnections schematic), lows are applied to the inputs to U951 and U953 at connectors 13, T, and S of P950 (see Fig. 3-13). The other inputs to the horizontal decoders are held high. The output lamp code resulting from this input code is lows at lamp input connectors F, I, J, L, A, C, D and E. The resulting PER HORIZ DIV readout is 500 mV, which corresponds with the .5 V COLLECTOR position of the HORIZONTAL switch.

Decoders U956 and U960 control the vertical deflection factor readout. Inputs to these decoders are controlled by the VERTICAL switch, the DISPLAY OFFSET Selector switch, the MODE switch and externally applied inputs to J363. Outputs from these decoders go to the vertical readout lamps. The horizontal and vertical decoders are also affected by the logic inputs, at pin U, pin Y and pin 12 of J950, whose logic levels may only be determined externally.

Decoders U965 and U970 control the step amplitude readout. Inputs to U965 and U970 are controlled by the AMPLITUDE switch, the STEP MULT .1X button and externally applied inputs to J361. Outputs from U965 and U970 go to the steps readout lamps.

The beta or g_m generator consists of U974, U975 and U976. The input code received by these decoders is a combination of logic levels coming in part from the vertical lamp code, and in part from the steps lamp code. The outputs from these decoders go to the beta readout lamps. Q960 and Q974 decode the logic levels appearing at pins 13 and 15 of U960 and pins 13 and 15 of U970. Q977 and Q979 provide a means of lighting the 1,4 lamp (connector BI) whenever the 2,5 lamp (connector AR) is off.

POWER SUPPLY

Low Voltage Power Supply

The Type 576 can be operated either from a 115-volt or a 230-volt line voltage source. The low voltage power supply (see Fig. 3-14) consists of a single transformer, T701, which has nine secondaries. This supply provides six regulated voltages: -75 volts, -12.5 volts, +5 volts, +12.5 volts, +15 volts and +100 volts. It also produces a regulated variable voltage of 0 to 4.5 volts, one unregulated voltage of +50 volts and an AC voltage to drive the POWER ON light and the GRATICULE ILLUM lights. In addition the windings providing a source of clock pulses for the step generator and the CRT heater are among the nine secondaries of T701. All the regulated power supplies are completely short proof.

Input Circuit. When the POWER switch is switched to ON, line current flows from the input, P701 (see Power Supply schematic), through power switch SW701, fuse F701, Thermal Cutout TK701 and into the primary wind-

Page 76

Fig. 3-13. Example of operation of Horizontal Readout decoders.

ings. For 115-volt operation the LINE SELECTOR switch connects the two primaries in parallel and for 230-volt operation connects them in series. For 230-volt operation, F703 is connected into the circuit. The RANGE SELEC-TOR plug determines how many turns of each primary winding are utilized to compensate for variations in line voltage.

-75-volt Supply. The -75-volt supply consists of diode bridge D706 A, B, C and D, filter capacitors C706 and C707, comparator Q716A and B, emitter follower Q729, short protection Q725 and Q727, and series regulator Q734.

9-volt Zener diode D708 sets the base voltage of comparator transistor Q716A while the quiescent voltage at the base of Q716B is set by -75 V adjustment R721. Any variation in the -75-volt supply voltage is compared by Q716A and B. The resulting rise or fall in voltage across R715 is transmitted by Q729 to the base of series regulator Q734. Any change in voltage of the -75-volt supply will be opposed by a change in current through the series regulator.

The output current of the -75 volt supply is limited to a value less than normal whenever the supply is shorted to a voltage between -75 V and chassis ground. The supply current of the -75 volt supply is controlled by the voltage across R735, which is dependent on the base voltage of Q734. This voltage is in turn dependent on the voltage across R730 and R731. As the -75 volt supply becomes more positive (due to shorting it to a more positive supply), the voltage at the base of Q734 is raised, causing more

supply current to be conducted through R735. As the supply voltage becomes more positive, the voltage at the junction of R730 and R731 rises high enough to turn on Q727. When Q727 turns on, it begins pulling down on the base voltage of Q729 and down on the base voltage of Q734, thus limiting the supply current. The output current of the -75-volt supply comes less, the closer the supply voltage is to ground.

D732 prevents the supply from going more than 0.6 volt above chassis ground if the -75 volt supply is shorted to a positive voltage. D722 protects the -12.5 volt supply if it is shorted to the -75 volt supply. If the -12.5 volt supply is pulled negative, D722 turns on when the supply is about at -15 volts which disables comparator Q716A and B. The -75 yolt supply then limits current until both supplies are at about -2.5 volts. If the +12.5 volt supply is shorted to the +100 volt supply, Q725 turns on. When Q725 is on, it limits current through R735 in the same manner as discussed previously for Q727. The result of shorting the +12.5 volt supply to a more positive voltage is to turn off the -75 volts supply. Since the -75 volt supply is the reference for the -12.5 volt. +12.5 volt. +100 volt. and CRT voltage supplies, when the -75 volt supply is turned off, the other power supplies are turned off.

-12.5-volt Supply. The -12.5 volt supply consists of diode bridge D737A, B, C and D, filter capacitor C738, comparator Q744A and B, emitter follower Q750, short protection Q748 and series regulator Q756. This circuit regulates the -12.5-volt supply in essentially the same manner as the -75-volt supply operates.

Page 77

Fig. 3-14. Block diagram of L. V. Power Supply.

Page 78

0 to +4.5-volt Variable Supply. The 0 to +4.5-volt variable supply consists of diode bridge D758A, B, C and D, filter capacitor C759, comparator Q767A and B, emitter follower Q774, short protection Q772 and series regulator Q778. This circuit operates in essentially the same manner as the -75-volt supply circuit. In this circuit, however, the reference voltage at the base of Q767A is variable from 0 volts to +4.5 volts by the READOUT ILLUM control, R760, and divider R762 and R763. The output current of the supply is limited by Q772.

+5-volt Supply. The +5-volt supply consists of error amplifier Q780, short protection Q784 and series regulator Q787. The supply shares diode bridge D758A, B, C and D and filter capacitors C758 and C759 with the +4.5-volt supply. Any variation in the +5-volt supply voltage is amplified by Q780, causing the base voltage of Q787 to vary in opposition to the variation of the supply. The current conducted through R788 by the supply is thus regulated, which in turn regulates the +5-volt supply. Q784 provides short protection by turning on whenever the current through R788 becomes excessive. When Q784 turns on, the base voltage of Q787 is pulled down, limiting the current through R788.

+12.5-volt Supply. The +12.5-volt supply consists of diode bridge D790A, B, C and D, filter capacitor C791, comparator Q795A and B, emitter follower Q803, short protection Q800, and series regulator Q808. This circuit operates in essentially the same manner as the -75-volt supply. Short protection of the +12.5-volt supply when it is shorted to a more positive voltage is provided by Q725 of the -75-volt supply. If the +12.5-volt supply voltage is pulled up, the base of Q725 is also pulled up, turning on Q725. With Q725 turned on, the base of Q729 is pulled down turning off the -75-volt supply.

+15-volt Supply, Camera Power. The +15-volt supply consists of error amplifier Q810, emitter follower Q817, short protection Q814 and series regulator Q819. The supply shares diode bridge D790 and filter capacitors C790 and C791 with the +12.5-volt supply. Any variation in the +15-volt supply voltage is amplified by Q810, causing an opposing variation in the voltage at the base of Q817. This opposing voltage variation is transmitted through the emitter of Q817 to the base of series regulator Q819 where it controls the current conducted by R819 and thus regulates the supply. When enough current is conducted by Q819 to turn on Q814, the voltage at the base of Q817 is pulled down thus limiting the current through Q819.

+50-volt Supply. The +50-volt supply consists of diode bridge D821A, B, C and D, and filter capacitors C822 and C823. It is a floating unregulated supply used to power the step amplifier output.

+100-volt Supply. The +100-volt supply consists of diode bridge D828A, B, C and D, filter capacitor C829,

error amplifier Q834, emitter follower Q840, short protection Q837 and series regulator Q846. Any variation in voltage by the +100-volt supply is amplified by Q834 and transmitted through Q840 to the base of Q846. Since any variation in the supply is inverted by Q834, the base voltage of Q846 will always move in opposition to a variation of the supply. The current conducted by R846, therefore, also is conducted so as to oppose any change in supply voltage. When enough current is conducted by Q846 to turn on Q837, the voltage at the base of Q840 is pulled down, thus limiting the current conducted by Q819.

CRT Voltage Power Supply

The CRT nower supply produces two high voltages -4 kV and +225 volts. for operation of the CRT and its related controls. In addition, the +225-volt supply is used by the display amplifiers. The source of power for the two supplies is a high frequency (about 28 kHz) Hartley oscillator which consists of 0851 and the two primaries of transformer T850. The collector of O851 is connected through the collactor primary R850 and 1850 to the +100-volt supply When current flows through the collector primary, a mag netic field is built up in the transformer core. Due to this field, a reverse base current is caused to be conducted through 0851 by the base primary and 0851 is eventually turned off With 0851 off no current flows through the collector primary. The residual field in the transformer core now causes forward base current to be conducted through 0851 turning it on As 0851 turns on current again flows through the collector primary, thus beginning a new cycle The frequency of the oscillator and thus the output current of the secondaries is controlled by the voltage on pin 2 of the base primary.

-4 kilovolt Supply. The -4 kV supply consists of halfwave rectifier D870, filter capacitors C870 and C871, and divider resistors R875 through R883. This supply is a halfwave rectified supply with D870 forward biasing on negative transistions of the voltage on the -4 kV secondary. The -4 kV supply voltage after being filtered by C870 and C871 is reduced by Zener diode D882 to provide the -3890 volt cathode voltage. The grid voltage is controlled by the divider made up of R882 and INTENSITY control R883. The voltage on the focus screen of the CRT is controlled by FOCUS control R880.

The -4 kV supply is regulated from a reference supply which is generated by the winding between terminals 6 and 5 of T850. This reference supply consists of half-wave rectifier D866 and D869, and filter capacitor C866. The regulator circuit consists of error amplifier Q859 and emitter follower Q855. Any variation in the reference supply voltage is transmitted to the base of Q859 through divider R860-R864. The variation is then amplified and inverted by Q859 and transmitted through Q855 to the base of Q851, where it regulates the drive of the oscillator. Any variation in current conducted by the -4 kV supply is conducted by R899, which causes the decoupled supply voltage at the emitter of Q859 to vary, thus compensating for current variation in the -4 kV supply

Page 79

The voltage on the display geometry screen is controlled by GEOMETRY adjustment R893. The voltage on the display astigmatism screen is controlled by ASTIGMATISM adjustment R891. Current for the trace rotation controlling coil is controlled by TRACE ROTATION adjustment R897.

ര

+225-volt Supply. The +225-volt supply is generated from the same transformer winding as the -4 kV reference supply. It consists of half-wave rectifier D868 and D865, filter capacitors C869, C868 and Q868. Regulation of the +225-volt supply is supplied by the reference supply through divider R860 through R864, and through emitter followers Q866 and Q868.

Page 80

NOTES

	-

	- 1











	_

Page 81

SECTION 4 MAINTENANCE

Introduction

This section of the manual provides information for use in preventive maintenance, troubleshooting and corrective maintenance of the Type 576.

PREVENTIVE MAINTENANCE

General

Preventive maintenance consists of cleaning, visual inspection, lubrication, etc. Preventive maintenance performed on a regular basis will improve the reliability of this instrument. The severity of the environment to which the Type 576 is subjected determines the frequency of maintenance.

Cleaning

The Type 576 should be cleaned as often as operating conditions require. Accumulation of dirt in the instrument can cause overheating and component breakdown. Dirt on components acts as an insulating blanket and prevents efficient heat dissipation. It can also provide an electrical conduction path.

Exterior. Loose dust accumulated on the outside of the Type 576 can be removed with a soft cloth or small paint brush. The paint brush is particularly useful for dislodging dirt on and around the front-panel controls. Dirt which remains can be removed with a soft cloth dampened in a mild detergent and water solution. Abrasive cleaners should not be used.

Interior. Dust in the interior of the instrument should be removed occasionally to prevent electrical conductivity under high-humidity conditions. The best way to clean the interior is to blow out the accumulated dust with dry, lowvelocity air. Remove any dirt which remains with a soft paint brush or a cloth dampened with a mild detergent and water solution. A cotton-tipped applicator is useful for cleaning in narrow spaces or for cleaning ceramic terminal strips and circuit boards.

CAUTION

Avoid the use of chemical cleaning agents which might damage the plastics used in this instrument. Avoid chemicals which contain benzene, toluene, xylene, acetone or similar solvents.

Lubrication

The reliability of potentiometers, rotary switches, and other moving parts can be maintained if they are kept prop-

erly lubricated. Use a cleaning-type lubricant on switch contacts. Lubricate switch detents with a heavier grease (such as Tektronix Part No. 006-0219-00). Shaft bushings and potentiometers that are not sealed should be lubricated with a lubricant which will not affect electrical characteristics (such as Tektronix Part No. 006-2574-00). Do not use excessive lubrication. A lubrication kit containing the necessary lubricants and instructions is available from Tektronix, Inc. (order Tektronix Part No. 003-0342-02).

Visual Inspection

The Type 576 should be inspected occasionally for such defects as broken connections, loose pin connections, broken or damaged ceramic strips, improperly seated transistors, damaged circuit boards and heat damaged parts.

The corrective procedure for most visible defects is obvious; however, particular care must be taken if heatdamaged components are found. Overheating usually indicates other trouble in the instrument; therefore, it is important that the cause of overheating be corrected to prevent recurrence of the damage.

Transistors and Integrated Circuits

Periodic checks of individual transistors and integrated circuits are not recommended. The best check of them is their operation in the equipment, as reflected by a performance check or calibration procedure. Sub-standard performance will normally be detected at that time.

Recalibration

To ensure accurate measurements, check the calibration of this instrument after each 1000 hours of operation or, if used infrequently, every 6 months. In addition, replacement of components may necessitate recalibration of the affected circuits. Complete calibration instructions are given in the Performance Check and Calibration section. This procedure may also be helpful in localizing certain troubles in the instrument. In some cases, minor troubles may be revealed and/or corrected by recalibration.

TROUBLESHOOTING

Troubleshooting Aids

Diagrams. A complete set of diagrams is given on foldout pages in Section 8, Diagrams. Each component in this instrument is shown on the appropriate diagram, along with its circuit number and electrical value. Also included on the circuit

Page 82

Maintenance-Type 576

circuit diagrams are voltages and waveforms which can be expected at various points in the circuitry. A block diagram and other information concerning the major circuits in the instrument are included at the beginning of the diagram foldouts.

Electrical Parts List. The electrical parts list contains a complete list of all the electrical components within the instrument in the order of their circuit numbers. A component description is also included for each part which provides: The Tektronix part number and electrical value (or substitute part number); and tolerance. Instructions for ordering replacement parts is provided at the beginning of the Electrical Parts List section.

Calibration Procedure. The Performance Check/Calibration section also provides an adjustment procedure which covers all the internal adjustments in the instrument. See the Performance Check/Calibration Record and Index in Table 5-2 for a list of the internal adjustments. The Performance Check/Calibration section provides a performance check procedure which will help determine whether a malfunction is due to improper calibration or to a circuit or component malfunction.

Circuit Description. A circuit description of each circuit in the instrument with accompanying block diagrams is provided in the Circuit Description section. This section is helpful when the source of a malfunction cannot be determined from the diagrams or the performance check/calibration procedure. Also included is a block diagram description that gives the theory of operation of the instrument.

Circuit Boards. Fig. 4-6 through Fig. 4-28, at the rear of this section, show all the circuit boards in the Type 576. The electrical components on each of these pictures are identified by their circuit numbers.

Wiring Color Code. All insulated wire and cable used in the Type 576 is color-coded to facilitate circuit tracing. Signal carrying leads have white backgrounds with one or two colored stripes. The signal carrying wire color-codes are given in Fig. 4-6 through 4-28 with the appropriate pin connection. Power supply leads have either a red background (positive supply) or a purple background (negative supply). Each power supply lead also has one colored stripe which represents its ordinal relationship to the other supplies having the same polarity, using the EIA resistor color code. Table 4-1 gives the wiring color-code for the power supply voltages used in the Type 576.

Power Cord Conductor Identification

Conductor	Color	Alternate Color
Ungrounded (Line)	Brown	Black
Grounded (Neutral)	Blue	White
Grounding (Earthing)	Green-Yellow	Green-Yellow

TABLE 4-1

Power Supply Wiring Color

Suppl y	Background Color	Stripe Color
—75 volt	Purple	Red
-12.5 volt	Purple	Black
Var +4.5 volt	Brown	(none)
+5 volt	Red	Black
+12.5 volt	Red	Brown
+50 volt	Red	Yellow
+15 volt	Red	Orange
+100 volt	Red	Green
+225 volt	Red	Blue
-4 kV	White	Purple
Ground	Black	(none)

Switch Wafer Identification. Switch wafers shown on the diagrams are coded to indicate the position of each wafer in the complete switch assembly. The numbered portion of the code refers to the wafer number counting from the front, or mounting end of the switch, toward the rear. The letters F and R indicate whether the front or rear of the wafer performs the particular switching function. For example, a wafer designated by 2R indicates that the rear of the second wafer (from the front) is used for this particular switching function.

Resistor Color Code. In addition to the brown composition resistors, some metal-film resistors (identifiable by their gray body color) and some wire-wound resistors (usually light blue or dark gray) are used in the Type 576. The resistance value of a wire-wound resistor is printed on the body of the component. The resistance value of a composition resistor or metal-film resistor is color-coded on the component with EIA color-code (some metal-film resistors may have the value printed on the body). The color-code is read starting with the stripe nearest the end of the resistor. Composition resistors have four stripes which consist of two significant figures, a multiplier and a tolerance value (see Fig. 4-1). Metal-film resistors have five stripes consisting of three significant figures, a multiplier and a tolerance value.

Capacitor Marking. The capacitance value of a common disc capacitor or small electrolytic is marked in microfarads on the side of the component body. The white ceramic capacitors used in the Type 576 are color-coded in picofarads using a modified EIA code (see Fig. 4-1).

Diode Color Code. The cathode end of each glass encased diode is indicated by a stripe, a series of stripes or a dot. For most silicon or germanium diodes with a series of stripes, the color-code identifies the Tektronix Part Number using the resistor color-code system (e.g., a diode colorcoded blue or pink-brown-grey-green indicates Tektronix Part Number 152-0185-00). The cathode and anode ends of

Page 83

Fig. 4-1. Color-code for resistors and ceramic capacitors.

inetal-encased diodes can be identified by the diode symbol marked on the body.

Transistor and Integrated Circuit Lead Configuration. Fig. 4-2 shows the lead configurations of the transistors and integrated circuits used in this instrument. The view is as seen from the bottom of the device

Troubleshooting Equipment

The following equipment is useful for troubleshooting the Type 576:

1. Semiconductor Tester-Some means of testing the transistors, diodes and FET's used in this instrument is helpful. A transistor-curve tracer such as the Tektronix Type 576 or 575 will give the most complete information.

2. DC Voltmeter and Ohmmeter—A voltmeter for checking voltages within the circuit and an ohmmeter for checking resistors and diodes are required. For most applications a 20,000 ohm/volt VOM can be used to check voltages and resistances, if allowances are made for the circuit loading of a VOM when making voltage measurements at high-impedance points.

3. Test Oscilloscope—A test oscilloscope is required to view waveforms at different points in the circuit. An oscilloscope with DC to 10 MHz frequency response and 10

mV to 10 V/division vertical deflection factor is suggested. A 10X probe should be used to reduce circuit loading.

Troubleshooting Techniques

CAUTION

High voltage may appear in many areas of this instrument. Read the entire maintenance section before removing the cabinet covers.

This troubleshooting procedure is arranged in an order which checks the simple trouble possibilities before proceeding with extensive troubleshooting. The first few checks ensure proper connection, operation and calibration. If the trouble is not located by these checks, the remaining steps aid in locating the defective component. When the defective component is located, it should be replaced following the replacement procedure given under Corrective Maintenance

1. Check Control Settings. Incorrect control settings can indicate a trouble that does not exist. If there is any question about the correct function or operation of any control, see the Operating Instructions section of this manual.

Page 84

Maintenance–Type 576

Fig. 4-2. Electrode configurations for socket-mounted semiconductor devices.

Page 85

2. Check Instrument Calibration. Check the calibration of this instrument or of the affected circuit if the trouble is known to exist in one particular circuit. The apparent trouble may be only a result of misadjustment and may be corrected by calibration. Complete calibration instructions are given in the Performance Check/Calibration section of this manual.

3. Locating Malfunctioning Circuits. To locate the source of a malfunction in instrument operation, the trouble symptom will often indicate the identity of the faulty circuit(s). For example, if a display of the Collector Supply output can be obtained on the test oscilloscope CRT but a display of the Step Generator output cannot be obtained, the Step Generator is probably malfunctioning.

If the trouble symptom does not indicate which circuit(s) is causing problems (for example, if there were no Collector Supply or Step Generator outputs), a more systematic troubleshooting procedure is necessary. Fig. 4-3 provides a general guide for locating the circuits which are most likely causing the instrument to malfunction

The following preliminary procedure ensures that the instrument malfunction is not caused by improper control settings and helps determine where to begin on the trouble-shooting chart:

A. Set the following Type 576 controls to:

GRATICULE ILLUM	Fully Clockwise
READOUT ILLUM	Fully Clockwise
INTENSITY	Trace Visible
FOCUS	Centered
VERTICAL	STEP GEN
DISPLAY OFFSET Selector	NORM(OFF)
CENTERLINE VALUE	0
HORIZONTAL	2 V COLLECTOR
POSITION (Vert and Horiz)	Centered
FINE POSITION (Vert and Horiz)	Centered
ZERO	Released
CAL	Released
DISPLAY INVERT	Released
MAX PEAK VOLTS	15
PEAK POWER WATTS	0.5
VARIABLE COLLECTOR SUPPLY	Fully Clockwise
POLARITY	+(NPN)
MODE	NORM
LOOPING COMPENSATION	As Is
NUMBER OF STEPS	10
CURRENT LIMIT	20 mA
AMPLITUDE	2 V
OFFSET	ZERO
OFFSET MULT	0
STEPS	Pressed
PULSED STEPS	Released
STEP FAMILY	REP
RATE	NORM
POLARITY INVERT	Released
STEP MULT .1X	Released

Terminal Selector	BASE TERM STE
	GEN
LEET-OEE-BIGHT	BIGHT

B. Turn on the Type 576 and allow a few minutes to warm up.

C. CHECK FOR—Display of the Collector Supply sweep of about 15 volts peak horizontally on the Type 576 CRT graticule and of the Step Generator signal of one step per division vertically.

D. If no display can be obtained or the display is incorrect, connect the 10X probe between the test oscilloscope and the collector terminal on the right hand side of the Standard Test Fixture (connect ground lead to emitter terminal).

E. CHECK FOR—Display of Collector Supply output a positive-going full-wave rectified sine wave of about 15 volts peak on test oscilloscope CRT.

F. Connect the probe to the right base terminal of the Standard Test Fixture.

G. CHECK FOR-Display of Step Generator output of positive-going steps of 2 volts/step on test oscilloscope CRT.

H. Start with the following step on Fig. 4-3 according to the results of the previous checks:

1. Step (A)—No Collector Supply output; Step Generator output or display on the Type 576 CRT.

2. Step (B)—No Collector Supply output or incorrect output, but Step Generator is displayed on the Type 576 CBT.

3. Step (C)—No Step Generator output (or incorrect output), but Collector Supply is displayed on the Type 576 CRT.

4. Step (D)–No display on type 576 CRT (or incorrect display), but Collector Supply output and Step Generator output are displayed properly on the test oscilloscope CRT.

After the defective circuit has been located using Fig. 4-3, proceed with steps 4 through 9 to locate and repair the faulty components.

4. Visual Check. Visually check the portion of the instrument in which the trouble is located. Many troubles can be located by visual indications such as unsoldered connections, broken wires, damaged circuit boards, damaged components, etc.

5. Check Circuit Board Interconnections. After the trouble has been isolated to a particular circuit, check the pin connectors on the circuit board for correct connection. Figs. 4-6 through 4-28 show the correct connections for each board.

The pin connectors used in this instrument also provide a convenient means of circuit isolation. For example, if the

Page 86

Maintenance-Type 576

Fig. 4-3. Troubleshooting chart

Page 87

power supply is shorted, the defective circuit can be isolated by disconnecting the pin connectors at the boards until the shorting condition is removed.

6. Check Voltages and Waveforms. Often the defective component can be located by checking for the correct voltages and waveforms as given on the circuit diagrams on foldout pages in the back of this manual.

NOTE

Voltages and waveforms given on the diagrams are not absolute and may vary slightly between instruments. To obtain operating conditions similar to those used to take these readings, see the beginning of the Diagrams section.

7. Check Semiconductors. Most circuit failures result from the failure of a transistor, FET, diode, or integrated circuit due to normal aging and use. The following explains various methods of checking semiconductor devices. Insertion information is provided in Fig. 4-2.

TRANSISTORS. Transistor defects usually take the form of the transistor opening, shorting, or developing excessive leakage. The best method of checking transistors is by direct substitution. Be sure the voltage conditions of the circuit are not such that a replacement transistor might also be damaged. If substitute transistors are not available, use a dynamic tester (such as a Tektronix Type 576).

Static-type testers are not recommended since they do not check the device under operating conditions. However, if no other tester is immediately available, an ohmmeter will usually indicate when a transistor is totally bad. As a general rule, use the R X 1 k range where the current is usually limited to less than 2 mA and the internal voltage is usually 1 1/2 volts. Check the current and voltage of the

TABLE 4-2 Transistor and FET Resistance Checks

Ohmmeter Connections	Resistance Readings That Can Be Expected Using the R X 1 k Range
Emitter-Collector	High readings both ways (about 60 kΩ to around 500 kΩ).
Emitter-Base	High reading one way (about 200 kΩ or more). Low reading the other way (about 400 Ω to 2.5 kΩ
Base-Collector	High reading one way (about 500 kΩ or more). Low reading the other way (about 400 Ω to 2.5 kΩ).
Drain-to-Source	Less than 500 Ω
Gate-to-Source and Gate-to-Drain	400 Ω to 10 Ω (approximately) in one direction; more than 200 kΩ with leads reversed.

ohmmeter by inserting a multimeter between the ohmmeter leads and measuring the current and voltage of the various ranges. After it has been determined which ohmmeter ranges will not harm the transistor, use those ranges to measure the transistor's resistance. Check the resistance in both directions through the junctions as listed in Table 4-3.

FIELD EFFECT TRANSISTORS. The voltage and resistance of field effect transistors can be checked in the same manner as transistors, 1 1/2 V and less than 2 mA should be used for ohmmeter checks. See Table 4-2 for proper resistance readings.

INTEGRATED CIRCUITS. Integrated circuits are best checked in the circuit with a voltmeter, test oscilloscope, or by direct substitution. A good understanding of the circuit description is essential when troubleshooting a circuit using integrated circuits. In addition, operating voltages and waveforms, logic levels and other operating information for the integrated circuits, which are provided in the Diagrams section, are also helpful, Use care when checking voltages and waveforms around the integrated circuits so that adjacent leads are not shorted together. A convenient means of clipping a test probe to the 14- and 16-pin integrated circuits is with an integrated-circuit test clip. This device also doubles as an integrated-circuit extraction tool.

DIODES. Diodes (except for tunnel diodes) can be checked for an open or short-circuited condition by measuring the resistance between the terminals after unsoldering one end of the component. Use a resistance scale with an internal voltage between 800 mV and 3 volts. The resistance should measure very high (in megohm range) in one direction and low in the other.

8. Circuit Description. If the malfunction has not been located after checking the voltages, waveforms and semiconductors, the circuit description should be consulted. The circuit description describes the purpose of the circuit and its components with emphasis on the semiconductors. It will help in determining voltages and waveforms not shown in the diagrams and thus help in further pin-pointing the source of the malfunction.

9. Check Other Components. If the semiconductors in the circuit have been found to be good, the rest of the components should be checked. Components which are soldered in place are best checked by disconnecting one end. This isolates the measurement from the effects of surrounding circuitry.

10. Repair and Readjust the Circuit. If any defective parts are located, follow the replacement procedures given in this section. Be sure to check the performance of any circuit that has been repaired or that has had any electrical components replaced. If a component has been replaced, recalibration is usually necessary.

Page 88

TABLE 4-3

Input and Output Lines to Horizontal Decoders U951 and U953

Inpu	uts	Outputs
Pins on J950	Title	Solder Point on Readout Logic Circuit Board	Title (Lamp)
14	2X	F	1, 2, 4, A, V
13	5X	G	1
12	AMPS	Н	2
15	OFF		2,5
17	.1X	L	5
16	10 2	Ĺ	V
Т	101	К	А
S	NEG EXP	A	m , n
		В	μ
		С	m
		D	02
		E	01

TABLE 4-4

Input and Output Lines to Vertical Decoders U956 and U960

Inp	uts	Outputs
Pins on J950	Title	Solder Point on Readout Logic Circuit Board	Title (Lamp)
19	2X	V	1, 2, 5, A, V
18	5X	W	1
U	Volts	Х	2
V	OFF	Y	2,5
W	.1X	Z	5
Y	10X	AA	V
20	10-1	AB	А
21	10-2	U	01
2.2	10-4	Т	0 2
Х	10-3	S	m
		R	μ
		Ő	m, n

Additional Troubleshooting Information

Troubleshooting the Readout. Malfunction of the readout display can be caused by three things: a burned out readout lamp, improper operation of the readout logic or improper operation of a cam switch. The best method of locating the malfunction is by checking the inputs and the outputs of the decoders for various positions of the front panel switches. Tables 4-3 through 4-6 show to which decoders the pins on the J950 are inputs. The state of these

TABLE 4-5

Input and Output Lines to Steps Decoders U965 and U970

Inp	uts	Outputs
Pins on J950	Titles	Solder Point on Readout Logic Circuit Board	Title (Lamp)
F	2X	AH	1,2,5,A,V
5	5X	AI	1
4	VOLTS	AJ	2
Н	OFF	AK	2,5
J	.1X	AL	5
K	10X	AM	V
8	10 ^-1	AN	A
9	10 ^-2	AG	01
10	10-4	AF	0 2
6	10 ^-8	AE	М
		AD	μ
	ļ	AC	m ,n

TABLE 4-6

Input and Output Lines To Beta Decoders U974, U975 and U976

Input	s	Outpu	ts
Solder Points on Readout Logic Circuit Board	lder Points on Titles adout Logic (Lamps) rcuit Board		Titles (Lamps)
R	μ (vert)	AW	к
S	m (vert)	AX	K,M
Collector Q960)	n (vert)	AY	m
AE	m (steps)	AZ	К,μ
Collector Q974	n (steps)	BA	μ
AD	μ (steps)	BD	5 ₂
AG	0 ₁ (steps)	BE	DEC PT
AF	0 ₂ (steps)	BF	0,52
U	0 ₁ (vert)	BG	01
T	0 ₂ (vert)	BH	02
X	2 (vert)	AQ	4,5
Z	5 (vert)	AV	1,2,4
AL	5 (steps)	AS	2
AJ	2,5 (steps)	AT	2,4,5
Collector Q984	BETA OFF	AV	1,4,5
		AR	2,5
		BI	1/

pins (high or low) for various front-panel control settings can be obtained from the Readout Switching and Interconnections schematic in the Diagrams section. The outputs of the decoders are checked by first determining what the readout ought to be for the given settings of the front-panel

Page 89

TABLE 4-7

Supply Voltages When One Supply is Shorted to Ground

Shorted				Supply Vol	tages (Appr	oximate)
Supply	-75	-12.5	+12.5	+100	+225	-4 kV	+4.5	+5	+15
-75	0	0	1	3	0	0	0	0.5	1
-12.5	-35	0	1.5	3	0	0	1	1	1
+12.5	-75	0	0	+100	0	0	0	0	1.5
+100	-75	-1	1.5	0	0	0	0	0	0
+225	75	-12.5	5	8	0	0	2	3	6
4 kV	75	-12.5	5	8	0	0	2	3	6
4.5	-75	-12.5	+12.5	+100	+225	-4 kV	0	+5	+15
+5	-75	12.5	+12.5	+100	+225	4 kV	+4.5	0	+15
+15	75	-12.5	+12.5	+100	+225	4 kV	+4.5	+5	0

controls (be sure to note the effects of the MODE switch, DISPLAY OFFSET Selector switch and STEP MULT .1X button). When the proper readout has been determined, locate the pins on the Readout Logic circuit board which must be low to cause that readout (see Tables 4-3 through 4-6). When the proper states of the inputs and outputs of the decoders have been determined, check these levels with a voltmeter. A Type 576 READOUT EXTENDER (Tektronix Part No. 067-0603-00) is available to aid in troubleshooting the readout.

1. If the inputs to the decoders are incorrect, something is wrong with one of the cam switches.

2. If the inputs to the decoders are correct, but the outputs are incorrect, the decoders are malfunctioning.

Resistance Check ¹
Supply	VOM Scale	Resistance
		Leads +	Leads –
7 5	1 kΩ	1.5 k	1.9 k
+100	1 kΩ	5 k	1.8 k
+15	1 kΩ	23 k	_ 2 k
+225	1 kΩ	36 k	12 k
-12.5	10 Ω	25 Ω	35 Ω
+12.5	10 Ω	16 Ω	31 Ω
+5	10 Ω	28 Ω	90 Ω
+4.5 ²	10 Ω	35 Ω	100 Ω

TABLE 4-8 Power Supply

¹Type 576 turned off.

²READOUT ILLUM control fully clockwise.

3. If the outputs of the decoders are correct, something is wrong with a fiber-optic and lamp assembly (probably a burned out lamp).

See the section of the Circuit Description on readout for further information and an example of the operation of the readout system.

Power Supply. A malfunction in the power supply is often caused by one or more supplies being shorted to ground. Table 4-7 indicates the states of all the power supplies in the instrument when one of them is shorted to ground. This table does not give values in cases when more than one supply is shorted to ground or when one supply is shorted to another supply. In these cases, the table only indicates interrelationships between supplies. Table 4-8 gives resistance values of the supplies to ground as measured by a VOM. Be sure the instrument is turned off when making these measurements.

CORRECTIVE MAINTENANCE

General

Corrective maintenance consists of component replacement and instrument repair. Special techniques required to replace components in this instrument are given here.

Obtaining Replacement Parts

Standard Parts. All electrical and mechanical part replacements for the Type 576 can be obtained through your local Tektronix Field Office or representative. However, many of the standard electronic components can be obtained locally in less time than is required to order them from Tektronix, Inc. Before purchasing or ordering replacement parts, check the parts list for value, tolerance, rating and description.

NOTE

When selecting replacement parts, it is important to remember that the physical size and shape of a component may affect its performance, particularly at the upper frequency limits of the instrument. All replacement parts should be direct replacements unless it is known that a different component will not adversely affect instrument performance.

Special Parts. In addition to the standard electronic components, some special parts are used in the Type 576. These parts are manufactured or selected by Tektronix, Inc. to meet specific performance requirements, or are manufac-

Page 90

Maintenance-Type 576

tured for Tektronix, Inc. in accordance with our specifications. Each special part is indicated in the electrical parts list by an asterisk preceding the part number. Most of the mechanical parts used in this instrument have been manufactured by Tektronix, Inc. Order all special parts directly from your local Tektronix Field Office or representative.

Ordering Parts. When ordering replacement parts from Tektronix, Inc., include the following information.

1. Instrument Type.

2. Instrument Serial Number.

3. A description of the part (if electrical, include circuit number).

4. Tektronix Part Number.

Soldering Techniques

WARNING

Disconnect the instrument from the power source before soldering.

Circuit Boards. Use ordinary 60/40 solder and a 35- to 40-watt pencil type soldering iron on the circuit boards. The tip of the iron should be clean and properly tinned for best heat transfer to the solder joint. A higher wattage soldering iron may separate the wiring from the base material

The following techniques should be used to replace a component on a circuit board. Most components can be replaced without removing the boards from the instrument.

1. Grip the component lead with long-nose pliers. Touch the soldering iron to the lead at the solder connection. Do not lay the iron directly on the board, as it may damage the board.

2. When the solder begins to melt, pull the lead out gently. This should leave a clean hole in the board. If not, the hole can be cleaned by reheating the solder and placing a sharp object such as a toothpick into the hole to clean it out. A vacuum-type desoldering tool can also be used for this purpose.

3. Bend the leads of the new component to fit the holes in the board. If the component is replaced while the board is mounted in the instrument, cut the leads so they will just protrude through the board. Insert the leads into the holes in the board so the component is firmly seated against the board (or as positioned originally). If it does not seat properly, heat the solder and gently press the component into place

4. Touch the iron to the connection and apply a small amount of solder to make a firm solder joint. To protect heat-sensitive components, hold the lead between the component body and the solder joint with a pair of long-nose pliers or other heat sink

5. Clip off the excess lead that protrudes through the board (if not clipped in step. 3)

6. Clean the area around the solder connection with a flux-remover solvent. Be careful not to remove information printed on the board.

Ceramic Terminal Strips. Solder used on the ceramic terminal strips should contain about 3% silver. Use a 40- to 75-watt soldering iron with a 1/8-inch wide wedge-shaped tip. Ordinary solder can be used occasionally without damage to the ceramic terminal strips. However, if ordinary solder is used repeatedly or if excessive heat is applied, the solder-to-ceramic bond may be broken.

A sample roll of solder containing about 3% silver is mounted on the right side of the instrument below the bracket holding the VERT OUTPUT GAIN and HORIZ OUTPUT GAIN adjustments. Additional solder of the same type should be available locally, or it can be purchased from Tektronix, Inc. in one-pound rolls order by Tektronix Part No. 251-0514-00.

Observe the following precautions when soldering to a ceramic terminal strip:

1. Use a hot iron for a short time. Apply only enough heat to make the solder flow freely.

2. Maintain a clean, properly tinned tip

3. Avoid putting pressure on the ceramic terminal strip

4. Do not attempt to fill the terminal-strip notch with solder; use only enough solder to cover the wires adequate-

5. Clean the flux from the terminal strip with a flux remover solvent.

Metal Terminals. When soldering to metal termianls (e.g., switch terminals, potentiometers, etc.), ordinary 60/40 solder can be used. Use a soldering iron with a 40- to 75-watt rating and a 1/8-inch wide wedge-shaped tip.

Observe the following precautions when soldering to a metal terminal:

1. Apply only enough heat to make the solder flow freely

2. Apply only enough solder to form a solid connection. Excess solder may impair the function of the part.

3. If a wire extends beyond the solder joint, clip off the excess.

4. Clean the flux from the solder joint with a fluxremover solvent

Component Removal and Replacement

WARNING

Disconnect the instrument from the power source before replacing components.

Not all the components in this instrument are accessible without first removing some obstructions, such as circuit boards, CRT and shield or the guard box. None of these obstructions, however, are difficult to remove or replace.

Page 91

CRT and Shield. To adjust the CRT, to remove the CRT, or to remove the CRT and shield, follow these procedures:

Removal of CRT

1. Remove the bezel from the Type 576 front panel.

2. Remove the power cord retainer from the rear panel.

3. Disconnect the connector on the rear of the CRT by pulling on the white handle.

4. Loosen the CRT clamp from the neck of the CRT by loosening the Allen head screw (from the rear) on the right side of the clamp.

5. Disconnect the pin connectors from the side of the CRT.

6. Push the CRT from the rear, while pulling it from the front.

Removal of CRT Shield

1. Remove the CRT.

2. Disconnect the shield from the rear by loosening the clamps which secure the shield to the rear panel.

3. Disconnect the red and white wires from the READ-OUT INTERCONN circuit board. Disconnect the pin connectors from the graticule light circuit board.

4. Remove the readout.

5. Remove the screw which connects the readout illumination light circuit board to the chassis.

6. Remove the screw which is under the center frame section (the section the handle is connected to) on the instrument's right, in front

7. Remove the four screws securing the shield to the front panel.

8. Pull the shield out from the front of the instrument.

To replace the CRT and shield reverse these procedures. Use the following procedure to adjust the CRT once it has been replaced.

Adjustment of CRT

1. With the bezel in place on the Type 576 front-panel, note in which direction the CRT is out of alignment (all graticule lines should be visible).

2. Remove the bezel.

3. Loosen the four hexagonal head screws which secure the CRT support blocks. (Screws are located about 3 inches back from the front of the CRT shield.)

4. Loosen the CRT and pull it forward until the CRT support blocks are accessible.

5. Push the upper CRT support blocks back as far as possible.

6. Adjust the lower CRT support blocks so that the CRT will be properly aligned when put back in place.

7. Replace the CRT (do not secure).

8. Replace the bezel (do not secure).

9. Check that the CRT is now properly aligned

10. If the CRT is still not properly aligned, remove the bezel and CRT and readjust the bottom CRT support blocks.

11. Repeat steps 7 through 10 until the CRT is properly aligned.

12. Tighten the hexagonal head screws which secure the bottom CRT support blocks.

13. Push the upper CRT support blocks forward (by pushing on the hexagonal head screws) until they are firmly against the CRT and tighten the upper hexagonal head screws.

14. Secure the CRT.

15. Remove the bezel.

16. Check that the graticule lamp reflector fits tightly against the top of the CRT.

17. If the reflector is not properly aligned, realign it.

18. Replace and secure the bezel.

Guard Box.

WARNING

Power switch must be turned off before removing or replacing the phenolic shield on the guard box. Lethal voltages may appear on the components in the guard box and on the metal portions of the guard box.

Guard Box. The suggested method of gaining access to components located in the guard box is to remove the CRT and shield or remove the bottom panel of the instrument. All components in the guard box except for D310 can then

Fig. 4-4. MAX PEAK VOLTS- PEAK POWER WATTS switch assembly.

Page 92

Maintenance-Type 576

be removed either by removing the guard box cover or through the bottom of the instrument. If for some reason it is necessary to remove the guard box, use the following procedure:

1. Remove the right side panel from the Type 576.

2. Disconnect the MAX PEAK VOLTS—MAX PEAK POWER WATTS switch assembly as follows:

a. Set the MAX PEAK VOLTS indicator to 15 and the SERIES RESISTORS indicator to .3.

b. Looking behind the front panel, loosen the Allen screw which can be seen through the hole in the front of the front coupler half (see Fig. 4-4).

c. Set the SERIES RESISTORS indicator to 650 and loosen another Allen screw which now appears through the hole in the coupler half.

d. Pull the top portion of the switch assembly out through the front panel.

e. Loosen the two Allen screws in the spacer sleeve

f. Loosen the Allen screw in the end of the front coupler half.

g. Pull the bottom portion of the switch assembly through the front panel.

3. Disconnect the LOOPING COMPENSATION shaft from the coupler to the guard box by loosening the two Allen screws in the coupler.

4. Disconnect P300 from the guard box.

5. Turn the Type 576 on its side and remove its bottom cover.

6. Remove the screws from the chassis which hold the quard box in place.

7. Carefully pull the guard box out of the instrument (it is very heavy). The MODE switch coupling should disconnect as the guard box is removed.

To replace the guard box, reverse the preceding procedure.

Circuit Board Replacement. Most of the components mounted on the circuit boards can be replaced without removing the boards from the instrument. Observe the soldering precautions given under Soldering Techniques in this section. If a circuit board is damaged beyond repair, either the entire assembly (including all soldered-oncomponents) or the board only can be replaced. Part numbers are given in the Mechanical Parts List for either the completely wired board assembly or the unwired board.

Use the following procedure to remove a circuit board.

1a. To lift the board for maintenance or access to areas beneath the board, disconnect the pin connectors which might impair lifting.

1b. To completely remove the board disconnect all the remaining pin connectors.

2. Remove all screws holding the board to the chassis.

3. Lift the circuit board partially or all the way out of the instrument. Do not force or bend the board.

4. To replace the board, reverse the order of removal. The correct connections of the pin connectors is shown in Figs. 4-6 through 4-28. Reconnect the pin connectors carefully so they mate correctly with the pins. If forced into place incorrectly, the pin connectors may be damaged.

Cam Switches. A complete cam switch is actually a cam switch assembly. Each assembly consists of a nylon cam which is rotated by a front panel knob, and a set of contacts mounted on an adjacent circuit board which are actuated by the lobes on the cam. A cam switch repair kit including the proper repair tools, instructions and replacement contacts is available from Tektronix, Inc. (Tektronix Part No. 040-0541-00).

CAUTION

Repair of cam switches should be undertaken only by experienced maintenance personnel. The switch alignment and spring tension of the contacts must be carefully maintained for proper operation of the switch. For assistance in the maintenance of cam switches, contact your local Tektronix Field Office or representative.

Removal of a Cam Switch Assembly.

1a. To remove the cam switch assembly for maintenance or access to areas beneath, disconnect only those pin connectors which might impair lifting.

1b. To completely remove the assembly disconnect all the pin connectors.

2. Disconnect the switch from the front panel

3. Disconnect the circuit board from the rear mounting bracket.

NOTE

The thin film resistors on some of the cam switch assemblies are brittle. Do not bend them when handling.

4. Remove the switch assembly from the instrument.

Page 93

Maintenance–Type 576

NOTE

The rear mounting bracket will bend outward allowing enough clearance to remove assembly.

Disassembling the Cam Switch Assembly.

1. Remove the cam switch assembly as described previously.

2. Remove the two screws from the top of the metal cover and remove the cover.

3. Separate the cam from the circuit board by removing the four connecting screws from the circuit board.

4. The cam may be disconnected from its support blocks by removing the retaining ring from the shaft on the front of the switch and sliding the cam out of the support block. Be careful not to lose the small detent roller.

5. Defective switch contacts may be replaced by first unsoldering the damaged contacts and cleaning the solder from the holes in the circuit board. Next, position the new contacts in the holes so they are properly aligned in relation to the other switch contacts and the mating area on the circuit board (an alignment tool is provided in the cam switch repair kit). Solder the new contacts into place. Be sure that the spring ends of the contacts have adequate clearance from the circuit board.

6. Reassemble the cam switch assembly by reversing the previous process

Replacement of a Cam Switch Assembly

1 Connect the switch to the front panel

Fig. 4-5. Ceramic terminal strip assembly.

2. Connect the circuit board to the rear mounting bracket.

NOTE

Do not bend the circuit board while securing it to the rear mounting bracket. If the circuit board must be bent to secure the board to the rear mounting bracket, re-adjust the rear mounting bracket.

3. Reconnect the pin connections to the proper pins (see Fias. 4-6 through 4-28).

Rotary Switches. Individual wafers or mechanical parts of rotary switches are normally not replaceable. If a switch is defective, replace the entire assembly. Replacement switches can be ordered either wired or unwired; refer to the Electrical Parts List for the applicable part number.

When replacing a switch, tag the leads and switch terminals with corresponding identification tags as the leads are disconnected. Then, use the old switch as a guide for installing the new one. An alternative method is to draw a sketch of the switch layout and record the wire color at each terminal. When soldering to the new switch, be careful that the solder does not flow beyond the rivets of the switch terminals. Spring tension of the switch contact can be destroyed by excessive solder.

Semiconductor Replacement. Semiconductors should not be replaced unless they are actually defective. If re moved from their sockets during routine maintenance return them to their original sockets. Unnecessary replace ment or exchange of semiconductors may affect the calibration of this instrument. When semiconductors are replaced check the operation of that part of the instrument which may be affected.

CAUTION

POWER switch must be turned off before removing or replacing transistors.

Replacement semiconductors should be of the original type or a direct replacement. Fig. 4-2 shows the lead configuration of the semiconductors used in this instrument. Some plastic case transistors have lead configurations which

Page 94

Maintenance-Type 576

do not agree with those shown here. If a semiconductor is replaced by one which is made by a different manufacturer than the original, check the manufacturer's basing diagram for correct basing. All transistor sockets in this instrument are wired for the basing used for metal-case transistors. Use silicone grease when replacing transistors which have heat radiators or are mounted on the chassis.

WARNING

Handle silicone grease with care. Avoid getting silicone grease in the eyes. Wash hands thoroughly after use.

To prevent damage to the pins of the integrated circuits while they are being removed from their sockets, an extracting tool should be used. Such a tool is available from Tektronix, Inc. (Tektronix Part No. 003-0619-00.) If an integrated circuit is being removed without the use of an extracting tool, pull slowly and evenly on both ends of the device. If one end of the device disengages from the socket before the other, the pins can easily be damaged.

Relay Replacement. Relays like the one on the Step Generator circuit board (Tektronix Part No. 148-0044-00) may be turned either direction when connected to the circuit board.

Fuse Replacement. The power-line fuses are located on the rear panel in the Voltage Selector Assembly. See the electrical parts list for the values of the fuses.

Graticule Lamp Replacement. The graticule and readout title lamps may be removed from the rear of the graticule lamp circuit board by lifting the retainers from the contact of the lamp and pulling the lamp out from the rear.

Readout Lamp Replacement. Use the following procedure to replace a readout lamp:

1. Remove the bezel from the Type 576 front-panel.

2. Pull the readout assembly from the instrument.

3. Remove the metal cover from the readout assembly which has a burned out lamp.

CAUTION

Do not loosen or remove heat sinks or readout shelves when replacing readout lamps.

4. If the lamp to be replaced is connected to one of the rear readout lamp circuit boards, disconnect the readout logic circuit board from the readout assembly.

5. Unsolder the lamp leads of the burned out lamp from the back of the readout lamp circuit board. To determine which leads to unsolder, locate the pin on the readout logic circuit board which pertains to the burned out lamp, and follow the color-coded wire from that pin to the readout lamp circuit board.

6. Pull the readout lamp circuit board (and black plastic mounting) far enough away from its holder to replace the damaged lamp and replace the circuit board.

7. Solder the new lamp leads to the readout lamp circuit board.

8. Replace the readout lamp assembly cover (and read out logic circuit board if removed).

CeramicTerminal Strip Replacement. A complete ceramic terminal strip assembly is shown in Fig. 4-5. Replacement strips (including studs) and spacers are supplied under separate part numbers. However, the old spacers may be re-used if they are not damaged. The applicable Tektronix Part Numbers for the ceramic strips and spacers used in this instrument are given in the Mechanical Part List.

Page 95

To replace a ceramic terminal strips, use the following procedure.

Removal.

Replacement

strin completely

1. Unsolder all components and connections on the strip. To aid in replacing the strip, it may be advisable to mark each lead or draw a sketch showing the location of the components and connections.

2. Pry or pull the damaged strip from the chassis.

1 Place the spacers in the chassis holes

3. If the spacers come out with the strip, remove them from the stud pins for use on the new strip (spacers should be replaced if they are damaged).

2 Carefully press the stude of the strip into the spacers

until they are completely seated. If necessary use a soft

mallet and tap lightly directly over the stud to seat the

3. If the studs on the new ceramic strip are longer than those on the old one, cut off the excess length before the new strip is put in place.

4. Replace all components and connections. Observe the soldering precautions given under Soldering Techniques in this section.

Transformer Replacement. Be sure to replace only with a direct replacement Tektronix transformer.

Recalibration After Repair

After any electrical component has been replaced, the calibration of the associated circuit should be checked, as well as the calibration of other closely related circuits. Since the Power Supply affects all circuits, calibration of the entire instrument should be checked if work has been done in the Power Supply or if the power transformer has been replaced. The Performance Check and Calibration Procedure in Section 5 provides a means of checking instrument operation and making necessary adjustments.

TEST FIXTURE INTERFACE

The following two tables show pertinent information about the Test Fixture Interface located on the Type 576 front panel. This interface consists of four connectors: J360, J361, J362, J363 (see the Test Fixture Connectors schematic in the Diagrams section). The terminals on these connectors may be in one of two states: true or false. True and false are defined in terms of positive logic; the true state is the more positive of two voltage levels. Table 4-10 defines the true and false states of each usable terminal on these connectors in terms of voltage and current ranges. References to current are in terms of conventional current flow; that is, current flowing from a positive potential to a negative potential.

Explanation of the terms Sink and Source
INPUTS	OUTPUTS
Current Sinking	Current Sinking
When terminal accepts	When terminal accepts
current from external	current from external
circuit.	load.
Current Sourcing	Current Sourcing
When terminal supplies	When terminal supplies
current into external	current into external
circuit.	load.

TARI F 4.9

Page 96

TABLE 4-10 Test Fixture Interface

J360 Pin	J361 Pin	J362 Pin	J363 Pin	Description	Perf	ormance
				Input Signal Logic Levels	Input controls indicated function. 25 V maximum safe input.
					False	True
2				Step Generator Polarity Invert	Drive terminal to between 0 V (ground) and +0.8 V. Terminal sources 5 mA or less into external circuit.	Provide effective open circuit. Terminal must source 1 μA or less. Terminal open circuit voltage is +4 V to +5 V.
3				Step Generator Readout Off	Drive terminal to between 0 V (ground) and +1.5 V.
4				Beta Readout Off	Terminal sources 5 mA or
	15			Step Generator Read- out 10X Multiplier	less into external circuit.
			6	External Vertical Display Enable	Drive terminal to between 0 V (ground) and +1.5 V.	Provide effective open circuit. Terminal must source
		1		Collector Supply DC Mode Cuit.		100 μA or less. Terminal open circuit voltage is the +12.5 V supply.
			7	Vertical Readout Remote Control	Drive terminal to between 0 V (ground) and +1.5 V. Terminal sources 5 mA or less into external circuit. Changes convertible verti- cal outputs to inputs.	Provide effective open circuit. Terminal must source 1 μA or less. Terminal open circuit voltage is +4 V to +10 V.
			8	Vertical Readout Off	Drive terminal to between	Provide effective open circuit.
			9	Vertical Readout in Volts	0 V (ground) and +1.5 V. Terminal sources 5 mA or	Terminal must source 1 μA or less. Terminal open circuit
			10	Vertical Readout 10X Multiplier	less into external circuit.	voitage is +4 V to +5 V.
			19	External Horizontal Display Enable	Drive terminal to between 0 V (ground) and +1.5 V. Terminal sources 50 mA or less into external circuit.	Provide effective open circuit. Terminal must source 100 μA or less. Terminal open circuit voltage is the +12.5 V supply
			20	Horizontal Readout Remote Control	Drive terminal to between 0 V (ground) and +1.5 V. Terminal sources 5 mA or less into external circuit. Changes convertible horizontal outputs into inputs.	Provide effective open circuit. Terminal must source 1 μA or less. Terminal open circuit voltage is +4 V to +10 V.

Page 97

To replace a ceramic terminal strips, use the following rocedure.

Removal.

Replacement

strin completely

1. Unsolder all components and connections on the strip. To aid in replacing the strip, it may be advisable to mark each lead or draw a sketch showing the location of the components and connections.

2. Pry or pull the damaged strip from the chassis.

1 Place the spacers in the chassis holes

3. If the spacers come out with the strip, remove them from the stud pins for use on the new strip (spacers should be replaced if they are damaged).

2 Carefully press the study of the strip into the spacers

until they are completely seated. If necessary, use a soft

mallet and tap lightly directly over the stud to seat the

3. If the studs on the new ceramic strip are longer than those on the old one, cut off the excess length before the new strip is put in place.

4. Replace all components and connections. Observe the soldering precautions given under Soldering Techniques in this section.

Transformer Replacement. Be sure to replace only with a direct replacement Tektronix transformer.

After any electrical component has been replaced, the

Recalibration After Repair

calibration of the associated circuit should be checked, as well as the calibration of other closely related circuits. Since the Power Supply affects all circuits, calibration of the entire instrument should be checked if work has been done in the Power Supply or if the power transformer has been replaced. The Performance Check and Calibration Procedure in Section 5 provides a means of checking instrument operation and making necessary adjustments.

TEST FIXTURE INTERFACE

Explanation of the terms Sink and Source
INPUTS	OUTPUTS
Current Sinking	Current Sinking
When terminal accepts	When terminal accepts
current from external	current from external
circuit.	load.
Current Sourcing	Current Sourcing
When terminal supplies	When terminal supplies
current into external	current into external
circuit.	load.

TADLEAD

Page 98

TABLE 4-10

Test Fixture Interface

J360 Pin	J361 Pin	J362 Pin	J363 Pin	Description	Performance Input controls indicated function. 25 V maximum safe input.
		J362 Pin	J363 Pin	Input Signal Logic Levels
					False	True
2				Step Generator Polarity Invert	Drive terminal to between 0 V (ground) and +0.8 V. Terminal sources 5 mA or less into external circuit.	Provide effective open circuit. Terminal must source 1 μA or less. Terminal open circuit voltage is +4 V to +5 V.
3				Step Generator Readout Off	Drive terminal to between 0 V (ground) and +1.5 V.
4				Beta Readout Off	Terminal sources 5 mA or
	15			Step Generator Read- out 10X Multiplier	less into external circuit.
			6	External Vertical Display Enable	Drive terminal to between 0 V (ground) and +1.5 V.	Provide effective open circuit. Terminal must source
		1		Collector Supply DC Mode	Terminal sources 50 mA or less into external cir- cuit.	100 μA or less. Terminal open circuit voltage is the +12.5 V supply.
			7	Vertical Readout Remote Control	Drive terminal to between O V (ground) and +1.5 V. Terminal sources 5 mA or less into external circuit. Changes convertible verti- cal outputs to inputs.	Provide effective open circuit. Terminal must source 1 μA or less. Terminal open circuit voltage is +4 V to +10 V.
			8	Vertical Readout Off	Drive terminal to between	Provide effective open circuit. Terminal must source 1 µA or less. Terminal open circuit voltage is +4 V to +5 V.
			9	Vertical Readout in Volts	0 V (ground) and +1.5 V. Terminal sources 5 mA or
			10	Vertical Readout 10X Multiplier	less into external circuit.
			19	External Horizontal Display Enable	Drive terminal to between 0 V (ground) and +1.5 V. Terminal sources 50 mA or less into external circuit.	Provide effective open circuit. Terminal must source 100 µA or less. Terminal open circuit voltage is the +12.5 V supply
			20	Horizontal Readout Remote Control	Drive terminal to between 0 V (ground) and +1.5 V. Terminal sources 5 mA or less into external circuit. Changes convertible horizontal outputs into inputs.	Provide effective open circuit. Terminal must source 1 μA or less. Terminal open circuit voltage is +4 V to +10 V.

Page 99

ć,	J361 Pin	J362 Pin	J363 Pin	Description	Perform	nance
				Input Signal Logic Levels (cont)
					False	True
			21	Horizontal Readout Off	Drive terminal to between 0 V (ground) and +1.5 V.	Provide effective open circuit. Terminal must source 1 μA
			22	Horizontal Readout in Amps	Terminal sources 5 mA or less into external circuit.	or less. Terminal open circuit voltage is +4 V to +5 V.
				Output Signal Logic	Indicates state of instrum False, depending on settin	ent operation. Either True or g of instrument controls.
					False	True
	6			Negative Step Polarity	Drive terminal to between 0 V (ground) and +1.5 V. Terminal can sink 50 mA or less from external load.	Provide effective open circuit. Terminal must sink or source 100 μA or less. Terminal open circuit voltage is the +12.5 V supply.
	11			Step Generator Amplitude, 10 ^-1 Decade		Provide effective open circuit. Open circuit voltage is +4 V to +5 V. Terminal must
	12			Step Generator Amplitude, 10 ^-2 Decade		ternal load returned to volt- age between +5 V and +25 V, terminal sinks 0.1 µA or less.
_	13			Step Generator Amplitude 2X Switch Position
	14			Step Generator Amplitude 5X Switch Position
	16			Step Generator, 10 ^-4 or 10 ^-8 Decade or Volts
		2		Negative Collector Sweep Polarity		Provide effective open circuit. With external load
		3		15 V Range	-	returned to voltage of +25 V
		4		75 V Range	-	μA or less.
		5		350 V Range

ale

a notice

ALC: NO

in loss

and the second

Page 100

Maintenance—Type 576

J363 Pin	Description	Performance Outputs indicate state of instrument operation. When converted to inputs, they control the indicated readout and the 2X and 5X display amplifiers gains, but none of the other instrument functions.
	Convertible Outputs
	Vertical Logic Levels	Vertical outputs converted to inputs by False state at J363 pin 7 25 V maximum input voltage.
		Outpu	uts	In	puts
		False	True	Faise	True
1	Vertical 10 ^-1 Decade Inform- ation	Drive terminal to between 0 V and +1.5 V.	Provide ettec- tive open circuit voltage.	Drive terminal to between 0 V and +1.5 V.	Provide effective open circuit. Terminal must
2	Vertical 10 ^-2 Decade Inform- ation	Terminal can sink 50 mA or less from ex- ternal load.	Terminal open circuit voltage is +4 V to +5 V. Terminal must source 1 µA or less. If e x t e r n a l circuit load is returned to a voltage be- tween +5 V and +25 V, terminal sinks 0.1 µA or less.	Terminal sources 5 mA or less into external circuit.	source 1 µA or less. Terminal open circuit voltage is +4 V to +5 V.
3	Vertical 10 ^-4 Decade Inform- ation	Terminal can sink 50 mA or less from ex- ternal load.		Terminal sources 5 mA or less into external circuit.
4	Vertical 2X Switch Posi- tion or 50 mV/ DIV Deflec- tion Factor		Provide effective open circuit voltage. Open circuit voltage. Open	Drive terminal to between 0 V and +1.5 V. Terminal sources 50	Provide effective open circuit. Open circuit voltage is the +12.5 V supply.
5	Vertical 5X Switch Posi- tion or 125 mV/DIV DIV Deflec- tion Factor.		circuit voltage of the +12.5 V supply. Terminal must sink or source 100 μA or less	mA or less into external circuit.	Terminal must source 100 μA or less.

Tektronix 577, 576, 177 Service and user manual

PLEASE CHECK FOR CHANGE INFORMATION AT THE REAR OF THIS MANUAL.

576 CURVE-TRACER

INSTRUCTION MANUAL

INSTRUMENT SERIAL NUMBERS

TABLE OF CONTENTS

WARNING

Section 4 MAINTENANCE

age

Page

Section 6 ELECTRICAL PARTS LIST

Section 8 DIAGRAMS

CHANGE INFORMATION

OPERATORS SAFETY SUMMARY

TERMS

In This Manual

As Marked on Equipment

SYMBOLS

In This Manual

As Marked on Equipment

Power Source

Grounding the Product

Danger Arising From Loss of Ground

Use the Proper Fuse

Do Not Operate in Explosive Atmospheres

Do Not Operate Without Covers

SERVICING SAFETY SUMMARY

Do Not Service Alone

Use Care When Servicing With Power On

Power Source

WARNING NOTICE

Modification

WARNING

COVER MODIFICATION

NOTICE

SECTION 1 SPECIFICATION

TABLE 1-1 ELECTRICAL CHARACTERISTICS

Specification—Type 576

Specification-Type 576

Specification—Type 576

Specification-Type 576

TABLE 1-3 MECHANICAL CHARACTERISTICS

SECTION 2 OPERATING INSTRUCTIONS

General

INITIAL CONSIDERATIONS

Cooling

Operating Voltage and Frequency

Regulating Ranges

CAUTION

CONTROLS, CONNECTORS AND READOUT

CRT and Readout

Controls

Fig. 2-3. Rear-panel controls.

Display Sensitivity and Positioning

Collector Supply

Controls

Operating Instructions-Type 576

Liahts

Step Generator

Controls

Standard Test Fixture

Controls

Connectors

Rear Panel

FRONT PANEL COLORS

PRECAUTIONS

GENERAL DESCRIPTION OF INSTRUMENT OPERATION

FIRST TIME OPERATION

CRT and Readout Controls

Positioning Controls

Vertical and Horizontal Sensitivity

0111-00) into the right-hand set of accessory connectors located on the Standard Test Fixture.

Collector Supply

WARNING

The red light indicates that dangerous voltages may appear at the collector terminals of the Standard Test Fixture.

Fig. 2-9. Adjustment of LOOPING COMPENSATION control

Display Offset and Magnifier

Step Generator

Fig. 2-15. IC vs. IB, IB @ 50 µA per division.

Standard Test Fixture

Test Fixture Adapters¹