Keithley 1788, 177 Service manual

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Page 1

Instruction Manual

Model 177 Microvolt DMM

and

Model 1788 Battery Pack

01978, Keithley Instruments. Inc.

Cleveland, Ohio, U.S.A.

Document Number 29683

Page 2

Specifications

TEMPERATTURE COEFFlClENT VT-WC and m-55T.I:

*W305% + 0.1 di~itI/~C e~cepf *10.005% + 0.6 digifll°C on the

EXTENDED FREOUENCV ACCURACY ,45Hz--2OkW: i 10.7% + 15

diaitSl

TEtiPERATURE COEFFICIENT 10°-18pC Et ZW-55°C:

--2OkHz,: * ~0.05% + 2 digifs,PC

RESPONSE: True mot mean squsre

CREST FACTOR: 3

INPUT IMPEDANCE: IMO * 1% shunted by less than 75pF.

MnlyMUM *uOWABLE INPUT “OLT*GE: 1000” rms. ,400”

lO’+b maximum

CMRR Ilk0 unbalancel: SOdS at DC. 5OHz and SOHz

RESISTANCE

MAXIMVM ALLOWABLE INPUT: 350” peak

OPEN-CIRCUIT VOLTAGE: 5 volts

45Hz

peak

MAXIMUM INPUT: 2A. 250” DC or rms lfuse protected,

TEMPERATURE COEFFICIENT W-WC and 28D-550C,:

DC: f 10.2 digits)/°C except f 10.01% + 0.6 digitsl/“C on 2OpA range.

GENERAL DISPLAY: Five 0.5” LED digits, appropriate decimal point and polarity ins

dicatio” CONVERSION PERIOD: 400mS OVERRANGE INDICATION: Display blinks all zems above 19999 counts MAXlM”M COMMON MODE VOLTAGE: MOO” peak ANALOG OUTPUT: Output Voltage: IV = 10,000 county

ENVIRONMENT: Operating: O’C to SYc; 0% to 80% relative humidih/ up

CONNECTORS: In,,ut: Binding ,mst~ POWER: IOS- 125 or 210-250 volts (switch selected), gOpllOV available.

506-6OHz. 8 warts. Optional 6 hour battery pack, Model 1788 DIMENSIONS WEIGHT: 85mm high x 235mm wide x 275mm deep

13%” x 9%” x 10%“). Net weight: l.,kg (4 lb, ACCESSORlES *“VAILA.BLE:

Model ,010: Model ,017: Model ,301: Model 1SOOA: Model ,641: Model 1651: Model 1681: Model 1mzA: Model ,683: Model ,684: Model ,665: Model ,m,: Model ,779: Model 1788: Model 1792: Made, ,793:

Output Resistance: 50000

to ‘WC.

storage: --25oc to ~+65T

O”QJ”C smana jacks

Single Rack Mounfing Kif Dual Rack Mounting Kit Tempereture Probe High Voltage Probe 14OkVl Kelvin Test Leads 50-Ampere Current Shunt Clip-On Test Lead Set RF Probe Universal Test Lead Kit Hard Shell Carving Case Clamp~on AC Probe Genersl Purpose Test Lead Set Spare Paris Kit Rechargeable Battery Pack Isolated BCD OUtput lsalsted IEEE-488 Output

Specifications subject to change without notice.

Page 3

TABLE OF CONTENTS

Paragraoh

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

1.10

1.10.1

1.102

1.10.3

1.10.4

1.10.5

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

2.10

2.11

2.12

2.13

2.14

2.15

2.16

Title

SECTION I-GENERAL INFORMATION

Introduction .............................

Model 177 Features. ......................

Warranty Information .....................

ManualAddenda .........................

Safety Symbols and Terms. ................

Safety Precautions .......................

Specifications ...........................

Unpacking and Inspection

Scope of Model 177 Instruction Manual ......

Optional Accessories. .....................

Power Options. ........................

Cables and Connectors. .................

Probes and Shunts .....................

Carrying Case and Rack Mount ...........

Output Options ........................

.................

SECTION 2-OPERATION

Introduction.. .....................................................................

Safety Precautions for High Energy Circuits

Preparation for Use .................................................................

Operationon LinePower ............................................................

Operation on Battery Pack Power

Battery Charging ...................................................................

Operatinglnstructions ...............................................................

Zero Adjustment ...................................................................

DCVoltage Measurement ............................................................

ACVoltageMeasurement ............................................................

Resistance(O) Measurement .........................................................

DCCurrentMeasutement ............................................................

ACCurrentMeasurement ............................................................

TRMS Measurements (AC + DC) ....................................................

Analog Output

TiltBailAdjustment .................................................................

.....................................................................

.....................................................

............................................

......

Pan.3

l-l l-l 1-l 1-l 1-l 1-l

., 1-l

1-2

., .,

l-2 1-2 1-2 1-2 1-2 l-2 1-2

2-l 2-1 2-l 2-l 2-1 2-l 2-3 2-3 2-3 2-5 2-6 2-7 2-7 2-8 2-8 2-8

3.1

3.2

3.3

3.4

3.4.1

3.4.2

3.4.3

3.4.4

3.4.5

3.4.6

3.4.7

4.1

4.2

4.2.1

SECTION 3-PERFORMANCE VERIFICATION

Introduction.. .....................................................................

RecommendedTestEquipment

Environmental Condltlons.

Performance Verification Procedure

Initial Conditions

DC Voltage Accuracy Check (2V to 12OOV Ranges) DC Voltage Accuracy Check (20mV and 200mV Ranges)

ACVoltage Accuracy Check

Resistance (n Accuracy Check) DCCurrentAccuracyCheck

Analysis ........................................................................

.................................................................

.......................................................

...........................................................

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.......................................................

....................................................

.......................................................

SECTION 4-THEORY OF OPERATION

Introduction .......................................................................

OverallOperation ...................................................................

SignalConditioning ...............................................................

..............................

...........

........... 3-l

........... 3-1

........... 3-2

........... 3-3

3-l 3-l 3-l

3-3

4-l 4-l 4-1

Page 4

4.2.2

4.2.3

4.3

4.3.1

4.3.2

4.3.3

4.4

4.4.1

4.4.2

AIDConverter RangeSwitching

ACConverter

Scaling ....................................................................................

ACConversion ACCurrentMeasurements

DCSignalConditioning

InputAttenuation

Chopper ...................................................................................

..............................................................................

............................................................................

.................................................................................

..............................................................................

....................................................................

.........................................................................

...........................................................................

4-2 4-2 4-2 4-2 4-2 4-2 4-2 4-3 4-3

4.5

4.5.1

4.5.2

4.5.3

4.6

4.7

4.8

4.8.1

4.8.2

4.8.3

4.9

4.10

4.11

4.11.1

4.11.2

5.1

5.2

5.3

5.4

5.4.1

5.4.2

5.4.3

5.5

5.6

5.6.1

5.6.2

5.6.3

5.6.4

5.6.5

5.6.6

5.6.7

5.7

5.8

5.9

OhmsConversion

Floating

Chopper ...................................................................................

Adjustments and Input Overload Protection. AnalogOutput

Clock .......................................................................................

AIDConverter

Auto-Zero ..................................................................................

Signal-Interface

Reference-Integrate

Display ......................................................................................

Current Source

ACPowerSupply

Model17888atteryPack..

BatteryChargingCircuit

Battery Operation and Shutdown Circuit SECTION 5-MAINTENANCE

Introduction ..................................................................................

RecommendedTestEquipment

EnvironmentalCondttlons .........................................................................

CalibrationProcedure

Calibration Shield Installation

Warm-Up ..................................................................................

Calibration Instructions

Troubleshooting

Troubleshootingprocedure .....................................................................

Calibration Shield/Batten/ Pack Removal

LinePower

Battery Power

DisplayandA/DConverter ...................................................................

ACConverter

Chopper Amplifier and Ohms Source

CurrentShunts .............................................................................

Front Panel ZERO Knob Removal and Replacement FuseReplacement Model 1788 Battery Pack Installation.

.............................................................................

......................................................................

.....................................................

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.........................................................................

.............................................................................

.....................................................................

......................................................................

........................................................

..................................................................

..........................................................................

..................................................................

.......................................................................

...............................................................................

.......................................................

.................................................................................

..............................................................................

...............................................................................

...........................................................

................................................

.............................................................................

.............................................................

4-4 4-4 4-4 4-4 4-4 4-4 4-4 4-5 4-5 4-5 4-6 4-6 4-6 4-6 4-6

5-l 5-1 5-1 5-1 5-1 5-l 5-l 5-2 5-2 5-2 5-4 5-4 5-4 5-4

5-4 5-4 5-4 5-5 5-6

6.1

6.2

6.3

6.4

6.5

6.6

6.7

SECTION 6--REPLACEABLE PARTS

Introduction ..................................................................................

PartsList .....................................................................................

Orderinglnformation FactoryService.. ComponentLocationDrawings SchematicDiagrams MaintenanceKit

............................................................................

..............................................................................

...................................................................

.................................................................

...............................................................................

...........

6-l 6-l 6-l 6-l 6-1 6-l 6-l

Page 5

LIST OF FIGURES

Figure

1-l 2-1 2-2 2-3 3-1 4-l 4-2 4-3

5-l

5-2

5-3

5-4

6-l

6-2

6-3

6-4

6-5

6-6

Table

2-1

2-2

3-1

3-2 3-3

3-4

3-5 4-l 4-2 4-3 4-4 5-l

5-2 5-3 5-4

5-5 5-6

5-7

5-8

5-9

5-10

5-11

6-l

6-2

6-3

6-4

Title Page

Model177FrontPanel ..........................................................................

Model 177 Rear View of Standard Line Voltage Instrument Model 177 Rear View of Optional Line Voltage Instrument

Operating Controls .............................................................................

Test Circuitfor20mVDC Accuracy Check Model 177 Simplified Signal Flow Block Diagram Simplified Signal Conditioning

AfDConverterFunction .........................................................................

Test Point Locations

Integrator and Comparator Waveforms.

Front Panel Zero Knob Removal

BatteryPacklnstallation .........................................................................

Model177CoversandPanels .....................................................................

Model 177 PC-476, Component Location Drawing, Dwg. No. 294740, Display Board PC-475, Component Location Drawing, Dwg. No. 29652C

Model 1788 Battery Pack PC-451, Component Location Drawing, Dwg. No. 29007C Model 1788 Battery Pack, Schematic Diagram, Dwg. No. 29659C Model 1774% Digit Multimeter, Schematic Diagram, Dwg. No. 29658E

............................................................................

.................................................................... 4-3

..................................................................

..........................................................

.................................................... 4-l

............................................................

............................................ 2.2

............................................. 2-2

................................. 6-l 1

............................. 6-15

.....................................

................................

LIST OF TABLES

Title

Model 177 DMM Condensed Operating Instructions

Resistance Ranges .............................................................................

Recommended Test Equipment for Performance Verification DC Voltage Performance Check (2V to 1200V Ranges). ACVoltage Accuracy Check

Resistance Accuracy Check ......................................................................

DCCurrentAccuracyCheck

Range Switch Correlation ........................................................................

AC Converter Attenuation Amplification

DC Signal Conditioning Attenuation and Gain

OhmsConversion ..............................................................................

Recommended Test Equipment for Calibration Calibration Procedure Line Power Checks BatteryPowerChecks Display

A/DConverrer

ACConverter ..................................................................................

DC Attenuator and Chopper Amplifier OhmsSourceandResistors CurrantShunts Adjustment of Battery Charge Voltage

Model177SparePartsKit

Mother Board,

Modal 1788 Battery Pack, Parts List

Display Board,

....................................................................................... 5-8

............................................................................. 5-6

.................................................................................

..............................................................................

Parts List Parts List

.....................................................................

...........................................................

........................................................................... 5-2

...........................................................................

............................................................

..................................................................... 5-11

............................................................

....................................................................... 6-3

.........................................................................

..............................................................

......................................................................... 6-9

.................................................. 2-4

..........................................

..............................................

.......................................................

......................................................

1-O

2-5 3-2

4~5 5-3

5-4 5-5 5-5 6-2

...................... 6-16

6-17

6-19

Page

2-6

3-l 3-2 3-2 3-3 3-3

4-2 4-3 4-3 4-4

5-l

5-7

5-8 5-9

5-10

5-11 5-12

6-4 6-8

iii

Page 6

,’

1-o

Figure l-l. Model 177 Front Panel

Page 7

SECTION 1

GENERAL INFORMATION

1.1 INTRODUCTION

The Keithley Model 177 Microvolt DMM is a versatile, highly sensitive digital multimeter which is used for measurement of

DC and AC voltages, DC and AC currents, as well as

resistance. For a complete summary of ranges for each of these five functions, refer to the specifications at the front of this manual. Ranges and functions are easily selected with front panel pushbuttons, while connections for all functions are easily made with a single set of front panel input ter-

minals.

1.2 MODEL 177 FEATURES

1. 4% Digit LED Display-An easy to read 4% digit display shows 20,000 counts of information with automatic polari-

ty indication.

2. l~V/lmQ Resolution-The Model 177 is capable of reading DC voltages es low as 1wV and resistances down to 1mR.

3. Front Panel Zero-The front panel zaro control may be

used to compensate for thermal offsets or lead resistance

when making measurements.

4. Analog Output-An analog output of lV/lO,OOO counts is

available on the rear panel.

1.3 WARRANTY INFORMATION

Warranty information may be found inside the front cover of this manual. Should it become necessary to usa the warranty, contact your nearest Keithley representative or the factory to determine the correct course of action. Keithley Instru-

ments maintains service facilities in the United States, West Germany, Great Britain, France, the Netherlands, Switzerland and Austria. Information concerning the appli-

cation, operation or service of your instrument may be directed to the applications engineer at any of these locations. Check inside the front cover of this manual for ad-

dresses.

1.4 MANUAL ADDENDA

Information concerning improvements or changes to the instrument that occur after the printing of this manual will be covered in an addendum sheet packed with the instrument.

Be sure to review these changes before attempting to operate or service the instrument.

1.5 SAFETY SYMBOLS AND TERMS

The following safety symbols and terms are used in this

manual or may be found on the Model 177.

The symbol should refer to the operating instructions.

The symbol of 1OOOV or more may be found present on the terminals. Standard safety practice should be observed when such

dangerous voltages are encountered.

The WARNING heading used in this manual explains dangers that could result in personal injury or death if nor

handled properly. Be sure to read the WARNING informa-

tion carefully before performing the associated procedure.

The CAUTION heading is used in this manual explains

hazards that could damage the instrument.

1.6 SAFETY PRECAUTIONS

The following safety precautions should be observed before operating any digital multimeter.

1. This instrument is intended for use by qualified personnel who recognize shock hazards and are familiar with the

safetY precautions required to avoid possible injury. Read over the manual carefully before operating this instrument.

2. Exercise extreme caution when a shock hazard is present at the instrument’s input. The American National

Standards Institute (ANSI) states that a shock hazard exists when voltage levels greater than 30V rms or 42.4V peak are present. A good safety practice is to expect that hazardous voltage is present in any unknown circuit before measuring.

3. Inspect the test leads for possible wear, cracks or breaks before each use. If any defects are found, replace with test leads that have the same measure of safety as those supplied with the instrument.

4. For optimum safety do not touch the test leads of the instrument while power is applied to the circuit under tast. Turn the power off and discharge all capacitors, before connecting or disconnecting the instrument.

5. Do not touch any object which could provide a current path to the common side of the circuit under test or power line (earth) ground. Always make hands while standing on a dry, insulated surface, which is capable of withstanding the voltage being measured.

6. Exercise extreme precaution when tasting high energy power circuits (AC line or mains, etc.). Refer to the operation section of the manual.

7. Do not exceed the instrument’s maximum allowable input as defined in the specifications and operation section.

1.7 SPECIFICATIONS Detailed Modal 177 specifications are located at the front of

this manual.

on the instrument indicates that the user

on the instrument denotes that a potential

meawrements

with dry

l-l

Page 8

1.8 UNPACKING AND INSPECTION

1.10.3 Probes and Shunts

The Model 177 was carefully inspected, both mechanically and electrically, before shipment. Upon receiving the instru-

ment, carefully unpack it from the shipping carton and check for any obvious signs of physical damage that might have occurred during shipment. Report any damage to the shipping agent at once. Retain the original packing materials in case

reshipment becomes necessary. The following items are included with every Model 177 shipment.

1. Model 177 Micro\+t DMM

2. Model 177 Instruction Manual

3. Additional accessories as ordered.

1.9 SCOPE OF THE MODEL 177 INSTRUCTION

MANUAL

This manual contains information necessary to operate and

service both the Model 177 and the optional Model 1788 Sattery Pack and is divided into the following sections.

1. Section 2 contains operating information.

2. Information necessary to verify that instrument per-

formance is within specified accuracy is located in Section

Theory of operation is covered in Section 4.

4. Servicing information, including Model 1788 installation

instructions, may be found in Section 5.

5. Replaceable parts information, component layouts and schematic diagrams are located in Section 6.

1.10 OPTIONAL ACCESSORIES

1.10.1 Power Options

Modal 1600A High Voltage Probe-The Model 1600A

High Voltage Probe extends the measurable DC voltage range up to 40kV. It has a 1OOO:l division ratio, so that a reading of 1V on the DMM corresponds to IkV IlOOOV). The Model 1600A has a basic accuracy of lt25% and an input resistance of IOOOMQ.

Model 1651 SO-Ampere Shunt-The Model 1651

50.Ampere Shunt permits current measurements of up to 50A AC or DC. The shunt has a resistance of O.OOlQ * 1%. so that a 50A current will correspond to a reading of 50mV

I0.0500v).

Modal 1692A RF Probe-The Model 1682A RF Probe per-

mits measurement of AC voltages at frequencies of 20kHz to

250MHz. AC to DC transfer accuracy is Id6 at lV, and the

input voltage range is 0.25V to 15V rms.

Model 1685 Clamp-On AC Current Probe-The Model

1685 Clamp-On Current Probe permits measurement of AC current by clamping around a single conductor, eliminating the need to interrupt the current path. The Model 1685 has a current conversion ratio of O.lV/A with three ranges (2A.

20A, 200A). Accuracy is +4% at 60Hz If6% at 50Hz).

1.10.4 Carrying Case and Rack Mounts

Modal 1684 Carrying Case-The Model 1684 Carrying

Case is a hard vinyl case with a fitted foam insert to help pro-

tect the Model 177 from damage. There is also room in the

case for the instruction manual and small accessories.

Models 1010 and 1017 Rack Mounting Kits-The rack

mounting kits permit mounting one 11010) or two (1017) Model 177 DMMs in a 19 inch rack for convenient viewing.

The Model 177 can be powered by line voltage (105-125V at

50.60Hz or 210.250V at 50-GOHz--standard ranges) or the optional Model 1788 Rechargeable Battery Pack. (Optional

line voltage rangas are described in Section 2.1 The Model

1788 is available factory-installed or is field-installable. Instal-

lation and operating instructions are given in Section 2.

1.10.2 Cables and Connectors

Model 1881 Clip-On Test Lead

1.2m (48 in.1 leads with banana plugs at one end and springaction clip-on probes at the other end.

Modal 1683 Universal Test Lead Kit-This

two Im (40 in.) test leads and 14 screw-in adapter tips. The tips consist of two alligator tips with boots, four banana

plugs, phone tips, two spade lugs and four heavy duty tip plugs which permit connection of theModel 177 to virtually any source within its measurement range.

Set-This set contains two

kit contains

1-2

1.10.5 Output Options Model 1792 Isolated SCD Output-The Model 1792 con-

verts displayed reading to an electrically isolated, latched and buffered parallel BCD format. Output data includes sign,

overrange and busy. It is compatible with Model 177 serial number 14,500 and above, and can be either factory or field installed. Installation of the 1792 precludes installation of Models 1788 or 1793.

Model 1793 IEEE-488 Output-The Model 1793 converts

displayed readings to IEEE-488 bus compatible outputs to

permit automatic gathering of measurement data. Output in-

cludes 4% digit ASCII data, sign an overrange. It operates in either talk-only or addressable modes. The Model 1793 is compatible with Model 177s serial number 16,500 and above, and can be either factory or field installed. Installation of the

1793 precludes installation of the Model 1788 or 1792.

Page 9

SECTION 2

OPERATION

2.1 INTRODUCTION

This section provides information needed for preparation for use and operation of the Model 177 and Model 1788.

2.2 SAFETY PRECAUTIONS FOR HIGH ENERGY CIRCUITS

To optimize safety when measuring voltage in high energy distribution circuits, read and observe the directions in the following warning.

WARNING Dangerous arcs of an explosive nature in a high energy circuit can cause severe personal injury or death. If the mater is connected to a high energy circuit when sat to a current range, low resistance range or any other low impedance range, the circuit is virtually shorted. Dangerous arcing can result even when the mater is set to a voltage range if the minimum safety spacing is reduced.

When making measurements in high energy circuits use test

leads that meet the following requirements:

1. Test leads should be fully insulated.

2. Only use test leads that can be connected to the circuit (e.g. alligator or spade lugs) for a hands-off measurement.

3. Use test leads that do not reduce the arc protection by decreasing the voltage spacing between conductors or terminals.

Use the following sequence when testing power circuits:

1, De-energize the circuit using the regular installed connect-

disconnect device such as the circuit breaker, main switch, etc.

2. Attach the test leads to the circuit under test. Use appropriate safety rated leads for this application.

3. Set the DMM to the proper function and range.

4. Energize the circuit using the installed connect-disconnect device and make measurements without disconnecting the DMM.

5. De-energize the circuit using the installed connectdisconnect device.

6. Disconnect the test leads from the circuit under test.

2.3 PREPARATION FOR USE

The Model 177 is shipped ready-to-use on line power. The

instrument may also be powered from rechargeable batteries

(when the optional Model 1788 Rechargeable Battery Set is installed.)

2.4 OPERATION ON LINE POWER

The Model 177 DMM has a three-wire line cord which mates with third-wire grounded receptacles. Connect the insfru-

ment to AC line power as follows:

CAUTION Connect only to the line voltage selected. Application of incorrect voltage can damage the instrument.

Sat the LINE VOLTAGE switch on the back of the instru-

ment to correspond to the line voltage available. Standard ranges are 105V to 125V and 210V to 250V AC as shown in Figure 2-l. Optional ranges of 9OV to 11OV and 18OV to 220V AC are also available as shown in Figure 2-2. As indicated on their respective rear panels, the standard line voltage range instruments use an internal line fuse (F102) of 1/8A rating and the optional line voltage range instruments use a 3/16A fuse. See Section 5.

WARNING Ground the instrument through a property earth-grounded receptacle before operation. Failure to ground the instrument can result in savera injury or death in the avant of short circuit or malfunction.

2. Plug the power cord into a properly grounded outlat. Operate the Model 177 DMM as described in paragraph

2.7.

2.5 OPERATION ON BATTERY PACK POWER

The Model 177 DMM may also be operated from

rechargeable sealed lead-acid batteries contained in the optional Model 1788 Battery Pack. The battery pack will operate the Model 177 DMM for up to six hours. Circuits within the battery pack will automatically shut down the instrument when the battery charge is insufficient to maintain accurate readings. To install the Modal 1788, refer to Section

2.6 BATTERY CHARGING

The Modal 1788 Battery Pack contains an integral battery charger. To charge the battery pack, install the battew pack

in the Model 177 DMM as described above and proceed as

follows:

1. Connect the instrument to line power as described in paragraph 2.4.

2-1

Page 10

These adjustments are used only for calibration. They are not intended for adjustment during operation.

(JlOOS)

Figure 2-1. Rear View Of Standard Line Voltage Instrument

These adjustments are used only for calibration. They we not intended for adjustment during operation.

LINE VOLTAGE

SELECT SWITC

IP1007)

2-2

/+J

,JlOO,:

Figure 2-2. Rear View Of Optional Line Voltage Instrument

LINE VOLTAGL &x

SELECT SWITCH

(SlOll

-v

IP10071

Page 11

2. With the power switch off, the battery charge circuitry is automatically energized to charge the battery et the maximum rate. When the battev pack is first installed, or if it has completely discharged, allow it to charge for at least 14 hours in this condition.

NOTE

For maximum battery life, do not allow the battery pack to remain completely discharged. Constant charging will not harm either the battery pack or the instrument. The Model 177 may be operated up to six hours from fully charged batteries. However, since 10 charge/discharge cycles may be required to reach full batten/ capacity, less than six hours DMM operation can be expected when the battery pack is first installed.

3. When the Model 177 DMM is in use on line power, the battery charger maintains a trickle charge on the battery pack.

2.7 OPERATING INSTRUCTIONS

The basic operating instructions for the Model 177 DMM are outlined in the following steps, and condensed operating instructions are provided on the bottom cover of the instrument and contained in Table 2-l. These instructions should only be used after becoming completely familiar with the operation of the Model 177 through day-to-day use. Until this familiarity has been achieved, best performance and safest operation will be obtained by using the individual instructions provided in this section. Refer to Figure 2-3 and operate the

DMM es follows:

1. Turn on the power by depressing the ON/OFF pushbutton and allow a 10 minute warm-up time. Allow additional warm-up for zero stability on lowest DMM and Q ranges.

2. Select the function with the AC/DC, R, V, or A pushbuttons.

3. Select the range by depressing the appropriate pushbutton.

4. Connect the source to the INPUT terminals. Accessories described in Section 1 should be used as required.

CAUTION

Do not exceed the maximum input ratings

shown below.

DCV

ACV

DCA. ACA R

QOmV, ZOmV, ZVI: 450V rms continuous; 1200V peak momentan/, for up to eight

seconds per minute maximum.

(20.12OOV): 12OOV peak. ;I ;;;ges): 1OOOV rms; 1400V peak;

. (All Ranges): ZA, 250V DC or rms (fuse protected).

(All Ranges): 350V peak.

2.9 ZERO ADJUSTMENT

The front panel zero adjustment provides compensation for test lead resistance and thermal EMFs generated in the circuits connected to the DMM input terminals. The zero adjusrment is operative on the 20mV and 200mV ranges of DCV. 20 and 200R ranges and all DCA ranges. In general, the zero must be readjusted whenever the function is changed and the measurement is to be made on a range where the zero adjusts ment is operative. The accuracy specifications assume that zero is adjusted on the lowest range of the function. Where applicable, a specific zero adjustment instruction is provided in the description of how to make the particular function measurement.

2.9 DC VOLTAGE MEASUREMENT

The Model 177 measures DC voltages from l,lV/digit to

12OOV. The maximum displayed reading is 19999. Overrange is indicated by a flashing 0000 except on the 12COV range. On the 1200V range, the display can read beyond the maximum allowable input voltage. Use the Model 177 to measure DC volts as follows:

CAUTION

Do not exceed the maximum input voltage

ratings, or instrument damage may occur.

1. Turn on power with ON/OFF pushbunon and select DC

with the AC/DC pushbutton.

2. Select the desired range from the six ranges available. The decimal point is positioned by the range pushbuttons. The

1200V DC range is selected by the 1000 pushbutton.

NOTE

The 20M pushbutton is inoperative for DC volts. If this pushbutton is inadvertantly depressed. the Model 177 will read zero regardless of the voltage applied and the eight second per minute overload rating will apply.

3. Connect the signal to be measured between the INPUT HI and LO binding posts. The binding posts accept wires, spade lugs or banana plugs for ease of connecting the circuit to be measured. Low thermal cabling and connections are recommended for measurements on the 20mV and 200mV ranges.

4. For the top four ranges. merely observe the displayed digits, polarity sign and decimal point locations. The top four ranges are direct-reading in volts. Nominal settling time is located to within one digit of final reading.

5. For the 20mV and 200mV ranges, the front panel ZERO must be adjusted to obtain rated accuracy. This adjustment is necessary to compensate for thermal EMFs generated by the connections to the circuit to be measured. These voltages may be only a few microvolts or several tens of microvolts. The zero adjustment span is set up at the factory to allow at least f75,tV adjustment. To adjust zero, proceed as follows:

2-3

Page 12

Taba 2-1. Model 177 DMM Condensed Operating Instructions

Summary of Function, Ranges and Other lr

0.03% Rdg + 1 D

0.5% Rdg +15D lOOHz-10kHz

0.7% Rdg + 15D

0.2V Burden

lrmation

Max. Input

(Note 1)

1200v

Momentary

1OOOV RMS

10WHz

2A. 250V

DC or rms

(Note 4)

Front Panel

Zero

Yk?S

YC?S

2A. 250V

0.8% Rdg +15D

DC or rms

(Note 4)

350v

Peak

ANALOG OUTPUT: f2V full scale. 5k0 outout resistance Note 1: See manual fir detailed infbrmation.’ Note 2: Overrange is indicated by flashing 0000. Note 3: True root mean square, crest factor = 3. Note 4: Current fuse (installed internally) is 2A. 3AG normal blow. See Figure 5-4 for location.

2-4

Page 13

Polarity (Negative in indicated, positive is

implied when minus I-1 display is off.1

1. SET POWER ON 2. SELECT FUNCTION ‘3. SELECT RANGE 4. CONNECT SOURCE

Figure 2-3. Operating Controls

NOTE

Due to the long thermal time constant of the

20mV range zero, a one hour warm-up time may

be necessary to adjust zero to the final l@ setting. Typically, only a one to three microvolt zero shift can be expected during this warm-up

period, if the ambient temperature is within the

specified lfl” to 28% and the instrument has not

been subjected to temperature outside of this

range. Thus, since the expected zero shift is

both small and slow, normally zero can be adjusted and several measurements taken without

having to achieve the final zero setting.

Make connections to the Model 177 as described above. For the best performance, connections should

be made to the binding posts rather than using banana

plugs.

Set the Model 177 to the 20mV range.

Disconnect the leads at the circuit to be measured and short them.

Allow the thermal EMFs generated et the connections

to stabilize.

Adjust the front panel ZERO knob for a display indication of O.OOOmV (a flashing fO.OOlmV is permissible.)

NOTE The ZERO control operates only on the 20mV and 200mV ranges. It has no effect on the other DC voltage ran&.

Make the measurements by applying the signal and reading the mV on the display. Nominal settling time

for the 20mV range is three seconds to within one digit of final reading.

NOTE An overload input to the Model 177 may cause temporary zero shift due to thermal gradients.

The zero setting for the 20mV range will also be valid

for the 200mV range. Nominal setting time for the 200mV range is one second to within one digit of final

reading.

6. The optional Model 1600A High Voltage Probe can be used with the Model 177 to measure DC voltage up to 40kV. at reduced accuracy.

2.10 AC VOLTAGE MEASUREMENT

The Model 177 measures AC voltages from 1OrV to 1OOOV.

The instrument measures the true root mean square (TRMSI

of a signal within the frequency range of 45Hz to 20kHz. The maximum reading is 19999. Overrange is indicated by a flashing 0000 except on the 1OOOV range. On the 1OOOV range, the display can read beyond the maximum allowable input voltage. The maximum crest factor for rated accuracy is

3. AC accuracy is specified for 2000 counts and above. Nominal settling time for all AC voltage ranges is 2.5 second

to within 10 digits of final reading. Use the Model 177 DMM to measure AC volts as follows:

1. Turn on power and set the AC/DC pushbutton to the in or

AC position. Depress the V pushbutton.

NOTE The 20~ and 20M ranges are inoperative for AC volts. If the 20~ pushbutton is inadvenantly

2-5

Page 14

depressed, the display will read overrange, signalling the user to go to the next higher range. If 20M is depressed, the display will read zero regardless of the voltage applied. The method of calibrating the converter may yield an offset up to 125 digits with the Model 177 input shorted. This does not affect instrument accuracy.

2. Select the desired range from the five ranges available.

CAUTION MAXIMUM ALLOWABLE INPUTVOLTAGE (All

ranges):

IOOOV rme, 1400V peak. 107V*Hz maximum. Do not exceed the maximum rating. Instrument damage may occur.

3. Connect signal to be measured between INPUT HI and LO terminals. Observe the displayed digits and decimal point location. The 200mV range is direct-reading in mV and the remaining four ACV ranges are direct-reading in volts.

4. The crest factor (CFI is the ratio of the peak voltage to the rms voltage as follows:

CFrVPEAK

CAUTION MAXIMUM ALLOWABLE INPUTVOLTAGE (All ranaesl: 350V oeak. Do not exceed maximum rating. l&trument damage may occur.

2. Connect the circuit to be measured to the INPUT binding posts and select the desired range from the seven available.

Table 2-2. Resistance Ranges

Nominal

Range Maximum

Setting

200*

2ooll*

2kD 1.9999

20kD

200kD

2000kR 1999.9

20MD 19.999

*Front

Panel

Zero

Reading

19.999

199.99

19.999

199.99

Full Scale Voltage**

20mV

200mV

2v 2v 2v 2v 2v

All Ranges

Applied Current

1mA 1mA 1mA

1OOfiA

1 Oj.cA

O.lfiA

VRMS

NOTE

There will be some additional measurement error for signals with a crest factor greater than 3

fCF>3l.

Typical crest factors are as follows:

Sine Wave Square Wave

rriangular Wave Positive pulse train (duty cycle CF = 3 is 0.11)

5. The optional Model 1682A RF Probe can be used with the Model 177 to measure 0.25V to 15V rrn.s AC signals with a

frequency of 2OkHz to 250MHz (and above at reduced accuracy).

6. Refer to paragraph 2.14 for TRMS measurements of a signal with both AC and DC components.

CF = 1.4 CF = 1 CF = 1.7 CF = \/l/duty cycle

2.11 RESISTANCE KZ, MEASUREMENT

The Model 177 DMM measures resistance from lmD/digit to 20MD. See Table 2-2 for ranges. Nominal settling times to

within one digit of final reading are: three seconds on the 200 range; two seconds on the 2000kD and 20MD ranges; one second on the other four g ranges. Use the Model 177 to measure resistance as follows:

1. Turn on power and depress the R pushbutton.

?iii%gzm

il binding post treol IS negatrve.

3. Observe the displayed digits and decimal point to measure resistance using the 2k, 20k. 200k. 2000k and 20MR ranges. The full scale voltage drop for these ranges is 2V

which is sufficient to cause forward conduction of

semiconductor junctions. The HI (Red) terminal is negative. To measure a resistance in parallel with a semiconductor junction without turning on the junction, either reverse bias the junction or select the next higher D range. The latter method is possible because of the one

decade reduction of applied test current, but will result in a

measurement with 3% digit accuracy. It is suggested that the 2kg range be used for diode testing. This range has a nominal 1mA test current and the displayed reading is the

forward voltage drop in volts.

NOTE

The front panel ZERO control operates only on the 200 end 2OOD ranges. It has no effect on the other resistance ranges.

4. Before making measurements on the 2051 or 200R ranges, adjust front panel ZERO on the 20R range to compensate

for test lead resistance. Best performance will be obtained on the low ohm ranges when test connections are made to the binding posts, rather than using banana plugs. Adjust ZERO and make resistance measurements as follows:

2-6

Page 15

A. Select 200 range.

B. Disconnect the test leads at the circuit to be measured

and short them. If measurement is to be made right at the INPUT terminals (no test leads used) place a short, current as follows: such as a piece of copper wire, across the binding posts.

C. Adjust the front panel ZERO knob for a display indica-

tion of 0.000 *O.OOlG (flashing). The nominal ZERO adjustment span is 200mD.

D. Adjust front panel ZERO knob for a display indication of

O.OOO,rA * ,001 flashing.

2. After adjusting ZERO, use the Model 177 to measure DC

Do not install e larger capacity fuse then the one originally supplied L?Al. Current fuse FlOl (shown in Figure 5-4) protects the instrument against over-current.

NOTE

The specified accuracy for the 2OD and 2OOG

ranges assumes that ZERO was adiusted on the 20irange. Re-adjust zero on the 2dg range each time that a different set of leads is used or whenever measurements have been made on either the two lowest DC voltage ranges or any

DC current range. The zero setting for those

measurements will be different than the zero setting of ohms, Also, re-adjust zero whenever the

instrument is used outside the temperature

range of 18O to 28OC.

D. Reconnect the test leads to the circuit to be measured. E. Select either 2OD range or 2000 range. Read the

displayed digits and decimal point.

NOTE

An input overload to the Model 177 may cause a

temporary zero shift due to thermal gradients.

A. Select the desired range from the six ranges available.

8. Connect the circuit to be measured to the INPUT terminals.

C. Read the displayed polarity, digits and decimal point.

Select the next higher range if overrange is indicated.

2.13 AC CURRENT MEASUREMENT

The Model 177 measures AC current from 1OnAldigit to 2A. over five ranges. (The’ 20r~A and 20M ranges are not operative. See note below.1 The 200r~A range is direct-

reading in microamperes. The remaining AC current ranges

are direct-reading in milliamperes. The maximum reading is

19999. Overrange is indicated by a flashing 0000. Overload is protected by fuse FlOl, a 2A, 3AG normal-blow fuse. The instrument measures the true root mean square ITRMSj of

waveforms in the frequency range of 45 to 10kHz. Use the

Model 177 to measure AC current as follows:

1. Turn on power and set the AC/DC pushbunons to in or AC position. Depress the A pushbunon.

2.12 DC CURRENT MEASUREMENT

The Model 177 measures DC current from lnA/digit to 2A. over six ranges (the 20M range is not operative and the instrument will read zero if 20M pushbutton is depressed). The maximum reading is 19999. Overrange is indicated by a flashing 0000. Overload is protected by fuse FlOl, a 2A 3AG

normal-blow fuse. Nominal settling time for DC current ranges is one second to within one digit of final reading except three seconds on 20pA range.,

1. Before making DC current measurements, the front panel ZERO must be adjusted on the 20@ range. This adjustment is necessary to remove any offset that was introduced by adjusting ZERO for a low DC voltage measurementor a low g measurement. This adjustment will also be

necessary whenever the instrument is used outside of the temperature range of 18O to 28Y. The specified accuracy for the DC current ranges assumes that ZERO was ad-

justed on the 2OpA range. Adjust ZERO as follows:

A. Disconnect all circuits from the Model 177 INPUT ter-

minals. The INPUT terminals must have an open circuit~

_-...

8. Turn on power and set the AC/DC pushbunon to the out or DC position.

C. Depress A and 20~ pushbuttons.

Do not install a larger capacity fuse then the one supplied. Current fuse FlM (shown in Figure 5-41 protects the instrument against over current.

2. Connect the circuit to be measured to the INPUT terminals and select the desired range from the five ranges available.

The 20/1A and 20M ranges are not operative for AC current measurements. If the 20uA pushbutton is inadvertently depressed, an overrange will be indicated, signalling the user to go to the

next higher range. If the 20M pushbutton is depressed, the instrument will read zero.

3. Read the displayed digits and decimal point.

AC accuracy is specified for 2000 counts and above. The method of calibratina the converter may yield an offset up to 80 digits with the

Model 177 input shorted. This does not affect instrument accuracy. There will be some additional measurement error for signals with a crest

CAUTIONS

CAUTION

NOTE

2-7

Page 16

factor greater than 3 (CF>31.Refer to paragraph

2.10 for information on how to determine the crest factor of a waveform.

4. Refer to paragraph 2.14 for TRMS measurements of a signal with both AC and DC current components:

2.14 TRMS MEASUREMENTS (AC + DC)

The Model and does not measure the DC component. Use the Model

177

to measure TRMS of a signal which has both AC and DC

components as follows:

1. Measure and record the AC and DC components separatelV.

A. Refer to paragraph 2.9 for DC voltage measurement.

6. Refer to paragraph 2.10 for AC voltage measurement. C. Refer to paragraph 2.12 for DC current measurement. D. Refer to paragraph 2.13 for AC current measurement.

2. Compute the TRMS value using the following equation: ETRMS =“EDc~ + EACH OR lTRMS =‘IDC2 + lAC2

177

measures the AC component of a waveform

2.15 ANALOG OUTPUT

The rear panel accessible ANALOG OUTPUT provides a

f2V full scale DC signal IlOk counts = 1V). The ANALOG OUTPUT is operable for all instrument ranges and functions. The output polarity of the analog voltage is negative for the

ohms (0) function, positive for AC function and non-inverting for DC functions. The effective analog output resistance is 5kR (4kn in series with the HI output to protect the Model against externally applied voltage and 1 k0 between input LO and analog output LO to prevent a ground loop when con-

nection is made to a grounded load, oscilloscope or

recorder). The analog output voltage is compatible with most

modern analog recorders and may be used to determine signal changes with respect to time or other variables. With

respect to the signal input and analog output, the Model

acts as an amplifier (for mV signals), an attenuator (for kV signals) or a converter to DC volts (for AC current or

resistance signals). Output accuracy is the same as the display except on ohms; up to *0.05% error can be ex-

pected due to the ratio-metric method used. The analog out-

put floats at input LO. For this reason, do not connect a voltage source across INPUT LO and ANALOG LO. This will

result in a measurement error and may damage the Model

177

if the voltage is greater than 15V. When the instrument is

in an overrange condition, up to + 15V DC may be at the ANALOG OUTPUT dependent upon the function, range and

level of the input signal.

177

2.16 TILT SAIL ADJUSTMENT

The tilt bail of the Model strument to a convenient viewing height. To adjust the bail,

pull the bail out from each side of the case and rotate it to the desired position. Release the bail to allow it to lock into position.

177

may be used to elevate the in-

2-6

Page 17

SECTION 3

PERFORMANCE VERIFICATION

3.1 INTRODUCTION

Performance verification may be performed upon receipt of

the instrument to ensure that no damage or misadjustment

has occurred during transit. Verification may also be parformed whenever ther is question of the instrument’s accuracy, and following calibration, if desired.

NOTE

For instruments that are still under warranty (less than 12 months Since date of shipment), if the instrument’s performance falls outside specifications at any point, contact your Keithley representative or the factory immediately.

3.2 RECOMMENDED TEST EQUIPMENT

Recommended test equipment for performance verification is listed in Table 3-1. Alternate test equipment may be used. However, if the accuracy of the alternate test equipment is not at least IO times better than the instrument’s specifications, additional allowance must be made in the readings obtained. Some of the equipment listed in Table 3-I is not 10 times batter than the Model I77 specifications because such equipment is not readily available. In these instances, the verification procedures indicate the equipment manufacturer’s specified uncertainty, and include the uncsrtainty in determining the allowable reading for the Model 177.

3.3 ENVIRONMENTAL CONDITIONS

All measurements should be made at an ambient temperature within the range of 18” to 28OC (65” to 62OFl. and a relative

humidity of less than 80%.

3.4 PERFORMANCE VERIFICATION PROCEDURE

Use the following procedures to verify the basic accuracy of

the Model

measursments. If the instrument is out of specification at any

177

DMM for voltage, resistance and current

Table 3.1. Recommended Test Equipment For Perfomance Verification

point, perform a complete calibration as described in Section

5, unless the instrument is still under warranty.

NOTE

Performance verification should be performed by qualified personnel using accurate and reliable test equipment.

3.4.1 Initial Conditions

Before beginning the verification procedure the instrument must meet the following conditions:

1. If the instrument has been subjected to extremes of temperature, allow internal temperatures to stabilize for

one hour minimum at the environmental conditions specififed in paragraph 3.3

2. Turn on the Model I77 and allow it to warm up for one hour. The instrument may be operated from either line power or from battery pack power, as long as the battety pack has been fully charged as described in paragraph 2.6.

WARNING Some procedures require the usa of high voltage. Take care to prevent contact with live circuits which could causa electrical shock resulting in injury or death.

3.4.2 DC Voltage Accuracy Check (2V to 1200V Ranges)

I. Select DC voltage function with the AC/DC V push-

buttons.

2. Connect the DC calibrator to the instrument.

3. Select the 2V range. and apply positive 2VDC to the DMM. The reading must be within the limits specified in

Table 3-2.

4. Select each remaining range and apply required voltage

specified in Table 3-2. Verify that the reading is within specifications.

5. Repeat all checks with negative voltage.

Description

DC Calibrator AC Calibrator

AC Amplifier Decade Resistor

current source

1OOn Per Step 4-Terminal

Low Thermal Resistor

*0.002% or 2O@V

O.lV, 1v. IOV, IOOV 10.01% 1ooov @ 0.04%

1900, 1.9kQ. 19kQ. 190kn.

1.9MQ. IOMn, iO.OI% 100rA. lmA, lOmA, IOOmA, 1A

10:1 divider within 50 PPM

Mfr.

Fluke Fluke

Fluke

ESI

Fluke

ESI

3-l

Page 18

Table 3-2. DC Voltage Performance Check (2V to 1200V

Rangel

3.4.3 DC Voltage Accuracy Check (20mV and 200mV Rangesl

1. Select

2. Disconnect test leads at the DC calibrator and short them. Adjust Model 177 front panel ZERO for a display indication of O.OOOmV *O.OOlmV flashina.

3. Connect the DC calibrator and select 200mV range.

4. Set the DC calibrator to an output of +O.l9OOOOV.

5. Verify that the Model 177 reading is between + 189.89 to

calibrator.

6. Repeat steps 4 and 5 with negative voltage.

8. Connect the DC calibrator, low thermal resistor and

9. Temporarily disconnect the leads from the DC calibrator and short them. Adjust Model 177 front panel ZERO for a display indication of 0.000 * O.OOlmV flashing.

10. Set the DC calibrator to an output of +O.l9OOOOV.

11. Verify that the Model 177 readin is between + 18.987 ancl + IY.VIXnV. Note, that, the allowable reading includes *2 digits for DC calibrator uncertainty and * 1 digit for low thermal resistor uncertainty.

12. Repeat steps 10 and 11 with negative voltage.

DCV and 20mV range.

+ 190.11mV. Note that the allowable reading includes a i2 digit allowance for the uncertainty of the DC

Select 20mV M”Qc?.

Model 177 as shown in Figure 3-1.

~~^^_^ .,~

THERMAL R6SlSTOR

Figure 3-I. Test Circuit For 20mV DC Accuracy Check

3.4.4 AC Voltage Accuracy Check

1. Select AC voltage function with the AC/DC and V pushbuttons.

2. Connect the AC calibrator to the DMM. Set the calibrator frequency to 1 kHz.

3. Set the DMM to the 200mV range and apply 1OOmV AC to the DMM. The reading must be within the limits specified in Table 3-3.

4. Select the 2,20 and 200mV ranges and apply the required voltages as specified in Table 3-3. Verify that the readings are within spcifications.

5. To check 1OOOV range, connect the AC calibrator amplifier to the output of the AC calibrator per the manufacturer’s instructions. Connect the amplifier output to the Model 177 INPUT terminals. Set the AC calibrator

for amplifier output of lOOO.OOOV at 1kHz. Verify that the

DMM reading is within the specified limits in Table 3-3.

To check accuracy at 45kHz and 20kHz. select the 20V

range. Apply the voltage specified in Table 3-3 at 45Hr.

then repeat at 20kHz. Verify that the DMM readings are within the specified limits.

Table 3-3. AC Voltage Accuracy Check

Range

200mV

2ov

2oov

1ooov

2ov

Applied Voltage

@lkHz

lOO.OOmV 1 .oooov 1o.ooov 1oo.oov 1ooo.ov @45Hz 1o.ooov

Allowable Readings at

180 to 28Y.z

99.35 to 100.65mV

0.9935 to 1.0065V

9.935 to 10.065V

99.35 to 100.65V

993.5 to 1006.5V

9.915 to 10.085V

@2OkHz

2ov

1o.ooov

9.915 to 10.085V

3.4.5 Resistance KU Accuracy Check

1. Select resistance function by depressing n pushbuttons.

Select 2000 range.

3. Connect the decade resistor to the DMM.

4. Set the decade resistor to zero and compensate for lead resistance by adjusting front panel ZERO for a display in-

dication 00.10 f .OlQ flashing.

5. Set the decade resistor to 190% Verify that the reading for the 200R range is within the limits specified in Table 3.4.

Select the 2k0 ra”Qe.

Set the decade resistor to zero and measure the resistance of the test leads. Subtract this reading from the displayed reading in all of the following steps.

8. Set the decade resistor to 1.900kfI. Verify that the reading is within the limits specified in Table 3-4.

9. Continue by selecting the next range and measure the next

resistance as specified in Table 3-4. Test each item in the table and verify that each reading is within specifications.

3-2

Page 19

Table 3-4. Resistance Accuracy Check

Allowable Reading at

Range Resigtance

2000 1900 189.86 to 190.140

2kQ 1.900kR 1.8989 to 1.9011 kO

20kR

200kR

2000kO 1900.0k0 1898.9 to 1901.lkR *2 digits

20MR

*Manufacturer’s specified unceflainty of the decade resistor in digits. This uncertainty has been added to the specified accuracy of the Model 177 to obtain the allowable reading.

3.4.6 DC Current Accuracy Check

1. Select the DC current function with the AC/DC and A pushbuttons.

2. Select the 20cA range. With an open circuit at the INPUT terminals of the Model 177, adjust the front panel ZERO for a display indication of 0.000 1tO.00l~A flashing.

3. Connect the DC current source to the DMM.

4. Select each range and apply the required current as specified in Table 3-5. Verify that each reading is within specification.

Table 3-5. DC Current Accuracy Check

Applied Current

lOO.OO~A --

1 .OOOOmA

lO.OOOmA lOO.OOmA lOOO.OmA

0.9979 to 1.002imA

9.979 to 10.021mA

99.79 to 100.21mA

997.9 to 1002.lmA

19.000kfl

190.00kfI

lO.OOOMfl 9.988 to 10.012MR f 1 digit

180 to

18.989 to 19.011kR

189.89 to 190.11kfI

28%

3.4.7 Analysis

If the instrument is out of specified limits at any point in Table

3-2 through 3-5, calibrate the DMM as described in Section 5.

If the unit is still under warranty, refer to the ncate in

paraQraph 3.1.

It is not necessary to specifically check the 20R or 20uA ranaes. or a”” of the ACA ranaes. The circuit components that determine th& accuracy have been checked elsewhere in the verification procedure.

* 2 diQits + 2 disits + 2 digits +2 digits

NOTE

3-313-4

Page 20

Page 21

SECTION 4

THEORY OF OPERATION

4.1 INTRODUCTION

This section contains circuit descriptions for the Model 177

DMM and the optional Model 1788 Battery Pack. An overall block diagram of signal flow is provided in Figure 4-l. The

schematic diagrams are contained in Section 6 of this

manual. The Model 177 schematic is drawing number

29658E and schematic drawing number 29659C is for the

Model 1788.

4.2 OVERALL OPERATION

The Model 177 w?s a 2V (20,000 count) full scaleanalog-to-

digital (A/D) converter with a 4% digit multiplexed display. Signal conditioning permits the AID converter to accomodate full scale DC voltage and current measurements over seven ranges.

AC AMPLIFIER/

-4x=

R CURRENT OUTPUT

DC INPUT

DC AlTEN”ATOR/R SOURCE RESISTORS FUNCTION e RANGE

SWITCHING

il;-

0 SENSE

FEEDBACK

*ZVFS OUT

390Hz CHOPPER DRIVE

FRONT

PANEL

ZERO

OPTIONAL

SAlTERY

PACK

r-----7 I MODEL ’

I 1788

L-----A

CHOPPER

BUFFER/

AMPLIFIER

4.2.1 Signal Conditioning

Signal conditioning icludes: DC attenuation (on the 20, 200 and 1200V ranges), modulation and demodulation of the DC signal by the chopper buffer/amplifier with Xl00 and X10 gain Ion the 20 and 200mV ranges, respectively), AC atten-

uation (on the 20, 200 and 1OOOV ranges), AC amplification

(on the 200mV and 20V ranges), AC-to-DC conversion,

ohms source and conversion, and current shunts as shown in

Figure 4-l.

1. In the DCV mode, signal conditioning to the A/D converter consists of range and function switching, range resistors (attenuator) and the chopper buffer/amplifier. For all ranges, the DC input signal is attenuated/amplified to pro-

vide a *2V full scale output to the AID converter. In the

DCA mode, the voltage developed across the shunt

resistor is applied directly to the input of the chopper amplifier. A chopper gain of Xl0 is used for all ranges except 20A which uses X100.

DIGITAL

OUTPUT

TRMS AC

CONVERTER

c---7

L---J

DISPLAY

REFERENCE

IWkHz

CLOCK

OSClLLATOR

DIVIDER

Figure 4-1. Model 177 Simplified Signal Flow Block Diagram

4-1

Page 22

2. In the ACV mode, AC inputs for all ranges pass through the AC converter which consists of an amplifier/attenuator and a TRMS converter, as shown in Figure 4-2. The AC in-

put is scaled by the amplifier/attenuator to 2V rms full

scale for all ranges. The TRMS converter provides a

positive DC output signal which is proportional to the true root mean square AC signal. This DC signal is the input to

the A/D converter. In the ACA mode, the shunt voltage is

applied to the input of the AC converter. The amplifier/attenuator provides a x 10 gain for all AC current ranges.

3. Ohms conversion-Resistance measurements ara made by supplying a constant current from the ohms converter to the unknown resistor (Rx). The resulting voltage developed across the unknown resistor is proportional to its resistance, and this voltage is applied to the input of the chopper amplifier used for DC volts. The chopper amplifier output to the A/D converter is scaled to -2V full scale for all ohms ranges. Scaling of the ohms signal over the seven ranges is accomplished by using five constant current levels and the three gains of the chopper amplifier.

4.2.2 AID Converter

The A/D converter is a large scale integration (LSI)

ratiometric device. Converter output is a multiplexed five digit

number, in binary coded decimal IBCD) form which is equal to the ratio of the input voltage to the reference voltage. A separate clock circuit supplies a 1OOkHz timing input to the integrated circuit, which also multiplexes the BCD output. The full scale AID input for all ranges of the Model 177 is 2VDC. with the polarity determined by the function as follows: ACV and ACA. +2V; DCV and DCA. rt2V; Resistance (0). -2V.

4.2.3 Range Switching

It is important to note that the range switches on schematic 29658E are identified by the front panel marking for the

L2 ranges. The corresponding V and A ranges may either be determined from the instrument front panel or by using Table 4-l.

4.3 AC CONVERTER

When making AC voltage measurements, the AC converter

scales the input signal by appropriate attenuation or amplification, performs TRMS conversion and provides the equivalent positive DC level to the A/D for display. Input resistance for AC volts is 1MD IR107). Shunt capacitance is less than 75pF. Signal conditioning is as follows:

4.3.1 Scaling Scaling

schematic drawing number 29658E and summarized in Table

42. Scaling is performed by using a relay and FET switches to switch feedback resistors in the attenuator IUlOl) and the amplifier (U102). The actual gains used in attenuator UlOl

are 0.99, 0.0099 and 0.00099. Amplifier U102 gains are

nominally 1.003 and 10.03. The combined gain of UlOl and U102 is offset low to permit gain adjustment in the TRMS stage. The only adjustments provided in the attenuator and

amplifier stages are two high frequency compensation capacitors (Cl02 and C103). AC coupling is used at the input

and output of the attenuator and amplifier stages. Input

overload protection is provided by diodes (CRlOGand CR1071 and resistors R107 (1MQ. 2WI.

4.3.2 AC-to-DC conversion is performed b a monolithic TRMS

module lU103). Output V,

output filtering are done be ore the internal output buffer to

give a low impedance for the analog output. Potentiometer

R113 provides midband (10K count) gain adjustment and

R114 establishes output zero (1K count). Capacitor Cl08 is used in the averaging circuit, and Cl09 provides filtering as described above.

4.3.3 AC Current Measurements

For AC current measurements, the appropriate shunt resistor is placed in front of the AC converter. The 200mV range gain configuration is used for all current ranges.

4.4 DC SIGNAL

For DC voltage measurements, the input resistance is lOMO, which is established by all of the range resistors being connected in series to signal ground. On low voltage ranges, the

DC input is applied to the top of the resistive divider (range

resistor) and to the buffer amplifier input without attenuation. Also, the chopper amplifier has appropriate gain to provide a

f2V full scale output to the A/D. On high voltage ranges,

the DC signals are scaled down to *2V full scale by the

resistive divider and the chopper is used in the unity-gain

Ifollower) mode as a buffer. A summary of input attenuation and chopper amplifier gain is given in Table 4-3.

is performed in the first two stages, as shown on

AC Conversion

F =&. Averaging and

CONDITIONING

4-2

Table 4-l. Range Switch Correlation

Function

V 20mX 200m 2 20 200 1000** A 20/L*

*DC Only

*ACV 1000, DCV 1200

20 200 2k 20k 200k 2000k 20M

2oofl

Ranges

2m 20m 200m 2000m

Page 23

Table 4-2. Converter Attenuation and Amplification

**x100 = a101 On

**x 1000 = KlOl On

AC CONVERTER

Table

4-3. DC Signal Conditioning Attenuation

and

Gain

x 10

Xl Xl Xl Xl

Range

20mV

200mV

2ov

2oov

1200v

Input

Attenuation

+ 10

t 100

i 1000

Chopper

Gain

x 100

4.4.1 Input Attenuation

On the 20, 200 and 1200V ranges, the input signal is atten-

uated by the resistive divider to divide by 10, 100 and 1000, respectively. Depressing one of the above range pushbuttons, interrupts the unattenuated signal from the volts switch pin 17 and connects the wiper of the appropriate

range potentiometer to the input of the chopper. Division by

10, 100 and 1000 is accomplished by connecting the wiper of

R155, R156 or R157, respectively.

4.4.2 Chopper

The input signal to the chopper is filtered and applied to a

modulator circuit. The AC signal is then amplified and

demodulated. A final high gain DC amplifier provides a DC

signal to the AID converter and the analog output.

1. Modular Circuit-This circuit converts the input DC signal to an AC signal with a fundamental frequency component of approximately 390Hz. This frequency was chosen

because it reduces the amplitude of higher harmonics of

the 50Hz and 60Hz line frequencies, which minimizes

beating. The circuit utilizes a dual MOSFET (Q104A and

010413) connected in a series-shunt configuration to maintain the required high input impedance.

2. AC Amplifier-The AC amplifier uses a JFET-input opera-

tional amplifier (U108). The amplifier feedback network

provides a gain of approximately 133 at the modulating frequency of 390Hz. while maintaining a gain of one for amplifier (U108) DC offset voltages.

OHMS CONVERTER

Figure 4-2. Simplified Signal Conditioning

3. Demodulator Circuit-The demodulator is sychronized with the input modulator. A JFET (01051 with low onresistance is used to alternately attenuate and pass the signal present at the output of AC amplifier U108. This produces a “half-wave rectified” DC signal at the input of the integrator stage, that is inverted with respect to the chopper input signal.

4. DC Amplifier-Amplifier lU109) is connected as an integrator with an offset adjustment. U109 provides suffcient gain to bring the total open-loop DC gain to about one million. U109 drives the feedback divider network and the A/D converter, and provides the low output im-

pedance necessary to drive the analog output. Feedback capacitor (Cl381 was selected to provide nominal settling

time, while meeting NMR requirements. When the chop-

per is operating as a unity-gain follower, the DC signal prey sent at the output of U109 is the chopper feedback. This is the condition for the 2VDC range and above. On the 200mV and 20mV ranges, where chopper gains of 10 and

100 are required, the resistive divider feeds back a portion

of the output of U109 to provide the required gain.

5. Modulator-Demodulator Drive Circuit-CMOS inverters lUlllA and UlllF) provide opposite phase 0 to -15V square waves used to drive MOSFET modulator transistors Q104A and Q1048. lnverter UlllF also drives the

4-3

Page 24

demodulator JFET Q105. Resistors R118, R119 and R142 and capacitors Cl31 and Cl32 affect the rise and fall times of drive signals. R142 adjusts the rise and fall time of the drive signal to Q104A only, so that the total charge, both positive and negative, transfered to the input can be minimized. The frequency of the drive signal is determined by the clock circuit. Circuitry in UllO divides down a nominal clock frequency of 100kHz to produce 390Hz.

6. Adjustments and Input Protection-The front panel zero control CR2031 permits adjustment of the chopper feed-

back to compensate for input thermal EMFs. It functions only on ranges where chopper gain is greater than one. A

span of f75V is considered adequate; however, it is typical for R203 to provide a greater than 400V change as it is turned end-to-end. The span is skewed by R128 to

give best resolution in both DCV and n. Potentiometer

R146 provides a calibration adjustment to compensate 200mV range (X10 gain configuration) and R147 adjusts the Xl00 gain used on the 20mV range. Chopper input

resistor R143 limits the input current during momentan/ in-

put overloads to 12mA. which is then absorbed by the chopper load resistance (R145 and/or R149) or the power supplies through CR116 and CR117.

7. DC Current Measurements-As previously described, DC current measurements are made by placing the appropriate buffer/amplifier shunt resistor on the chopper input. A chopper gain of X10 is used for all current ranges

except 20A. which uses X100. The front panel zero control

(R203) is functional for all DC current ranges.

4.5 OHMS CONVERSION

The ohms converter contains two sections: a floating current source and a high input impedance buffer/amplifier. The chopper employed as a buffer/amplifier in DCV is also used as the high impedance buffer/amplifier for n. Refer to paragraph 4.4 for addition1 chopper theory.

4.5.1 Floatig Current Source

The floating current source involves a differential amplifier

W107) driven by the AID reference voltage and the chopper feedback voltage. This results in a constant voltage across the source resistance I = -V reference) which results in a constant current in the unknown resistance. One or more range resistors are always connected as the ohms source resistor IRS) when ohms function is selected. Five different constant current levels are supplied by changing the value of R, with the range pushbuttons. These levels are given in Table 4-4.

For n, INPUT HI terminal is negative with respect to INPUT

LO.

4.5.2 Chopper

to 200m0 of lead resistance. Settling time is determined primarily by chopper input (T = R C) which results in two seconds to full scale on the 200 (.047@F X 2Mfl and .0047wF X 20MW.

‘6

kQ and 20MO ranges.

Table 4-4. Ohms Conversion

4.5.3 Adjustments and Input Overload Protection

Two 0 source calibration adjustments are required. Potentiometer R162 compensates primarily for the tolerance of R,

(R158). while R159 compensates for ratio variations in the four gain resistors (R150 through R153). The protection network at the source output isolates the amplifier from positive

voltage overloads (Q103) and negative voltage overloads

lCR120) applied to INPUT HI. Transistor Q107 clamps the source input during overload. The ratio of the base to emitter

resistors on 0103 sets the open circuit voltage.

4.6 ANALOG OUTPUT

The rear panel ANALOG OUTPUT provides a -t2V full scale

DC output signal (10K counts = 1V). The analog output signal is available on all instrument functions and ranges, with a negative polarity on ohms W and a positive polarity on AC. The output is unbuffered, supplied by either the chopper or

the TRMS converter through 5kt7 effective resistance, with

1kR placed in the LO leg to prevent ground loops through IN-

PUT LO.

4.7

CLOCK

A single chip CMOS oscillator/ +2N package is used to generate the 100kHz A/D clock and the 390Hz chopper drive signals. The 1OOkHz OV to 5V signal drives the A/D and battery pack directly. The 390Hz signal is level shifted to OV to

-15V and split into two phases for driving the chopper FETs.

An RC adjustment (R142) provides chopper input bias cur-

rent compensation. Balancing and guarding is employed to

keep the drive signal out of the chopper AC amp stage.

4.8 A/D CONVERTER

For ohms, the full scale chopper output is -2V. Gain is employed on the 200 and 2OOQ ranges to give -2VFS out with the nominal 1mA source current. The front panel zero control functions on these two ranges, allowing compensation for up

4-4

The AID converter operates on the dual slope principle. The timing is divided into three periods as described below.

Page 25

4.8.1 Auto-Zero

4.8.3 Reference-Integrate

The auto-zero period (Figure 4-3) is 1OOmS in length, which corresponds to 10,000 clock pulses. During this period, the reference voltage W,,,) is stored on capacitor Cl%

Capacitor Cl15 stores V,,, + V,,, - V,,,.

4.82 Signal-Integrate

The signal-integrate period (Figure 4-3) is also 1OOmS in

length. The A/D input is buffered and integrated by U105.

Positive signals generate a negative-going ramp at the integrator ouput (pin 14). while negative signals produce a positive-going ramp. The level of the integrated signal at the end of the signal-integrate period is proportional to the average of the applied signal during this period. Since signal integration continues for 100mS. the A/D converter exhibits high normal mode rejection for AC signals in multiples of

IOHz, particularly the 50 and 60Hz line frequencies.

The reference-integrate period for a full scale input (Figure 4-3) is ZOOmS, or 20,000 counts in length. During this period, the integrator is returned to baseline level by applying a

reference voltage of a polarity opposite to that of the signal.

A positive-going ramp is obtained by grounding the buffer in-

put, while a negative-going ramp is produced by the integration of 2 x V,,, (that is, V,,, + the voltage stored in Cl 16). The time, or number of clock pulses, required for discharge is proportional to the signal input. Digital output is from latches

within U106 which store the number of clock pulses required for the integrator for the integrator to return to baseline level.

The maximum count during this period is 20,000 which cor-

responds to a discharge period of 200mS. or full scale input. For an input of lass than full scale, the A/D automatically reverts to auto-zaro for that period of the 200117s remaining after return to baseline level. V,,, is provided by a divider across a temperature-compensated zener diode. Operational amplifier U104 provides the zener with a self-regulating bias.

C. NEGATIVE REFERENCE INTEGRATE IZOk COUNTS AT

FULL SCALEI (POSITIVE INPUTS-TO AID)

6. SIGNAL INTEGRATE llOk COUNTS)

D. POSITIVE REFERENCE INTEGRATE IZOk COUNTS AT FULL

SCALE)

Figure 4-3. A/D Converter Function

4-5

Page 26

4.9 DISPLAY Five light-emitting diodes (LED) are driven by lJ203, which is

a CMOS BCD-to-seven segment decoder/driver with bipolar

current-sourcing outputs. Segment currents are. limited to approximately 20mA peak by resistor network R202. The LED readout is a multiplexed, common-cathode configuration

with Darlington array U202 sequentially sinking current from

each digit. Blanking of the overrange digit is accomplished by gates UlO4C and U104D. U104A and U104B ensure that CMOS-compatible levels are maintained on U104D. regardless of the loading of U202. The minus polarity readout is blanked on AC voltage and resistance ranges by normally

open contacts on the AC and 0 pushbuttons.

4.10 AC POWER SUPPLY

When the Model 177 is operated from AC line power, the power supply furnishes +5, + 15, and -15V from regulators VR,lOl, VR102 and VR103, respectively. Full-wave rectified AC from bridge rectifiers CR103 and CR104 is filtered by capacitors C120, Cl23 and Cl25 and is applied to the linear voltage regulators.

4.11 MODEL 1788 BAlTERY PACK

When the Model 1788 Battery Pack is installed in the Model

177. S102 must be set to the BAT position to provide additional secondan/ voltage for battery charging. SlO2 also switches the input to VRlOl from bridge rectifier CR103 to batteries BT301. Four 2V. 2.5 ampere-hour lead-acid calls supply approximately 9.8V at full charge. After six hours of use on battery power, the battery pack should be recharged to ensure long battery life.

4.11.1

Battery Charging Circuit

While the Model 177 is plugged into line power and the bat-

tery pack is installed, battery charging proceeds as follows:

I, Full-wave rectified from CR103 is applied to the

anode of 0301, which is an SCR which regulates charging voltage. When Q301 is triggered on by a sufficient gate-cathode voltage differential, the batteries receive charge. Charging continues as long as the bridge output voltage exceeds battery voltage by 1V or more. Resistor

R304 limits charging currant when recharging a set of completely discharge calls, a filtered positive output from CR104 (or T301) provides the necessary gate turn-on bias through I7306 and diode CR301. Resistor R303 ensures proper high-temperature operation of CI301.

2. When the battery voltages reach the present float voltages of 9.8V, zener VR301 conducts sufficient current to turn on Q302 and thus remove the gate trigger voltage from Q301. Float voltage is adjusted with R301. This is a factory adjustment which will normally not need field readjustment.

4.11.2 Battery Operation and Shutdown Circuit

The Model 177 operates as follows on battery power:

I. When the power is turned on, the batteries are connected

to the input of VRlOl to supply + 5V for the logic, display and the clock circuit. The clock output is applied to the A/D converter as described in paragraph 4.7, and U301 which is a divide-by-four binary counter. The outputs of U301 drive a DC-to-DC inverter which is sychronized to the A/D converter to filter out inverter noise. The 25kHz operating frequency is optimal for the small transformer size and results in low switching losses. Blocking capacitors C301 and C302 protect 0307 and 0308 from damage if the drive is lost. Two half-wave rectifiers (CR304 and CR3051 on the secondary of T301 provide rectified AC to filter capacitors C304 and C305, which provide power to

+ 15 and -15V regulators VR102 and VR103, respectively.

2. To prevent permanent loss of battery capacity caused by deep discharge, a shutdown circuit stops operation on battery power when the battery voltage drops below approximately 7.2V. Shutdown is performed by micropower voltage detector U302. The open-collector output (U302, pin 41 saturates low and turns off pass transistor Q309

when the input voltage

(at

U302. pin 31 drops below 1.15V (typical). Resistor R314 provides sufficient hysteresis to prevent discharge from resuming when the battery voltage rises following disconnection of the load.

4-6

Page 27

SECTION 5

MAINTENANCE

5.1 INTRODUCTION

This section contains information necessary to maintain the

Modal 177 and Model 1788 Battery Pack. Information concerning adjustment/calibration, troubleshooting, front panel zero knob removal and replacement, and fuse replacement are contained in this section. Calibration should be performed yearly (every 12 months) or whenever performance verification (see Section 3) indicates that the Model 177 is out of specifications. If any step in the calibration procedure cannot

be performed properly, refer to troubleshooting information

in this section, or contact your Keithley representative or the factory.

NOTE

Calibration should be performed by qualified personnel using accurate and reliable test equipment.

5.2 RECOMMENDED TEST EQUIPMENT

Recommended test equipment for calibration is listed in Table 5-1. Alternate test equipment may be used. However, the ac-

curacy of the alternate test equipment must be at least 10 times better than the Model 177 specifications, or equal to Table 5-l specifications.

5.3 ENVIRONMENTAL CONDITIONS

5.4.1 Calibrating Shield Installation

If the Modal 1788 Battery Pack is installed in the instrument it must be removed and the calibration shield reinstalled before calibration. If the calibration shield has been lost or misplaced, order Keithley Part Number 29473.

WARNING

Disconnect the line cord before removing

the cese cover.

1. Turn off the power and disconnect the line cord. Remove four screws from the bottom of the case and separate the top cover from the bottom cover.

2. Push back the ground clip from the upper side of the batten/ pack and remove the battery pack from the spacers.

3. Calibration may be performed on battery power as long as the battery pack is sufficiently charged. Leave the battery

pack plugged into the instrument, but set the battery pack behind the Model 177 on the bench or table. Ensure fhaf LINE/BAT switch lS102) is in BAT position.

4. Set the calibration shield in place on the spacers. The

shield should read correctly when viewed from the front of

the instrument.

5. Slide the ground clip over the top of the calibration shield

so that it contacts the upper surface of the shield.

6. If the battery power is not to be used, plug in the line cord

and position S102 to the LINE position if the batten, pack has been disconnected.

Calibration should be performed under laboratory conditions having an ambient temperature of 20°C to 26’C (68’F to

78°F). and a relative humidity of lass than 80%. If the instru-

ment has been subjected to temperatures outside of this range, or to higher humidity, allow one hour minimum for the instrument to stabilize at the specified environmental conditions before beginning the calibration procedure.

5.4 CALIBRATION PROCEDURE

Perform the following adjustments to calibrate the Model 177

and restore its operation to specified limits.

Table 5-1. Recommended Test Equipment For Calibration

Specification

O.lV, 1v. 1ov. 1oov. 1ooov

f0.002%

AC Calibrator

Decade Resistor 1OOR Per Step 4-Terminal Low Thermal Resistor

O.lV, lV, 1ov. 1oov.

fO.Ol%

5000, 1.9kQ. 190k0. *O.Ol%

1O:l divider within 50 PPM

(See Figure 3-l)

5.4.2 Warm-Up

Turn the Model 177 on and allow a one hour warm-up time.

5.4.3 Calibration Instructions

WARNING Some procedures require the use of high voltage. Take cere to prevent contact with live circuits which could ceuse electrical shock resulting in injury or death. Use en insulated tool when meking adjustments.

Mfr.

Fluke

ESI ESI

Model

343A 5200A RS725

SRlOlO

5-l

Page 28

1. Refer to Table 5-2 and perform the listed adjustments in the sequence indicated on the calibration shield by boxed numerals. The sequence must be followed exactly because the adjustments are interrelated and dependent on the preceding steps. The step sequence (box numerals) is also shown on schematic diagram 29658E.

2. If the indicated adjustment cannot be made to obtain the specified reading, refer to troubleshooting information in

this section.

5.6 TROUBLESHOOTING PROCEDURE

This section contains tables listing step-by-step checks of the major Model 177 circuits described in Section 4. Theory of Operation. The following steps outline the use of these tables

and provide instructions for preparing the Model 177 for troubleshooting. Read all of these steps carefully before troubleshooting the instrument.

5.6.1 Calibration Shield/Battery Peck Removal

5.5 TROUBLESHOOTING

The troubleshooting instructions contained in this section are

intended for qualified personnel having a basic understanding

of analog and digital electronic principles and components

used in a precision electronic test instrument. Instructions have been written to assist in isolating the defective circuit or subcircuit. Isolation of the specified defective component has been left to the technician.

NOTE

For instruments that are still under warranty (less than 12 months since date of shioment). if the instrument’s performance is outside of specifications at any point, contact your Keithley representative or the factory before attempting troubleshooting or repair, other than fuse replacement.

Table 5-2. Calibration Procedure

Step :unction Range

5 DC V 6 DC V 20mV 7 8 DC V

9 n 2k!l

10 0 2kfl 11 12 0 2kfl 1.9k0 13 n 200kn 190kR R156 14

15 16 DC v 1ooov + 1ooov R157 17 18 AC V 2v 19

20 21 22

DC v DC v DC v DC v

DC V

0 2kfl

DC V 2oov

DC V AC V AC V

AC V AC V AC V

2v Open

2v 2v Open 2v f1.9V

!OOmV + 190mV 20mV + 19mV

2ov -+ 19v

2v 2v

2oov

Input

Short Short

Short

50011

1.9kn 5oon

+ 19ov

.lV @ 1kHz R114

IV @ lktlz

.lV @I 1kHz R114

1V @ 1kHr

IOOV @ 20kHr Cl02

1V @ 20kHz

If the Model 1788 Battery Pack (or calibration shield) is installed, it must be removed to gain access to test points and circuit components for troubleshooting.

WARNING

Disconnect the line cord before removing

the case cover.

1. Turn off power and disconnect the line cord. Remove the four screws from the bottom of the case and separate the top cover from the bottom cover.

2. Push back the ground clip and remove either the calibration shield or battery pack from the spacers. If operation on battery power is to be checked, leave the battery pack plugged into the instrument, but set the battery pack behind the Model 177 on the bench or table.

Adjustment

Point

R163 R142 R163

R142 R134 R203

R146

R147

R162 R159 R162 R159

R139 R155

R113 R113 Cl03

Desired

Reading

oooo/-.oooo oooo/-.oooo oooo/-.oooo oooo/-.oooo

1.9000

3000/-.oooo

190.00

19.000

4999/.5000

1.9000

4999/.5000

1.9000

190.00

19.000

1000.0 .lOOO

1 .oooo

.lOOO

1 .oooo

100.00 1 .oooo

Test Equipment

None None None None

DC Calibrator None DC Calibrator DC Calibrator and 1O:l Divider Decade Resistor Decade Resistor Decade Resistor Decade Resistor Decade Resistor DC Calibrator DC Calibrator DC Calibrator 4C Calibrator 4C Calibrator 4C Calibrator 4C Calibrator 4C Calibrator

.4C Calibrator

5-2

Page 29

+15v,

-15v

+5v

Cl25 I-1

TPS’

TPlO’

F102

LINE FUSE

(1/8A)

&..-- TP5

R143

-(YELLOW I

CLIP

LEAD)

TPS

FiOl

CURRENT

FUSE (2A)

Figure 5-l. Test Point Locations

.SHUNTS

PANEL

CURRENT RlOl THRU

RlOS

Page 30

5.6.2

Line Power

In general, start troubleshooting with Table 5-3, line power checks, to verify that the power supplies are providing the correct voltages to the electronic components.

5.6.3 Battery Power If trouble occurs on battery power only, or if battery

operating time is substantially less than six hours after overnight charging, test the batteries and charging circuit per Table 5-4.

5.6.4 Display and A/D Converter

Proper operation of the AID converter and display should be verified before troubleshooting the signal conditioning circuits. Check the A/D converter and display per Table 5-5 and 5-6, respectively.

5.6.5

AC Converter

WARNING Some procedures in the following tables require the use of high voltege. Take cere to prevent contact with live circuits which could reuse electrical shock resulting in injury or death.

5.7 FRONT PANEL ZERO KNOB REMOVAL AND REPLACEMENT

The from panel ZERO knob will have to be removed if either the front panel or display is to be removed. To remove the knob, proceed as follows:

1, Carefully remove the end-cap (shown in Figure 5-31 using a

thin-bladed instrument.

2. Loosen the slotted screw and remove the knob from the

shaft.

3. Take care not to damage or lose either the end-cap or

knob. These items provide protection against electrical shock and must be installed when the instrument input is floating.

Problems with AC voltage or AC current ranges may involve

the AC converter. Check this circuit per Table 5-l. If the pro-

blem is only on AC current ranges, see below.

5.6.6 Chopper Amplifier and Ohms Source

Problems with DC voltage, DC current, or resistance ranges may involve the chopper amplifier. Check this circuit per

Table 5-8. After verifying chopper amplifier operation by

completing steps 1 through 10 of Table 5-8,

to Table 5-9 if resistance measurements are erratic. If problem is only on DC current ranges, see below.

NOTE

Dust, flux or other contamination will degrade

performance on resistance and DC voltage

ranges.

5.6.7 Current Shunts

If problems occur with current readings, check the current shunts and related circuitry per Table 5-10. It should be noted that, since the current shunts are common to both AC end

DC current, problems should exist on the same AC and DC current ranges if there is a fault in the current shunt circuitry.

NOTE

All measurements are referenced to mon (ground clip), unless otherwise noted in the Tables.

If a gross failure exists that indicates a possible blown fuse

(line power, battery pack, or current fuse) refer to paragraph

5.8 for fuse replacement instructions.

analog

com-

NOTE NOTE

If the display board has to be removed for If the display board has to be removed for

troubleshooting or repair, the front panel ZERO troubleshooting or repair, the front panel ZERO

knob will also have to be removed. knob will also have to be removed.

-1.2"

-,o"-~----~-

‘L-J-l--

( 100 ;

ImSEC! / InSEC I mSEC I

AUTO ShGNA; REFERENC: AUTO ZERO OF !

ZERO INTEGRATE INTEGRATE NEXT CONVERS,ON

Comparstor waveform Logic 1 during ramping)

200

100

Figure 5-2. Integrator end Comparator Waveforms

WARNING The ZERO potentiometer shaft is electrically connected to INPUT LO. Maintain INPUT

LO et ground potential while the ZERO knob or its cep is removed to prevent en

electrical shock hazard.

n I

I ,

5-4

Page 31

4. To replace the knob, reverse the preceding steps. Do not substitute any other knob. If the knob or its cap is lost or damaged, order only Keithley part number KN-41-l as a replacement.

Figure 5-3. F&t Panel Zero Knob Removal

5.8 FUSE REPLACEMENT

All fuses are located internally in the Model 177. To replace a

fuse, proceed as follows:

WARNING

Disconnect the line cord before removing

the caaa cover.

1, Turn off power and disconnect the line cord.

2. Turn the Model 177 bottom side up and loosen the four screws in the bottom cover. These screws are held captive by rubber O-rings.

3. Hold the top and bottom covars together to prevent their separation and turn the Modal 177 over to normal position.

Lift off the top covar.

CAUTION

Do not install fuses with higher ratings than

specified. Instrument damage may occur.

5. Replacement of battery pack fuse F301: A. Leave the battery pack in place and connected.

B. Remove F301, shown in Figure 5-4, and replace it with

a ZA, 25OV. 3AG fuse (Keithley part number FU-131.

BAITERV FUSE F301

LINE FUSE

FlOZ

E&,\

CONiUECTOR

1788,BATTERV

PACK

Figure 5.4. Battery Pack Installation

5-5

Page 32

6. Replacement of line power fuse F102: A. Once the top cover is removed, FlO2 is accessible

without removing any other components.

B. Remove FIOZ, shown in Figure 5-l. and replace it with

a l/EA, 25OV. 3AG. SLO-BLO fuse (Keithley part number FU-201 for standard line voltage units. Optional line voltage units with 90.IIOV and 190.2lOV ranges, use a 3/16A, 250V 3AG SLO-BLD fuse (Keithley part number FU-291.

7. Replacement of current fuse FlOl: A. Lift the calibration cover, or battery pack, off of the

spacers to gain access to the current fuse.

B. Remove FIOI, shown in Figure 5-l. and replace it with

a ZA, 25OV, 3AG fuse (Keithley part number FU-13).

C. Install calibration shield or battery pack on the spacers.

Be sure that the ground clip, shown in Figure 5-l. is

positioned on the top side of the shield or battery pack.

8. Reinstall the top cover.

5.9 MODEL 1788 BA-ITERY PACK INSTALLATION

WARNING

Disconnect the line cord before removing

the case ccwar.

1. Turn off the power and disconnect the line cord.

2. Turn the Model 177 bottom side up and loosen the four screws in the bottom cover. These screws are held cap-

tive by rubber O-rings.

3. Hold the top and bottom covers together to prevent their separation and turn the Model 177 over to normal position.

4. Lift off the top cover and the calibration shield. The four

plastic spacers must remain in place on the upright studs projecting through the main printed circuit board.

5. Set the BAT/LINE switch to the BAT position shown in

Figure 5-4. Note that the battery pack will not operate

properly if this switch is not in the BAT position.

6. Remove the fuse F301 on the battery pack.

7. Install the battery pack in the instrument so that it rests

on the plastic spacers. The ground clip must make contact with the upper side of the batten/ pack plate.

8. Carefully align the battery pack plug with connector P1004

on the circuit board. Push the plug firmly onto the connectar until the lip on the plug engages the lip of the connectar to lock the plug in place.

CAUTION

Make sure the connector is aligned so that

all pins mate properly, otherwise, damage to the Modal 177 and battery pack will

result.

9. Install the fuse F301. Reinstall top cover and secure with

four screws.

10. Charge the battery pack as described in paragraph 2.6.

step

**On optional line voltage units

Item/Component

SIOI Line Switch

SIOZ LINE/BAT Switch F102 Line Fuse

PI007 Line Cord

+ 5V Pad* VRlOl, IN CIZO22OO~F ( + )

+ 15V Pad*

VR102 IN, C12347OpF I+ j

-15V Pad*

VR103 IN, Cl25. 17OpF I-)

<On in

ain printed circuit board

Table 5-3. Line Power Checks

Required Condition

Must be set to 105.125V or 210.

250V as appropriate.**

Must be set to BAT for use with batten/ pack. Continuity Plugged into live receptacle.

Turn on power.

+5v *5%

+ 7V minimum.

+15v *lo%

+ 17.5V minimum.

-15v flO%

-17.5V minimum.

?a Figure 5-l).

(St

t to 90-I IOV or 180.22OV as appropriate.

Remarks

Output of VRlOl. Output of CR103, input to VRlOl. Output of VRIOZ, Output of CR104, input to VRIOZ. Output of VR103. Output of CR104, input to VR103 NOTE: Hot regulator may indicate shorted load.

5-6

Page 33

Table 5-4. Battery Power Checks

step

2 3 4 5

12A

13 14

Item/Component

S102 LINE/BAT Switch

PI007 Line Cord F301

BT301 Batteries

Each battery cell

voltage during charging.

0301 Anode c304 +

PI004 pin 8 or U301

0307 and 0308 Base Q307, Q308 Collector

Required Condition

Check AC line power per Table 5-3. Turn off power. Move to BAT. Plugged into live receptacle. Remove fuse and connect ammeter to fuse clip 0 to 500mA charging rate, varies with line voltage and battery state of charge.

Full charge is =9.8V over 4 cells. R301 adjusts charging rata (float

voltage)

1.5-3V for any cell. Full wave rectified voltage, 15 VDC

nominal.

+ 17.5V minimum.

Should saturate only when battery

approaches full charge.

8.2V zenar. Unplug line cord Et turn power on. IOOkHz 5V square wave.

+ 7V minimum

Square wave, f0.7V at 25kHz. Must oscillate from saturation to twice battery voltage (= 19V) at 25kHz

f 17.5V minimum ( *25V typical with

fully charged bat.)

Remarks

Charge circuit checks. No charge, see step 5A. Correct charging but short battery operating time, see step 6. If voltage is low and adjusts ment of R301 does not start charging, see steps 7 and following. If voltage is low and adjustment of

R301 does start charging, see Table 5-l 1 for adjustment of battery charge voltage.

High voltage or zero indicates damaged cell. Output of CR103

Output of CR104. Triggers Q301 gate thru R306 and

CR301 unless Q302 is on.

Discharge checks.

Clock input. If no input, see step 12A.

Battery voltage input to VRlOl.

Output of u301, -4

lnverier

lnverter Output, input to

VRIOZ and VR103

Page 34

Table 6-5. Display Checks

Step Item/Component Required Condition Remarks

2 +5V Pad* or JIOOI, +5v *5% If low, check per Table

pin 7

3 U202, pins 2, 6, 7, Digit drive. Low = Enabled

9 and 13

4 5 U203, pin 2

6 JIOOI, pin 2

‘On main printed circuit board. See Figure 5-l

Ki3; pins 1, 2, 6 HI = Enabled BCD input to U203 seg-

JIOOI, pin 4 J1002, pins 1, 11 &

Turn on power. Any function or range, except OHMS.

5-3

LED Cathode

ment decoder/drive

Negative-going signal lasting Leading digit suppres-

for 200 clock pulses.

Polarity Line (sign) HI = Off abled on AC an a. LO = -

Appropriate DP line high (on). Depress RANGE push-

sion.

Polarity output is dis-

buttons to check all

DPs.

Table 5-6. A/D Converter Checks

St;p 1 Item/Component

2 Display 3

TPI *

TPZ*

5 6 Display

TP4*

TP3*

9 U105, pin 11 10 U105, pin 14 1: U105, U105, pin pin 9 13 13 External Voltage

Source.

14 Display 15 TPl

16 U105, pin 14 17 U105, pin 2

+ l.OOV

Shot? TPI to TP2.

1 .OOOO k2 digits

0 to + 5V square wave at

IOOkHz f IOOHz.

+1.0 *O.lV +1.0 *0.1v

-1.2 f0.2V +1v

+1v

Apply + 1.9OOOV

1.9000 * 1 Digit

Remarks

Input to U106. Chopper out-

’ put.

Reference output. Connects reference output

to U106 input.

If steps 4 and 6 are correct

AID converter is functioning

properly. If not, continue with

step 7.

Clock input to U106.

Stored autozero voltage.

X-node voltage to integrator in U105. U105 integrator output voltage.

U105 buffer input. U105 buffer output. Calibration point.

If different, check U106 input. Input to U106. Integrator output. Comparator output.

5-8

*On main printed circuit board, see Figure 5.1,

Page 35

Table 5-7. AC Converter Checks

step 1 Item/Component

External voltage

source. TPlO*

TPEX U103 Pin 6 or

TPl*

External voltage

source.

TPIO

TP8

External voltage

SOUKB.

TPlO

External voltage

SOUKB.

Display

External voltage

source.

Display

External voltage

SO”Kt?.

Display

Required Condition

Turn on power. Select 2VAC range.

4pply IV rms at 1 kHz, .99V rms nominal

.993V rms nominal.

+1v

Select 20VAC range. Apply IOV rms at 1 kHz.

.099V rms nominal.

.993V rms nominal. Select IOOOVAC range. Apply IOOOOV rms at 1 kHz.

.99V rms nominal.

Select 200VAC range. Apply IOOV rms at 20kHz.

100.00 nominal.

Select 2VAC range. Apply IV rms

at 20kHz.

1 .OOOO nominal

Select IOOOVAC range. Apply IOOOV rms at 20kHz.

1000.0 * nominal.

Remarks VOTE: Full scale input on

311 ranges should produce = 2V rms output at TP8’.

Calibrated input. Dutput of UlOl and faed-

back components R108 and Cl03 (nominal gain ,991. output of u102. IQ102 on, nominal gain 1.0031. Output of U103. Gain of U103 adjusted to provide

+ 1VDC output for 1VAC I ‘h scale) input. Gain check of UIOI and U102. Nominally, .0099 IUlOl) and 10.03 lUlO21. Output of UlOl and feedback components R109. Cl04 and Cl101 Ion). Output of u102 (Q102 off). Calibrated input. Check gain of UlOl (nominal

.00099). Output of UlOl and feedback components KlOl, RI10 and Cl05 KIOI (Closed). Calibrated input.

High frequency response

(compensation C102, C103, ClO4). Calibrated input.

High frequency response.

(Compensation C102,

c1031.

High frequency response.

IC;yansation C102, C103.

External voltage

SOWCC?.

Display

*See Figure 5-l.

Select 2VAC range. Apply IV rms at 45Hz.

l.OOOOV * nominal.

Low frequency response. ClOl, C106, C107, C108, c109.

5-9

Page 36

Table 5-8. DC Attenuation end Chopper Amplifier Checks

Step

ltemlComponent

2 TP5. TP6”

External voltage

source.

RI43 (yellow wire

slide)“. TPl*

External voltage

source.

RI43

TPl

8 9

External voltage source. R143, TPl

External voltage

source. R143

12 13

External voltage source. R143

External voltage

source. RI43

Required Condition

Turn on power. Select 20mVDC range. Short input end adjust

F.P. Zero for + .OOOO on display.

=-7.5V DC (on DMM).

Apply + 19mV.

+ 19mV.

+ 1.9v

Select 200mVDC range. Apply.

+ 190mV. + 190mV

+1.9v

Select 2VDC range. Apply

+ 1.9v. +1.9v

Select 20VDC range. Apply

+ 19v. +1.9v

Select 200VDC range. Apply

+ 19ov. +1.9v

Select 1OOOV (12OOVI DC range. Apply + IOOOV.

+1v

*On maln pnnted circuit board, see Figure 5-l.

Remarks

NOTE: Insufficient zero

adjustment may indicated

leaky FET switches in Chopper Amplifier Circuit.

Chopper Drive. Signals are actually 0 to -15 square waves et 390Hz. A steady zero volt or -15V signal indicates a problem in the chopper drive or clock circuitry. Calibrated input.

Input to chopper amplifier

+ 1 attenuation (range resistors). Input to U106, chopper output ( x 100 gain). Calibrated input,

Input to chopper amplifier

+ 1 attenuation. Input to U106, chopper output t x 10 gain). Calibrated input.

+ 1 attenuation, x 1 chopper gain. Calibrated input.

f 10 attenuation (range resistors). Calibrated input.

f 100 attenuation (range resistors).

Calibrated input.

+ 1000 attenuation (range

resistors).

5-10

Page 37

Table 5-9. Ohms Source end Resistor Checks

Display

TP9”

INPUT HI to LO

1.9kl7 resistor.

Display

19kR resistor.

10 Display 11 190kC resistor.

12 Display

13 1900kD resistor.

14 Display

15 1OMD resistor 16 Display

*See Figure 5-l.

..w’IY..Y” -.,..“...-..

Check chopper amplifier operation per Table 5-7, steps 1 thru 10. Select 2kD range. Short Input. .OOOO *I digit.

-IV Approximately

Remove short end connect ammeter from INPUT HI to LO. Source current should be approximately

ImA, HI terminal negative. Remove ammeter end measure open

circuit voltage. Voltage must be

-2 to -5v.

Apply to INPUT.

1.9000 * 12 digits.

Apply to INPUT. Select 20kD range.

19.000 -f 12 digits.

Apply to INPUT. Select 200kR range.

190.00 f 12 digits.

Apply to INPUT. Select 2000kR range.

1900.0 f 12 digits.

Apply to INPUT. Select 20MI2 range.

10.000 * 12 digits.

NOTE: Reference loading by the ohms source does not affect D readout since AID converter is

ratiometric.

..” ..-...-

Inverted reference voltage

plus calibrated offset of

u107.

If incorrect, check R158 end switching to INPUT HI end chopper amplifier.

HI negative with respect to

LO. Display should be blink-

ing, indicating overrange.

Calibrated resistance.

Subtract test lead resistance

from reading. Checks

accuracy of R158 and feed-

beck loop to U107.

Calibrated resistance.

Source resistors: RI56 R154 (6975kDl. R157 (wiper).

Calibrated resistance.

Source resistors: R158, RI57 R156 (wiper), R154 l89.75kC.

8.975M). Calibrated resistance. Source resistors: R158, R157.

R156. RI55 fwiperl. R154, (all

except 6975MRl.

Calibrated resistance.

Source resistors: all R range

resistors. NOTE: To conveniently measure the resistance of all D range resistors, turn power off, set all function switches out end

measure resistance INPUT HI

to LO.

.___

Table 5.10. Current Shunt Checks

Step Item/Component Required Condition

Remarks

Apply a known % scale current end measure voltage across shunt.

( Cl;;ping must occur et

5-11

Page 38

Table 5-11. Adjustment of Battery Charae Voltaae

lponent

When

turn DMM on and

Required Condition

Instrument off. Turn full CCW (maximum charge rate). Monitor banery voltage for’9.8V.

cells reach 9.8V,

adjust to maintain 9.8V across BT301.

Remarks

Fully charged cells require several minutes to reach this level. Discharged cells require several hours.

CAUTION

Charging to 7 1OV for longer than 30 minutes will reduce battery life.

5-12

Page 39

SECTION 6

REPLACEABLE PARTS

6.1 INTRODUCTION

This section contains information for ordering replacement

parts.

6.2 PARTS LISTS

Table 6-2 contains a list of parts for the Model 177 mother board, Table 6-3 lists display board parts, end Table 6-4 lists

parts for the optional Modal 1766 Batten/ Pack. Each list is airanged in alphabetical order according to circuit designation. Mechanical parts ere listed on Figure 6-l.

6.3 ORDERING INFORMATION

To place en order or to obtain information concerning

replacement parts, contact your Keithley representative or the factors. See the inside front cover for addresses. When ordering, include the following information:

I. Instrument Model Number.

2. Instrument Serial Number.

3. Pert Description.

4. Circuit Designation (if applicable).

5. Keithley Pert Number.

6.4 FACTORY SERVICE

If the instrument is to be returned to the factory for sarvice. please complete the service form which follows this section

end return it with the instrument.

6.5 COMPONENT LOCATION

1. Model 177 PC-476 Component Layout No. 29474D.

2. Display Board PC-475 Component Layout No. 29652C.

3. Model 1766 Battery Peck PC-451 Component Layout No. 29007c.

DRAWINGS

6.6 SCHEMATIC DIAGRAMS

1. Model 1766 Battery Peck: Schematic No. 29659C.

2. Model 177 4% Digit Multimeter: Schematic No. 29656E.

6.7 MAINTENANCE KIT

A maintenance kit is available that contains a complement of spare parts that will maintain up to ten Model 177s. Specify

Model 1779 Spare Parts Kit when ordering. A list of the kit parts is given in Table 6-l.

6-1

Page 40

TOP COVER

26729E

LABEL

832 x 1

SCREW I41 84

294848

\\,I

-4.u

3ONT

4NEL

A444C

BINDING PO1

^ - - - - _ _

ELK BP-110

STS

KNH.1

LAblEL

MC-265

6-2

HANDLE

26729D

‘ALTERNATE PART #MC-264 FOR OPTIONAL LINE VOLTAGE UNITS

Figure 6-l. Model 177 Covers and Panels

Page 41

Table 6-1. Model 1779 Spare Parts Kit

my.

*An

Keithley Part No.

DD-30

DD-31

FU-13

5 2

FU-20

K-93

IC-102” IC-139”

1 1

IC-168”

IC-169

IC-197”

IC-203

IC-205

KN-41-1

1 1

LSI-11

LSI-12

RL-56

TF-80 TG-77

1 1

TG-93

TG-94” Static Protection Et Hand1

Schematic Number

DS202, 3,

4,5

DS201 FlOl

F102 Vi3101 u201 Ulll

U203

u202

UllO

u107, 109

U108

Front Panel zero

U106

u105

KlOl

R126

0101, 102,

105 Q103 Q104

Description

7-Segment Display

+ 1 Display Line Fuse Current Fuse

+ 5v Regulator CMOS NAND Gate IC CMOS Hex lnverter IC Segment Driver IC Digit Driver IC CMOS Binary Converter IC OP Amp IC OP Amp IC Knob

Loaic Processor IC An&a Processor IC Relay Thick Film Resistor 2N4392JFET

2N3439 Transistor

Dual MOSFET

ing

Page 42

Circui Desig.

Cl01 Cl02 Cl03 Cl04 Cl05 Cl06 Cl07 Cl08 Cl09 Cl10 Cl11 Cl12 Cl13 Cl14 Cl 15 Cl16 Cl17 Cl18 Cl19 Cl20 Cl21 Cl22 Cl23 Cl24 Cl25 Cl26 Cl27 Cl28 Cl29 Cl30 Cl31 Cl32 Cl33 Cl34 Cl35

Cl36 Cl37 Cl38

Cl39

Cl40

CR101 CR102 CR103 CR104 CR105 CR106 CR107 CR108 CR109 CR110

Table 6-2. Model 177 Mother Board. Parts List

Description

Capacitor, O.lpF, 1OOOV. Polvester Film Cabacitor; .25L115pF, ZO~bOV,.Teflon Trimmer

Capacitor, .25-l .5pF, ZOOOV, Teflon Trimmer Capacitor, IlOpF, 500VDC. f 1%. Silver Mica Capacitor, 11OOpF. 500VDC, *5%, Mica Capacitor, 33pF. 16VDC. f 10%. Aluminum Electrolytic Capacitor, 33~F, 16VDC, f lo%, Aluminum Electrolytic Capacitor, 1pF. lOOV, f 10%. Polyester Film Capacitor, lfiF, 1OOV. + 10%. Polvester Film NOT USED Capacitor, 22OOpF. 5OOV. Ceramic Disc Capacitor, 1OOpF. 1OOOV. Ceramic Disc NOT USED NOT USED Capacitor, lpF, 1OOV. f lo%, Polyester Film Capacitor, 4pF. 1OOV. 10%. Polyester Film Capacitor, .22pF, ZOOVDC, f lo%, Polyester Film Capacitor, .lZhF, lOOV, 10%. Polyester Film NOT USED Capacitor, ZZOOpF, 15V. Aluminum Electrolvtic Capacitor, 4.7pF. 25V, Aluminum Electrolytic Capacitor, 4.7pF. 25V, Aluminum Electrolvtic Capacitor, 470/~F, 35V. Aluminum Electrolytic Capacitor, 4.7/rF. 25V. Aluminum Electrolvtic C&∨ 47bF.’ 35V; Aluminum Electrolytic Capacitor, 1OpF. 25V. Aluminum Electrolytic NOT USED NOT USED NOT USED Capacitor, 1OOpF. lOOOV, Ceramic Disc Capacitor, 1OOpF. 63OV, 25%. Polystyrene Film Capacitor, IOOpF, 63OV, 25%. Polystvrene Film Capacitor, .0047&F, lOOV, Polystyrene Capacitor, .lZpF, IOOV, 10%. Polyester Film Capacitor, 1OOOpF. 5OOV. Polystyrene NOT USED NOT USED Capacitor, l+F, lOOV, 1096, Polyester Film Capacitor, lpF, 1OOV. 10%. Polyester Film Capacitor, .047pF, lOOV, Polystyrene

Bridge Rectifier, 1OOV. 1.5A Silicon Rectifier, 3A. 5OPIV. lN4139 Bridge Rectifier, lOOV, 1.5A Bridge Rectifier, 4OOV, 1.5A NOT USED Diode, Silicon, lN4148 Diode, Silicon, lN4148 NOT USED

NOT USED Diode, Silicon, IN4148

Location

Sch Pcb

83 E5

D3 D4

D4 c4

E3 G2

Bl B2

H3 G4

65 D8 c5

iti

85 c5

c7 87

E5 c5

D2 El

D8 c3

c5 c5

-12

Keithley

Part No.

c-285.1 C-184 C-184 C-278-110~ C-236.11OOpF C-321-33 c-321-33 c-294-1 c-294-1

C-22.22OOpF

C-64.100~

c-294-1 c-294-4 C-269-.22 c-294-.12

c-290-2200 c-314-4.7 c-314-4.7 C-289-470 c-314-4.7 C-289-470 c-314-10

C-64-100~ C-252-100~ C-252-100~ c-301-.0047 c-294-.12 C-138-1000~

c-294-2 c-294-1 c-301-.047

RF-36 RF-34 RF-36 RF-46

RF-28 RF-28

RF-28

6-4

Page 43

Table 6-2. Model 177 Mother Board. Parts List (Cont.1

Circuil Desig.

CR111 CR1 12 CR113 CR114 CR115 CR1 16 CR117 CR118 CR119 CR120

FlOl

F102

JlOOl J1002 J1003

J1004

J1005 J1008 J1007 J1008 J1009

KlOl

PlOOl

P1002

P1003

P1004

P1005 P1006 P1007

a101 a102 0103 0104 Q105 Q106 Q107 0108

Description

Diode. Silicon. lN4148 Diode; Silicon; lN4148 Diode, Silicon, lN4148 Diode, Silicon, lN4148 NOT USED NOT USED Diode, Silicon, lN4148 NOT USED NOT USED Rectifier, 1A. BOOV, lN4006

Fuse, 2A. 25OV, 3AG, Quick Fuse, Slo-Blo, l/BA, 25OV. 3AG (115V Version) Fuss, Slo-810, 3/16A, 250V (1OOV VersionJ

B-Pin Connector 1ZPin Connsctor Female Connector Connector Housing Binding Post, Black Binding Post, Red NOT USED 14-Pin Connector Contact

Relay, 5V. Reed Type B-Pin Connector

1ZPin Connector Connector, Male Connector, Male NOT USED NOT USED Line Cord

Transistor, N-Chan, JFET, 2N4392 Transistor, N-Chan, JFET, 2N4392 Transistor, NPN, Case TO-5, 2N3439 Transistor, Dual “P” Channel MOSFET B-Pin TO-77 Transistor, N-Chan JFET, 2N4392 Transistor, NPN, 2N5139 Transistor, NPN, Silicon, 2N3565 Transistor, N-Chan, JFET

LOCI

Sch

H4 B6

81 C8 C8

F6 G8 CB A3

c3 G6

G6 CB

C8 c3

D5 A7

Pcb

A2 82 82 03

84 D3

84 84

E5 Ez

E2 Al

c5 A3

F3 A4 A3

c5 c4 c3

Ei 82 c2 D3

Keithley Part No.

RF-28 RF-28 RF-28 RF-28

RF-28

RF-38 FU-13

FU-20 FU-29

(35-3564 CS-356-6 CS-288-3 CS-287-8 BP-11-O BP-11-Z

so-70

29316A

RL-56

(35-355-4 CS-355-6 CS-288-3 29467A

co-9 TG-77

TG-77 TG-93 TG-94 TG-77 TG-66 TG-39 TG-139

RlOl R102 R103 R104

R105

R106 R107 RlOB

R109

RllO

Rlll

R112

R113

Resistor, .ln, 7.5W, Wire Wound Resistor, 0.898n, 0.1%. Wire Wound Resistor, 90, .l%, 5W, Wire Wound Resistor, 90n. .I %, HW, Metal Film Resistor. 9000, .l%, l/BW, Metal Film

NOT USED Resistor, l.O05Ml?, 0.5%, ZW, Meral Film Resistor, SSOkQ, .l %, 1 /BW, Metal Film Resistor, S.S7kn, .l %M l/BW, Metal Film Resistor, 9910, .l%, l/BW, Metal Film Resistor, 90.3kR, ,196. l/BW Resistor, lOkn, .l%, l/BW Resistor. 5000. O.eW, Potentiometer

82 82

c2 c2

D3 D3 D3

D4 c4 E4

E2 D2

D2 D2

c5 c5 c5

E D4

R-262.. 1 R-310-.898 R-252-9 R-169-90 R-168-900

R-2841.005M R-176-990k R-176.9.37k R-176-991 R-176-90.3k R-176.IOk RP-97-500

Page 44

Table 6-2. Model 177 Mother Board, Parts List (Cont.1

Circuit Desig.

R114 R115 R116 R117 R118 Fill9 R120 R121 R122 R123 R124 R125 R126

R127 R128 R129 R130 R131 R132 R133 R134 R135 R136 R137 R138 R139

R140 R141 R142 R143 R144 R145 R146 R147 R148 R149 R150 R151 R152 R153 R154 R155 R156 R157

R158 R159 R160 R161 R162 R163 R184 R165

3escription 3esistor. 50kn, 10%. Cermet Trimmer

‘lOT USED \lOT USED qesistor. 27kQ. 5%. %W. Comoosition 3esistor; 4.32& l’&, 1 ISW qesistor, 4.99k0, 1%. 1/8W UOT USED +.?sistor, 3.9kn. lo%, ll2W. Composition ?esistor, lkR, 5%. SW, Composition UOT USED UOT USED qesistor, Thick Film qesistor, Thick Film UOT USED qesistor. 27kQ. 5%. Yaw. Comoosition UOT UiED qesistor, 6.49kfI. 1%. l/EW qesistor, 3.65kQ, 1 %, l/EW qesistor, 806Q, 1%, 1 IEW ?esistor, 2.15kn, O.l%, l/lOW Metal Film Resistor, 5On, 3/4W. POT Resistor, 4020, 0.1%. 1 I 1OW Resistor, 100kQ. l%, 1/8W Resistor, Selected with VR104 Resistor, 33.2kQ. f 1%. 1/8W Resistor, 50kn. 5%. Cermet Trimmer Resistor, 47kR. 5%. %W, Composition Resistor, 22M, 10%. %W Resistor, lkn, 10%. SW. Potentiometer Resistor, 100kR. I?%, 2W. Composition Resistor, 22kR. 5%, %W, Composition Resistor, 9220, 0.1%. %W, Metal Film Resistor, lOkR, 0.5W. Potentiometer Resistor, 1000, 0.5W. Potentiometer Resistor, 8.95kQ, 0.156, l/lOW. Metal Film Resistor, lOOn, .l%, l/lOW, Metal Film Resistor, 998kR, .l%, ‘/W, Metal Film Resistor, 998kn, .l%, %W, Metal Film Resistor, 998kQ, .l%, %W, Metal Film Resistor, 994kQ. .l%, %W, Metal Film Resistor, Thick Film Resistor, 5kn. 10%. Cermet Trimmer Resistor, 5000. 10%. Cermet Trimmer Resistor, 500, 10%. Cermet Trimmer Resistor, lk0, 0.1%. l/lOW Resistor, 10kQ. 10%. Cermet Trimmer NOT USED Resistor, 4.3MR. I/dW, Composition Resistor, 50kn, lo%,. Cermet Trimmer Resistor, ZOOkfl, .5W. Potentiometer Resistor, 200kR. 1%. 1/8W Resistor, lOOn, l%, 1/8W

Location Sch Pcb

A7 :2 87 :3 87 :2

SEV

G6 Jl 43

Jl 43

Hl 43

Hl A3

H2 A3

H3 82 Hl A3 F5 c4

Dl A6 !33 A6 83

87 43

85 D3

E5 c4

F5 c4

E5 c4

F5 c4

F6 c4

Gl D2

Dl 03

Dl 04 El D3 El D4

G2 D2

G2 c2

E5 c4 G2 D2 G2 c2

Keithley Pert No.

14 RP-97-6Ok

R-76-27k R-88.4.32k R-88-4.99k

R-1.3.9k

41 41 R-76-l k

33 TF-79

TF-80

R-76.27k

R-88.6.49k R-88.3.65k R-88-808 R-2632.15k RP-64-50 R-263-402 R-88.100k

27699A

R-88.33.2k

RP-97.50k R-76.47k R-76.22M RP-64-l k R-3-100k R-76.22k R-264-922 RP-97.10k RP-97-100 R-263.8.95k R-263-100

R-264-998k

R-264.998k

R-264.994k

TF-78

RP-97.5k RP-97-500 RP-97-50 R-263-l .OOOk RP-89.10k

R-76.4.3M RP-89.50k RP-97.200k R-88.200k R-88-100

6-6

Page 45

Table 6-2. Model 177 Mother Board, Parts List ICont.1

Circuit Desig.

R166 R167

SlOl

5102 s103

TlOl TlOl

UlOl u102 u103 u104 u105 U106 u107 U108 u109 UllO Ulll

VRlOl VR102 VRl03 VR104

YlOl

Description Resistor. 80.6kO. 1%. 1/8W

Resistor; lOOk0,‘1%,‘1/8W Switch, Line Selector

Switch, Line Battery

Switch, 12 Station Pushbutton

Transformer, Power (115, 23OV) Transformer, Power 1100, 2OOVl

IC, E-Pin Op-Amp JFET, TL081 IC, BI-FET, Op-Amp, LF351 IC, True RMS-TO-DC Converter, AD536 (TO-100) IC, E-Pin Op-Amp , 741 IC, 4% Digit Analog-Processor, 8052 IC, 4% Digit Logic-Processor, 7103 IC, Linear Op-Amp E-Pin, LM308 IC, J-FET Input Op-Amp, LF355 (selected) IC, Linear Op-Amp E-Pin, LM308 IC, CMOS 14.Stage Binary Converter, 4060 CMOSIMOS Hex Converter, 4089

Regulator, + 5V. 3-Term, TO-220. 7805

Regulator, + 15V. 500mA.78M15 Regulator, -15V. 500mA. 79M15 Regulator, Diode, Selected with R137

Clystal, Quartz fO.Ol%, 1OOkHz

Location

Sch

c7 D7 SEV

D6 D6

c4 D4 E4

H3 H4 Gl c5

D5 A6 A7

‘cb

A4 B4 E3

A5 A5

c5 c4 05 A2 A2 c2 c2 c3 c3

85 85 85

Keithley

Part No.

R-88.80.6k R-88.100k

SW-318 SW-397 294348

TR-168 TR-169

K-196 K-176

IC-172-l

IC-42 LSI-12 LSI-11 IC-203 IC-205 IC-203 IC-197 IC-139

IC-93 IC-194 IC-195

27699A

CR-8

6-7

Page 46

Circuii

Desig.

ET301 c301

C302

c303 c304 c305

CR301 CR302 CR303 CR304 CR305

F301 Q301

Q302 Q303 Q304 0305 0306 Q307 Q308 cl309 Q310

R301 R302 R303 R304 R305 R306 R307 R308 R309 R310 R311

R312 R313 R314 R315 R316

u301 U302

VR301

Table 6-3. Model 1786 Battery Peck, Parts List

Description

D Cells for BT301 (4 required) Capacitor, 4.7/1F, 20V

Capacitor, 4.7wF, 20V Capacitor, 1 .OwF, 250V Capacitor, 1OOpF. 35V Capacitor, 1OOpF. 35V

Diode, Silicon, lN4148 Diode, Silicon, lN4148 Diode, Silicon, lN4148 Diode, Silicon, lN4148 Diode, Silicon, lN4148

Fuse, 2A, 25OV, 3AG, Quick blow

Thyristor, SCR, 106Fl Transistor, NPN, 2N3904 Transistor, PNP, Silicon, TO-92 Case, 2N3905 Transistor, NPN, 2N3904 Transistor, NPN, 2N3904 Transistor, PNP, Silicon, 2N3905 Transistor, NPN, 2N3725 Transistor, NPN, 2N3725 Transistor, PNP, Silicon, MPS-U95 Transistor, PNP, Silicon, TO-92 Case, 2N3905

Resistor, 20kQ. lo%, Cermet Trimmer Resistor, 3300, 10%. ‘/IW. Composition Resistor, lkR, 10%. ‘/4W, Composition Resistor, 3.9kn. 20%. 3W. Wire Wound Resistor, 4.7k0, lo%, %W. Composition Resistor, 3.3kQ. lo%, XW, Composition Resistor, 82I2, 1056, XW, Composition Resistor, 820, 10%. SW, Composition Resistor, lOa, lo%, %W, Composition Resistor, 1On. lo%, %W. Composition Resistor, lOOk0, 1%. l/EW, Composition Resistor, lOOk0, 1%. l/EW, Composition Resistor, lOOkn, 1%. l/EW, Composition Resistor, 6.8M. 10%. 1/4W. Composition Resistor, 578kO. 1%. 1/8W Resistor, 1OOkn. 1%. 1/8W

IC, Dual D-Type Flip-Flop, 4013 IC, l.lV Micro-Power Detector, ICL8211

Regulator, 8.2V. Zener, 1 N785A

Location

Sch I

E2 D3

D4 E4 85 85

83 D4

D4 c5 c5

D3 03 c4 c4 D3 D4 c2 c2

83 B3 82 84 84 D4 D4 85 El5 D2

D2 D2 D2 D2 D2

c4 D2

Pcl

E3 E3 E3 F4 F3

D4 E3 E3 F4 F4

c3 c4

c3 D4 E4 E4 E4 E3 E3 D3 03

c3 c3 D4 D4 D3 c3 E3 E3 F4 F4 E3 E3 E3 E3 E3 E3

D3 E3

Keithley Pert No.

BA-33

c-179-4.7 c-179-4.7

C-256-l c-295-100 c-295-100

RF-28 RF-28 RF-28 RF-28 RF-28

FU-13

TG-132 TG-47 TG-53 TG-47 TG-47 TG-53 TG-131

TG-131 TG-133 TG-53

RP-97-20k

R-76-330

R-76-lk

R-268.3.9k

R-76.4.7k

R-76.3.3k

R-76-82

R-76-10

R-76.100k

R-78.100k R-76.100k R-78-6.8M R-88.576k R-88.100k

IC-103 IC-177

DZ-61

6-8

Page 47

Table 6-4. Display Board, Parts List

Circuit Desig. Description

C201 I Caoacitor. DS201

DS202 DS203 DS204 DS205

R201 R202 R203

u201 u202 U203

LED, Display, f 1 LED, Display, 7-Segment LED, Display, 7-Segment LED, Dsiplay, 7-Segment LED, Display, 7-Segment

Resistor, Thick Film Resistor, Thick Film Resistor, Potentiometer. 2W

IC, CMOS, Quad 2-Input NAND Gate. 4011 IC, Digit Driver, 75492

IC, Segment Driver, 4511

A2 E3

E2 E3

-Keithlay Part No.

c-314-4.7

DD-31 DD-30 DD-30 DD-30 DD-30

TF-62 TF-102-3 RP-117.50k

IC-102 IC-169 IC-168

6-9/6-10

Page 48

JlOO9,>

I-

Page 49

Figure 6.2. Model 177 PC476. Component Location

Drawing. Dwg. No. 29474D (Sheet 2 of 2)

6.13/6-14

Page 50

PC;475

R201,

/PI002

Figure 83. Display Board PC-475, Component Location Drawing. Dwg. No. 29652C

Page 51

Figure 8-4. Model 1778 Battev Pack PC-351 Component Location Drawing, Dwg. No. 29007C

Page 52

HIGHEST SCHEMATIC DESIGNATIONS USED

BTMl 1 cm5 J1004 , 0x0

“302 / “9301

1 CR303 1 F301 , R316 1 7301

Figure 8-5. Model 1788 Batten, Pack. Schematic Diagram. Dwg. No. 29659C

Page 53

Page 54

SERVICE FORM

Model No. Name Company Address City

List all control settings and describe problem.

Show a block diagram of your measurement system including all instruments connected (whether power

is turned on or not). Also describe signal source.

Serial No.

State

P.O. No. Date

Phone

-Zip

~. (Attach additional sheets as necessary.)

Where is the measurement being performed? (factory, controlled laboratory, out-of-doors, etc.)--~~~

What power line voltage is used?

Frequency?

Variation?

Any additional information. (If special modifications have been made by the user, please describe below.)

*Be sure to include your name and phone number on this service form

OF. Rel. Humidity?

Ambient Temperature?

Variation?

OF.

Other?

Keithley 1788, 177 Service manual

Specifications and Main Features

Frequently Asked Questions

User Manual