Tektronix 561b schematic

TECHNICAL MANUAL

OPERATOR’S, ORGANIZATIONAL, DIRECT SUPPORT, AND

GENERAL SUPPORT MAINTENANCE MANUAL

(INCLUDING REPAIR PARTS AND SPECIAL TOOLS LIST)

TM 9-6625-963-14-1

GRAPHICAL DISPLAY SYSTEM,

TEKTRONIX TYPE 561 SERIES

This copy is a reprint which includes current
pages from Change 1.

HEADQUARTERS, DEPARTMENT OF THE ARMY

OCTOBER 1972

NOTE

This manual is an authentication of the manufacture’s commercial literature which, through
usage, has been found to cover the data required to operate and maintain this equipment.
Since the manual was not prepared in accordance in with military specifications, the format
has not been structured to considered level of maintenance nor to include a formal section
on depot overhaul standards.

This manual contains copyrighted information. Reproduced by permission of Tektronix,
Incorporated. All rights reserved.

CHANGE TM 9-6625-963-14-1

Change 2

No. 2 HEADQUARTERS

DEPARTMENT OF THE ARMY

WASHINGTON, DC, 12 August 1986

OPERATOR’S ORGANIZATIONAL, DIRECT SUPPORT AND

GENERAL SUPPORT MAINTENANCE MANUAL,

INCLUDING REPAIR PARTS AND SPECIAL TOOLS LIST:

GRAPHICAL DISPLAY SYSTEM

TEKTRONIX TYPE 561 SERIES (NSN 4931-0(1-910-8164)

Current as of 16 April 1986

TM 9-6625-963-14-1, 11 October 1972, is changed as follows:

1. Remove old pages and insert new pages as indicated below. New or changed material is indicated by a vertical bar in the margin
of the page.

Remove pages Insert pages

0 -1 and 0 -2 0 -1 and 0 -2

12 - 1 through 12 - 11 12 - 1 through 12 - 16

2. File this change sheet in front of the publication for reference purposes.

By Order of the Secretary of the Army:

JOHN A. WICKHAM, JR.

General, United States Army

Chief of Staff

Official:

R. L. DILWORTH

Brigadier General, United States Army

The Adjutant General

Distribution:

To be distributed in accordance with DA Form 12-34C, Block No. 319, requirements for calibration procedures publications.

TM 9-6625-963-14-1

CHANGE 1

CHANGE HEADQUARTERS

DEPARTMENT OF THE ARMY

NO. 1 WASHINGTON, D.C. 20 MARCH 1975

TM 9-6625-963-14-1, 11 October 1972, is changed as follows:

1. The title is changed to read as shown above.

2. Remove old pages and insert new pages as indicated below. New or changed material is indicated by a vertical bar in the margin
of the page.

}

OPERATOR’S, ORGANIZATIONAL, DIRECT SUPPORT,

AND SUPPORT MAINTENANCE MANUAL,

INCLUDING REPAIR PARTS AND SPECIAL TOOLS LIST:

GRAPHICAL DISPLAY SYSTEM, TEKTRONIX

TYPE 561 SERIES (NSN 4931-00-910-8164)

Current as of 11 September 1974

Remove pages Insert pages

i and ii i and ii

12-1 through 12-11

3. File this change sheet in front of the publication for reference purposes.

TM 9-6625-963-14-1

TECHNICAL MANUAL HEADQUARTERS

DEPARTMENT OF THE ARMY

NO. 9-6625-963-14-1 Washington, D.C.

SECTION 0 INTRODUCTION................................................................................................................................................0-1

1A TYPE R561B SPECIFICATION......................................................................................................................1-1A

2A OPERATING INSTRUCTIONS R561B...........................................................................................................2-1A

3A CIRCUIT DESCRIPTION R561B....................................................................................................................3-1A

4A MAINTENANCE R561B..................................................................................................................................4-1A

5A PERFORMANCE CHECK VIRGULE MAINTENANCE CALIBRATION R561B...............................................5-1A

10 PREVENTIVE MAINTENANCE INSTRUCTIONS............................................................................................10-1

11 RACKMOUNTING............................................................................................................................................11-1

12 REPAIR PARTS LIST......................................................................................................................................12-1

Appendix A REFERENCES..................................................................................................................................................A-1

B BASIC ISSUE ITEMS LIST AND ITEMS TROOP INSTALLED OR AUTHORIZED LIST..................................B-1

C MAINTENANCE ALLOCATION CHART...........................................................................................................C-1

}

OPERATOR’S ORGANIZATIONAL, DIRECT SUPPORT, AND

GENERAL SUPPORT MAINTENANCE MANUAL

INCLUDING REPAIR PARTS SPECIAL TOOL LIST

GRAPHICAL DISPLAY SYSTEM,

TEKTRONIX TYPE 561 SERIES

(NSN 4931-00-910-8164)

1 CHARACTERISTICS RM561A...........................................................................................................................1-1

2 OPERATING INSTRUCTIONS RM561A............................................................................................................2-1

3 CIRCUIT DESCRIPTION RM561A....................................................................................................................3-1

4 MAINTENANCE RM561A..................................................................................................................................4-1

5 PERFORMANCE CHECK RM561A...................................................................................................................5-1

6 MAINTENANCE CALIBRATION RM561A..........................................................................................................6-1

PARTS LIST ABBREVIATIONS......................................................................................................................7-0.1

7 ELECTRICAL, PARTS LIST...............................................................................................................................7-1

8 MECHANICAL, PARTS LIST.............................................................................................................................8-1

9 DIAGRAMS........................................................................................................................................................9-1

11 October 1972

Page

Change 1 i

TM 9-6625-963-14-1

Figure 1-1A. Type RM561A Oscilloscope

ii

SECTION 0

INTRODUCTION

TM 9-6625-963-14-1

Scope

The manual includes installation and operation
instructions and covers organizational, direct support (DS),
and general support (GS) maintenance. It describes Graphical
Display System, Tektronix Type 561 Series. The basic issue
items list appears in appendix B. Appendix ’B is current as of
1 September 1972.

Indexes of Publications

DA Pam 310-4.

to determine if there are any new editions, changes, or
additional publications pertaining to the equipment.

DA Pam 310-7.

whether there are Modification Work Orders (MWO) pertaining
to the equipment.

Forms and Records

Refer to the latest issue of DA Pam 310-4

Refer to DA Pam 310-7 to determine

Reports of Maintenance and Unsatisfactory Equipment.

Use equipment forms and records in accordance with
instructions given in TM 38750.

Change 2 0-1

Report of Packaging and Handling Deficiencies

6). Fill out and forward DD Form 6 as prescribed in AR 700-8
(Army), NAVSUP Pub 378 (Navy), AFR 71-41 (Air Force), and
MCO P4030.29 (Marine Corps).

Discrepancy in Shipment Report.

Discrepancy in Shipment Report (SF 361) as prescribed in AR
55-38 (Army), NAV SUPINST 4610.33 (Navy), AFM 7-18 (Air
Force), and MCO P4610.19A (Marine Corps).

Fill out and forward

Reporting of Equipment Publication Improve

reporting of errors, omissions, and recommendations for
improving this publication by the individual user is encouraged.
Reports should be submitted on DA Form 2028
(Recommended Changes to Publications) and forwarded
direct to: Commander, U. S. Army TMDE Support Group,
ATTN: AMXTM-LML, Redstone Arsenal, AL 35898-5400.

(DD Form

ments. The

Fig. 1-1. Type R561B Oscilloscope.

0-2

SECTION 1

CHARACTERISTICS

General Information

The Tektronix Type RM561A Oscilloscope is essentially
an indicator unit with provision for two plug-in units. The plug­in unit in the right-hand opening controls the horizontal (X-axis)
deflection, and the plug-in unit in the left-hand opening
controls the vertical (Y-axis) deflection. The plug-in units con
be selected from any of the Tektronix ’2’ Series or ’3’ Series
groups to provide the desired oscilloscope performance.

Cathode-Ray Tube

Type - T5032-31-1 (rectangular ceramic-envelope).

Phosphor-P31.

Unblanking - Deflection type, dc-coupled, with grid
intensification.

Graticule - Variable edge lighted "no parallax" internal
graticule. Marked in 8 vertical and 10 horizontal divisions with
each major division divided into 5 minor divisions on
centerlines.

Accelerating voltage - 3.5 kv.

Useable viewing area - 8 divisions vertical by 10
divisions horizontal.

Deflection meters - 18.5 to 20.5 volts per centimeter
vertical, and 17.5 to 19.3 volts per centimeter horizontal.

Calibrator

Waveform - Square waves at line frequency.

RM561A

Output voltage - 1 millivolt to 100 volts, peak-to-peak, in 6
steps. The 1 v position provides an output of 0.1 volt into 50
ohms.

Accuracy - Peak-to-peak amplitude within 3% of indicated
voltage.

Rise-time - Typically 5 microseconds.

Power Supplies

Electronically regulated for stable operation with normal line
voltage variations and widely varying loads. The low voltage
supplies hold regulation within ± 1% of value.

Line voltage requirements - 105 to 125 volts, or 210 to 250
volts, rms, 50 to 60 cps, single-phase ac.

Fuse requirements - 3-amp slow-blowing type for 117 volts,

1.25-amp slow-blowing type for 234 volts.

Ventilation

Forced air cooled. Automatic-resetting thermal cutout
interrupts instrument power if internal temperature exceeds about
123° F.

Construction

Aluminum-alloy chassis.

Photo-etched anodized front panel.

Weight - 30-1/2 pounds, indicator unit only.

Dimensions - see Dimension Drawing at rear of manual.

1-1

SECTION 1A

TYPE R561B SPECIFICATION

Introduction

The Type R561B Oscilloscope is compatible with
Tektronix 2-Series and 3-Series plug-in units (see following
table and Section 2 for exceptions); thus, it con be used in a
variety of applications including differential, multi-trace, wide­band, delayed sweep, sampling and spectrum analysis.

This instrument will perform to the specifications listed in
this section in a laboratory environment with ambient

temperature range between 0°C and +50°C, except as
indicated. Warm-up time for rated accuracy is 5 minutes
(certain plug-ins may require additional warmup time). The
Performance Check instructions outlined in Section 5 provide
a convenient method of checking the performance of this
instrument.

ELECTRICAL CHARACTERISTICS

DISPLAY

Characteristics Performance

Plug-in Compatibility 2- and 3-Series plug-ins, except the

3S6, 3T6, 385 (horizontal only)
CRT Type Electrostatic deflection
Graticule Area 8 x 10 cm
Phosphor P31
Typical CRT
Accelerating Voltage

EXTERNAL INPUTS AND OUTPUTS

CRT Cathode Input
(AC Coupled)

Low - 3 dB
Frequency 1.8 kHz or less
Z Axis Modulation 10 V or less (P-P) gives useful

Maximum Input
Voltage

Calibrator

Output Voltages Into
High Impedance (1
MΩ or greater)

Into 50.0Ω

Current Loop 10mA DC or 10mA (P-P) square

3.5 kV

intensity variation

150 V

+4 mV, +40 mV, +0.4 V, +40 V

(ground to peak) square wave and

40 VDC (within 1-1/2%, +20°C to

+30° ;2 %, 0°C to +50°C

+2mV, +20mV, +0.2V (ground to

panel) square wave (within 1-1/2%,

+20°C to +30° C; 2%, 0° C to

+50°C

wave (within 1-1/2%, +20°C to

+30°C; 2%, 0°C to +50°C

Type R561B

Frequency 1 kHz within 1%
Duty Factor 48% to 52%
Rise-time and Fall-time

Line Voltage 115 VAC

Low 90 V to 110 V 180 V to 220 V
Medium 104 V to 126 V 208 V to 252 V

High 112 V to 136 V 224 V to 272 V
Line Frequency Range 48 Hz to 66 Hz
Maximum Power
Consumption at 115 VAC,
60 Hz

ENVIRONMENTAL CHARACTERISTICS

Characteristics Performance

Temperature

Non-operating

Operating
Altitude

Non-operating To 50,000 feet

Operating To 15,000 feet

Finish Lacquered aluminum panels.
Dimensions

Height

Width

Length

Accessories

Standard accessories supplied with the Type R561B are
listed on the last pullout page of the Mechanical Parts List
illustrations. For optional accessories available for use with this
instrument, see the current Tektronix, Inc. catalog.

1 µs or less at all voltages with
load capacitance of 100pF or
less, except 40 V, 2.5µs or less
at 40 V with load capacitance at
100 pF or less

POWER SUPPLY

230 VAC

186 W, 2.02 A

-40°C to +65°C
0°C to +50°C

PHYSICAL

Anodized aluminum front panel

≅ 7 inches
≅ 19 inches
≅ 20-1/2 inches

(A)

1-1A

SECTION 2

OPERATING INSTRUCTIONS

RM561A

Introduction

Before operating the Type RM561A Oscilloscope, be sure
that the instrument will cool properly, the proper line voltage is
used and the crt deflection potentials are correct. Function of
front-panel controls and operating considerations are given in
this section.

Cooling

A fan at the rear of the Type RM561A provides cooling.
The entire fan assembly is in a snap-in mounting that can be
mounted to exhaust air at the rear of the instrument or draw air
in at the rear and blow it throughout the instrument. Direction
of air flow con be changed to meet the operating conditions.

The Type RM561A can operate in ambient temperatures
up to 50°C. If the instrument overheats, the thermal cutout
turns off the power. When the internal temperature drops to a
safe operating level, power is automatically restored. If wired
for 117-volt operation, the fan will continue to operate when
the thermal cutout opens. On 234-volt operation, power for
the fan is turned off when the thermal cutout opens.

Line Voltage

The Type RM561A can be wired for either 117-volt or
234-volt operation. It will operate properly between 105 and
125 volts when wired for 117-volt operation and between 210
and 250 volts when wired for 234-volt operation. Converting
from one operating voltage to the other requires a change in
the power transformer primary connections, fan connections,
fuse and line cord plug. Figs. 2-1 and 2-2 indicate the
transformer primary and fan connections for

117-volt and 234-volt operation. A 3-amp slow-blow type fuse is
required for 117-volt operation and a 1.25-amp slow-blow type
fuse is required for 234-volt operation.

Front Panel Controls

The POWER ON switch and SCALE ILLUM. control permit
turning the instrument power on or off and provide adjustment of
the brightness of the graticule markings.

The FOCUS control adjusts the trace or spot focus.

The ASTIG. control is used in conjunction with the FOCUS
control, to assure proper focus over the entire crt display.

The INTENSITY control adjusts the crt display brightness.

The ALIGNMENT control permits electronic alignment of the
crt trace to match the horizontal graticule markings.

The 7-position CALIBRATOR switch determines the peak-to­peak amplitude of the signal at the CAL. OUT connector. It also
turns the Calibrator on or off.

Rear Panel Controls

The CRT CATHODE SELECTOR switch permits the operator
to select either (1) internal DUAL-TRACE CHOPPED BLANKING
to remove dual-trace chopped mode switching transients from the
crt display, or (2) Z-axis intensity modulation by external signals.

Operation

Operation of the Type RM561A Oscilloscope with two plug-in
units in place is much the same as that of a Tektronix oscilloscope
with corresponding vertical and horizontal deflection systems built
into the main frame. The plug-in

Fig. 2-1. Power transformer primary connections for
operation at (a) 117 volts or (b) 234 volts.

(A)(A)

Fig. 2-2. Fan terminal strip located near thermal cutout. (a) 117
volts, (b) 234 volts

.

2-1

Operating Instructions--Type RM561A

units are the vertical and horizontal deflection systems; their
outputs connect directly to the deflection plates of the cathode­ray tube. The plug-in units can be selected to give the Type
RM561A Oscilloscope the degree and type of performance
required for a particular application.

The controls and switches on the Type RM561A affect the
display; however, the plug-in units determine the major
characteristics of the system.

Calibrator Output

The Calibrator output signal of the Type RM561A provides
a convenient signal source for setting the gain of an amplifier
plug-in unit or the basic timing of a time-base plug-in unit. The
1 V position also provides a 0.1 volt amplitude signal when
connected to a 50-ohm system. This is very useful for
calibrating sampling plug-in units. See the plug-in unit
Instruction Manual for complete adjustment procedure.

In addition to these applications, the Calibrator output
signal can be used as a convenient square-wave signal source
for other applications.

NOTE
When using the Calibrator output
signal as a signal source for a system
sharing a common ground with the
Type RM561A (including plug-ins
used in the instrument) be sure that the
outer conductor of the CAL. OUT
connector is connected to the chassis
(or ground). Otherwise, the current
through the Calibrator ground resistor,
R899, may cause an incorrect
Calibrator output signal.

CRT CATHODE SELECTOR Switch

The CRT CATHODE SELECTOR switch provides two
modes of operation; CHOPPED BLANKING for dual-trace
amplifier plug-ins and EXT CRT CATHODE for intensity
modulation of the display.

The CRT CATHODE SELECTOR switch should be left in
the CHOPPED BLANKING position except when external
intensity modulation is used. For normal operation the
shorting plug should connect the EXT CRT CATHODE jack to
ground. Remove the plug for Z-axis modulation:

Display Combinations

The plug-in unit in the right opening of the Type RM561A
controls the horizontal (X-axis) deflection of the crt beam. The
unit in the left opening controls the vertical (Y-axis) deflection.
Conventional Display. To obtain the conventional display of
a horizontal sweep with vertical deflection by the input signal,
insert a time-base plug-in unit in the right-hand opening and

an amplifier unit in the left. If a vertical sweep is desired with the
input signal displayed horizontally, reverse the plug-ins. However,
in this manner, the sweep retrace will not be blanked. Retrace
blanking is provided only when a time-base unit is inserted in the
right side of the Type RM561A.

X-Y Display. To obtain an X-Y display, insert amplifier plug-in
units in both plug-in openings. Plug-in units with equal
characteristics should be used.

Intensity Modulated Display. The crt beam can be intensity
modulated, (Z-axis modulated) by applying a signal to the EXT
CRT CATHODE jack on the rear panel. Depending on the setting
of the INTENSITY control, the crt beam can be turned on with a
negative pulse, or off with a positive pulse.

To intensity modulate the display remove the shorting strap
from between the EXT CRT CATHODE and GND jacks. Set the
CRT CATHODE SELECTOR switch to the EXT CRT CATHODE
position and apply the modulating signal to the EXT CRT
CATHODE jack.

Changing Plug-in Units

Before inserting a plug-in unit into the Type RM561A
Oscilloscope, make sure the latching bar (bottom front) is not
pointing down., Then, push the plug-in unit all the way into the
opening. Turn the aluminum knob at the bottom center of the unit
clockwise until it is tight. To remove the unit, turn the knob
counterclockwise several turns and pull the unit out of the plug-in
compartment.

CAUTION
Although most plug-in units can be
inserted or removed without damage when
the power is on, best protection is
provided for all units by turning the power
off before changing units.

Different plug-in units apply slightly different dc voltages to
the crt deflection plates. The Type RM561A crt has higher
horizontal deflection sensitivity than vertical deflection sensitivity.
Also, changing one plug-in unit con affect the accuracy of the
other unit installed. Therefore, if one or both of the units are
replaced, check the gain of both units. If a plug-in needs
adjustment, follow the directions in the applicable Instruction
Manual to adjust gain or sweep timing.

When the plug-in units are changed, the FOCUS and ASTIG,
controls on the Type RM561A may need readjustment.

The Type RM561A can be operated with only one plug-in unit
if desired. For example, moving film recording may be used in
place of a sweep plug-in unit. To operate with only one plug-in
unit, it will be necessary to elevate the unconnected crt deflection
plates to about +170 to +210 volts dc vertical or +150 to +180
volts dc horizontal. This will provide proper action of the FOCUS
and ASTIG. controls.

(A)(A)

2-2

SECTION 2A

OPERATING INSTRUCTIONS R561B

Type R561B

Introduction

To effectively use the Type R561B, the operation and
capabilities of the instrument must be understood. This
section of the manual describes the operation of the front­and rear-panel controls and connectors, and gives first time
and general operating information.

Rack-mounting

Complete information for rack-mounting installation of the
Type R561B is given on the Rack-mounting fold-out pages at
the back of this manual.

Line Voltage

The Type R561B can be operated from either a 1 5-volt
or a 230-volt nominal line-voltage source. The Line Voltage
Selector assembly on the rear panel converts the instrument
from one operating range to the other. In addition, this
assembly changes the primary connections of the power
transformer to allow selection of one of three regulating
ranges. The assembly also includes two fuses to provide the
correct protection for the instrument; both fuses are connected
for 230-volt nominal operation, and only one fuse is
connected for 115-volt nominal operation. Use the following
procedure to obtain the proper line voltage and regulating
range settings of the Line Voltage Selector.

1. Disconnect the instrument from the power source.

2. Loosen the two captive screws which hold the cover
onto the voltage selector assembly; then pull to remove the
cover.

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

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

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

6. Before applying power to the instrument, check that
the indicating tabs on the switch bars are protruding through
the correct holes for the desired nominal line voltage and
regulating range.

TABLE 2-1

Regulating Ranges

Regulating Range,
Range Selector 115-Volts 230-Volt
Switch Position Nominal Nominal

LO (switch bar in 90 to 110 volts 180 to 220 volts

left holes)

M (switch bar in 104 to 126 volts 208 to 252 volts

middle holes)

HI (switch bar in 12 to 13 volts 224 to 272 volts

right holes)

Operating Temperature

The Type R561B can be operated where there ambient air

temperature is between 0°C and +50°C. The instrument can be

stored in ambient temperatures between -40°C and +65°C. After
storage at a temperature beyond the operating limits, allow the
chassis temperature to come within the operating limits before
power is applied.

A fan at the rear of the Type R561B provides forced air
cooling of the instrument. For proper circulation of air the
instrument should normally be operated with the top and bottom
covers in place. Do not block or restrict the air flow through the
instrument.

A thermal cutout provides thermal protection and disconnects
the power to the instrument if the internal temperature exceeds a
safe operating level. This device will automatically reapply power
when the temperature returns to a safe level.

Fig. 2-1. Line Voltage Selector assembly on the rear panel

(shown with cover removed).

CAUTION
Damage to the instrument may result from
incorrect Line Voltage Selector settings.

(A)

2-1A

Operating Instructions--Type R561B

SELECTION OF PLUG-IN UNITS

General Information

The Type R561B is designed to use Tektronix 2-series

and 3 series amplifier and time-base plug-in ’units for
amplifying the vertical input signal and producing the time­base sweep. The use of plug-in permits the selection of
display modes, bandwidth, sensitivity and number of inputs so
that the oscilloscope performance can be changed to meet
changing measurement needs.

NOTE
Programmable plug-in Types 3S6 and 3T6
are not compatible with the Type R561B.
However, the capability of these plug-ins
is available (without programmability)
with Types 3S5 and 3T5. Use the Type
3B5 in the right-hand (horizontal)
compartment only. Refer to the
instruction manual of the plug-in unit for
specific information.

To install a plug-in unit in the Type R561B, push it all the
way in to the plug-in compartment, then turn the locking knob
,at the bottom of the front panel) clockwise until it is tight. To
remove the unit, turn the knob counterclockwise until the latch
releases, then pull the unit out.

The accuracy of measurements made with the Type
R561B depends on the calibration of the plug-in units used.
Since the plug-in units drive the deflection plates directly, each
unit must be adjusted to match the deflection sensitivity of the
particular CRT that it drives. Therefore, the gain or sweep
timing adjustment must be checked each time a plug-in unit, is
changed. On most units, gain or timing calibration is made
with a front-panel screwdriver adjustment. (Sampling units
require special adjustment procedures.) Refer to the plug-in
unit instruction manual for the required procedure. Since the
various plug-in units present different output voltage levels to
the deflection plates, the FOCUS and ASTIGMATISM controls
will also require re-adjustment.

Plug-in units can be changed without turning off the
instrument power, but it is recommended that the power be
turned off while the change is made.

Either or both of the plug-in units can be operated on
special extension cables for troubleshooting. For normal
operation, power, the units must be installed in the
oscilloscope. If the instrument is operated with the plug-in
units on extension cables, the high-frequency response and
fast sweep rates will be affected.

Display Combinations

The plug-in unit in the left plug-in compartment controls
the vertical (Y-axis) deflection of the CRT beam, and the unit in
the right plug-in compartment controls the horizontal (X-axis)
deflection. The following paragraphs discuss some of the
display combinations that con be obtained.

Time-Base Displays. To produce a conventional time­base, or Y-T display, an amplifier plug-in unit is used in the
vertical (left) plug-in compartment and a time-base plug-in unit
is used in the horizontal (right) plug-in compartment.

If a vertical sweep is desired with the input signal
displayed horizontally, the time-base unit is inserted in the left
compartment

and the amplifier unit in the right compartment. However, if a
vertical sweep is used, there is no retrace blanking, no
chopped blanking multi-trace displays and the delaying-sweep
intensification does not operate because these circuits are
associated with the horizontal (right) plug-in compartment.

X-Y Displays. Two amplifier units may be used to
produce either a single or a multiple X-Y display (for example,
for phase comparison measurement). Plug-in units with
equal phase shift will produce an accurate X-Y display;
however, for high-frequency X-Y operation, use of two units of
the some type is recommended. Careful factory adjustment of
deflection-circuit capacitance to a standard value in the Type
R561B minimizes the high-frequency phase-shift between two
plug-in units of the same type. For multiple X-Y displays, both
synchronization and automatic pairings are provided for
some amplifier units. Refer to the instruction manual of the
plug-in unit to be used.

Multi-Trace Displays. The use of a dual-trace or multi­trace amplifier unit permits almost simultaneous viewing of two
or more signals. For a multi-trace amplifier unit with single
channel trigger capability ("Channel 1 Trigger"), the trigger
signal is applied through the Type R531B to the trigger circuit
in the time-base unit. This permits triggering from a single
input signal and the CRT display shows the time relationship
between the various signals. When using a plug-in without
single-channel triggering, an external trigger is recommended
to establish time relationship in multi-trace displays. In
chopped mode, the multi-trace blanking pulses from the
amplifier unit are applied internally through the Type R561 B to
the CRT cathode to blank the CRT beam while it is switched
from one channel to another (with the amplifier unit in the left
compartment and the time-base unit in the right compartment,
and with the rear panel CRT CATHODE SELECTOR switch in
the CHOPPED BLANKING position).

Delayed Sweep. A delayed-sweep time-base unit is
convenient for detailed viewing of pulse-train segments that
occur a relatively long time after the maximum-amplitude
(triggering) portion of the signal. The portion of the pulse train
to be displayed by the delayed sweep may be intensified on
the delaying-sweep display. A delayed-sweep unit that has a
calibrated time delay can also be used for making very
accurate (within 1%) time measurements

Raster Generation. A roster display can be presented by
using two time-base units, one in each compartment. Intensity
modulation can be achieved through the Z-axis of the CRT by
applying the signal to the EXT INPUT connector on the rear
panel and setting the CRT CATHODE SELECTOR to the EXT
INPUT position.

Sampling. The apparent bandwidth of the oscilloscope
can be increased to as much as one Gigahertz through the
use of sampling plug-in units. A sampling time-base unit must
be used with a sampling amplifier unit in the Type R561 B in
order to produce the sampling display (even for X-Y
operation). Generally, sampling and conventional plug-in units
cannot be used together in the oscilloscope. However, Type
3S1 and 3S2 sampling amplifiers do have limited compatibility
with conventional time-base units and the Type 3T5 sampling
time-base unit con generate a real-time staircase sweep
usable with conventional amplifiers.

Spectrum Analysis. Spectrum analyzer plug-in units
can be used in conjunction with conventional time-base units

2-2A (A)

Operating Instruction--Type R561 B

to produce a spectral display ( a graph of the relative
amplitude distribution as a function of frequency).

FUNCTIONS OF CONTROLS AND

CONNECTORS

A brief description of the function or operation of the front­and rear-panel controls and connectors follows. See Fig. 2-2
for locations.

Front Panel

ASTIGMATISM Used in conjunction with FOCUS

(Screwdriver control to obtain a well-defined display.

adjustment)
FOCUS Control Used to optimize focus.
INTENSITY Control Controls display brightness.
TRACE ALIGNMENT Permits alignment of the trace with

(Screwdriver respect to the horizontal graticule lines.

adjustment)
SCALE ILLUM Varies illumination of the graticule grid

Control lines.
POWER Switch Used to apply or remove instrument

input power.

POWER Indicator Lamp bulb which indicates that AC

power is applied to the instrument.

CALIBRATOR Switch Provides selection of one of several

values of square wave voltage or a
calibrated DC voltage. A calibrated DC
or square wave current can also be
selected.

CAL OUT Connector BNC connector at which calibrator

output voltage is available.

10 mA Current Loop Convenient means for calibrating

current probes.

Rear Panel

CRT CATHODE Permits .election of normal CRT
SELECTOR operation, chopped blanking (blanking

Switch of the between-channel switching

transients when using multi-channel
plug-in units in the chopped mode) and
external CRT cathode input (permitting
intensity modulation of the CRT by an
external signal).

EXT INPUT BNC connector by which an external signal

Connector can be applied to the CRT cathode.

Line Voltage Provides quick method of changing

Selector transformer taps to allow instrument to

operate over a wide range of line voltages.

Horizontal and Permit installation of auxiliary inputs

Vertical and outputs through rear panel.
Connector Holes

FIRST TIME OPERATION

The following procedure, using normal single-channel time­base mode, will demonstrate the basic operation of this instrument
and its plug-in units.

1. Install a 2-Series or 3-Series amplifier plug-in unit in the
vertical (left) plug-in compartment and a 2-Series or 3-Series time­base plug-in unit in the horizontal (right) plug-in compartment.
Lock the plug-in units in place with their locking screws.

2. Set the POWER switch to the off position (pushed in).

3. Connect the power cord from the Type R561B to the
proper line voltage.

NOTE
The LINE VOLTAGE SELECTOR assembly on
the rear panel should be checked to be sure
the Voltage Selector and Range Selector
switch bars are in the proper positions for
the line voltage applied.

4. Set the instrument controls as follows:

Type R561B

INTENSITY Counterclockwise
FOCUS Centered
SCALE ILLUM Counter-clockwise
ASTIGMATISM Centered
(Screwdriver adjustment)
CALIBRATOR 4 V
CRT CATHODE SELECTOR NORM

(rear panel)

Amplifier Unit

(For example: Type 3A6)

Position Centered
Mode Normal (Channel 1)
Volts/Div 2
Variable (Volts/Div) Calibrated
Input Coupling DC

Time-Base Unit

(For example: Type 3B3)

Position Centered
Time/Div .5 ms
Variable (Time/Div) Calibrated
Magnifier Off
Sweep Mode Normal

(A)

2-3A

Operating Instructions--Type R561 B

Fig. 2-2. Front-and rear-panel controls and connectors.

2-4A

(A)

Normal-Single Sweep Normal
Level Free run (clockwise)
Triggering Source Internal
Slope +
Coupling Auto

5. Connect a patch cord from the CAL OUT connector to

the Channel 1 input connector of the amplifier plug-in unit.

6. Set the POWER switch to ON (pulled out) and allow a

few minutes for warm up.

7. Adjust the INTENSITY control to obtain a display of
moderate brightness. The amplifier unit Position control may
have to be adjusted to position the free running trace on the
CRT screen. Do not turn the intensity higher than is
necessary for adequate observation of the display.

8. Trigger the display by adjusting the time-base Level
control.

9. Set the SCALE ILLUM control so the graticule
illumination is approximately equal to the intensity of the
display.

10. Adjust the time-base Position control to position the
start of the trace at the left edge of the graticule.

11. Adjust the FOCUS and ASTIGMATISM controls for a
sharp well-defined display over the entire trace length. (If a
focused display cannot be obtained, see Astigmatism
Adjustment later in this section under General Operating
Information.)

12. Adjust the TRACE ALIGNMENT screwdriver
adjustment to align the display with the graticule lines.

13. Check the gain and DC balance of the amplifier unit
and the timing adjustment (Sweep Cal) of the time-base unit
as given in the instruction manuals for those units before
making any voltage or time measurements. (In this
demonstration, the calibrator waveform should be displayed as
two divisions per cycle and two divisions in amplitude.)

GENERAL OPERATING INFORMATION

General

Refer to the amplifier unit manual for the following:
Compensation of probes, selection and use of input cables,
coupling and attenuation, and measurement of input signal
voltage and phase (X-Y). Refer to the time-are unit manual for
selection of triggering sources and coupling, and for
measurements of time intervals, frequency and phase (linear
measurement).

Scale Illumination

The CRT graticule is edge-lighted by three small lamps at
the bottom. The lighting can be adjusted to suit the ambient
light conditions by means of the SCALE ILLUM control.
Rotating the control clockwise increases the brightness of the
graticule scale markings.

Intensity Control

The setting of the INTENSITY control may affect the
correct focus of the display. Slight adjustment of the FOCUS
control may be necessary when the intensity level is changed.

(A)

Operating Instruction--Type R561B

Do not leave a bright, sharply focused spot on the CRT
screen for a prolonged period. An excessively bright stationary
spot may damage the CRT phosphor.

Astigmatism Adjustments

For most displays, the trace can be adequately focused using
only the front-panel FOCUS control. However, whenever a large
change is made in the beam intensity (to offset large changes in
sweep rates or triggering repetition rates), or when plug-in units
are changed, adjustment of the ASTIGMATISM control may also
be required for a sharp display.

To check for proper setting of the ASTIGMATISM adjustment,
slowly turn the FOCUS control through the optimum setting with a
signal displayed on the CRT screen. If the ASTIGMATISM
adjustment is correctly set, the vertical and horizontal portions of
the trace will come into sharpest focus at the same position of the
FOCUS control.

To set the ASTIGMATISM adjustment, use the following
procedure:

1. Connect a 4 V Calibrator signal to the vertical input and
set the corresponding Volts/Div switch to present 2.5 divisions of
vertical deflection.

2. Set the Time/Div switch .2 ms.

3. Adjust the INTENSITY control so that the rising portion of
the display can be seen.

4. Alternately adjust the FOCUS and ASTIGMATISM
controls so that the horizontal and vertical portions of the display
are equally focused.

Graticule

The graticule of the Type R561B is marked with eight vertical
and 10 horizontal divisions. Each division is one centimeter
square. In addition, each major division is divided into five minor
divisions on the center vertical and horizontal lines. With the
vertical gain and horizontal timing calibrated to the graticule,
accurate measurements can be made from the CRT. The
illumination of the graticule lines can be varied with the SCALE
ILLUM control.

Trace Alignment Adjustment

If a free-running trace is not parallel to the horizontal graticule
lines, set the TRACE ALIGNMENT adjustment as follows: position
the trace to the center horizontal line, and adjust the TRACE
ALIGNMENT adjustment so the trace is parallel with the horizontal
graticule lines.

1 kHz Calibrator

The 1 kHz Calibrator provides a convenient source of square
waves of known amplitude at an accurate frequency of one
kilohertz. The output square-wave voltages available at the CAL
OUT connector are 4 mV, 40 mV 0.4 V, 4 V and 40V. The loading
of a terminated 50Ω system at the CAL OUT connector will
provide output square-wave voltages of 2 mV, 20 mV and 0.2 V.
A constant 40-volt DC level is also provided.

2-5A

Operating Instructions--Type R561 B

The current link provides 10 milliamperes, available as
either DC or a square-wave current signal, which can be used
to check and calibrate current probe systems. This current
signal is obtained by clipping the probe around current loop.
The arrow indicates conventional current (i.e., positive to
negative).

Intensity (Z-Axis) Modulation

Intensity modulation can be used to relate other voltage
information to the display signal without changing the shape of
the waveform. The modulating signal is AC-coupled to the
CRT cathode through the rear-panel EXT INPUT connector
and the CRT CATHODE SELECTOR switch. With the
INTENSITY

control set correctly, a positive excursion will dim or blank the
CRT beam, and a negative excursion will brighten the beam
(see Section 1 for amplitudes).

Time markers may be applied for direct time reference of
the display or for establishing the sweep rate when
uncalibrated deflection is used. Fast-rise pulses of short
duration provide best resolution with respect to time. If the
markers are not time-related to the displayed wave-form, a
single sweep display is required. If sine waves are used for
Z-axis modulation, the minimum usable frequency is about
250 hertz, due to AC coupling at the input. Be sure the CRT
CATHODE SELECTOR is in the NORMAL position when the
EXT INPUT connector is not in use, to avoid random intensity
modulation from stray signals.

(A)

2-6A

SECTION 3

CIRCUIT DESCRIPTION

Introduction

The Tektronix Type RM561A Oscilloscope has a low­voltage power supply circuit, a cathode-ray tube circuit, and a
calibrator.

The low-voltage power supply circuit provides the
regulated and unregulated power used by the instrument and
the plug-in units.

The crt circuit has the necessary controls and input
facilities needed to give a sharp trace of useable intensity.

Two negative high-voltage power supply outputs are used
for the cathode, focus element, and control grid of the crt.

The calibrator produces amplitude-calibrated square
waves.

LOW-VOLTAGE POWER SUPPLY

The low-voltage power supply circuits have regulated
outputs of -100, -12.2, +125, and -300 volts, and unregulated
output of +420 volts. These circuits use silicon diode rectifiers
and series-regulators. Each regulator circuit has a vacuum
tube (or transistor, in the case of the -12.2-volt supply) in
series with the load. This tube’s series plate resistance (and
current) is controlled to maintain a constant voltage drop
across the load. For example, if the load increases the series
tube plate resistance decreases to pass more current to the
load. If the load decreases it passes less current. In both
cases, the voltage across the load remains the same.

The -100-, +125-, and +300-volt regulated supplies
require shunt resistors when supplying more current than can
be handled by the series tube. A shunt allows some of the
load current to bypass the supply-series-regulator tube. The
size of the shunt is very important. If the shunt resistance is
too high, the series tube can overheat; if the resistance is too
low, the supply can fail to regulate. If a plug-in draws an
amount of current that calls for a supply shunt, the correct
shunt resistance is located in that plug-in unit. When the unit
is plugged into the Type RM561A, the shunt is connected
around the series regulator tube. The plug-in portion of the
shunt is always in series with a resistor located in each power
supply circuit.

Power for the Type RM561A Oscilloscope and its plug-in
units is supplied through the power transformer T601. The two
primary windings of T601 are connected in parallel for 117-volt
operation, or in series for 234-volt operation, as shown on the
schematic diagram.

RM561A

The series tube plate resistance changes to hold the load voltage
constant. R616, -100 VOLTS adjustment, determines the
percentage of the total divider voltage applied to the grid of V634A
and thus controls the output voltage. When this control is properly
adjusted, the output is exactly -100 volts.

Should the output voltage tend to change because of a
change in input voltage or a change in load current, the potential
at the grid of V634A will change a proportional amount. Any
change at the grid of V634A is amplified by V634A and Q624 and
applied to the grid of V627. The resulting grid change at V627 will
cause its plate resistance to change in the direction needed to
bring the output back to --100 volts. C616 improves the response
of the regulator to sudden changes in output voltage R628 is part
of the series tube shunt. connected by some plug-in units.

+ 125-Volt Supply

The -100-volt supply serves as a reference for the +125 volt
supply. With the R651 end of the divider R650-R651 fixed at -100
volts, any change in the +125-volt output produces a proportional
change at the grid of V654. This change is amplified and supplied
to the grid of the series regulator tube, V667A. The change at the
grid of V667A changes its plate resistance to bring the output
voltage back to 4-125 volts. R656, the +125 VOLTS control,
determines the percentage of total divider voltage applied to the
grid of V654 and permits adjustment of the output voltage. W hen
this control is properly adjusted, the output is exactly +125 volts.
C650 improves the response of the regulator to sudden changes
in output voltage. .R666 is port of the series tube shunt.

+ 300-Volt Supply

The + 300-volt supply works the some as the + 125-volt
supply. To supply the voltage for the + 300-volt regulator, rectified
voltage from the transformer pins 21 and 22 is added to the
voltage supplying the + 125-volt regulator. R676, the -+ 300
VOLTS control, adjusts the output voltage. The + 300-volt supply
has an unregulated output of + 420-volts for the crt circuit.

- 12.2-Volt Supply

Operation of the --12.2-volt regulating circuit is essentially the
same as that of the other regulating circuits, except that
transistors are used instead of vacuum tubes. The base of Q734
is fixed near ---12 volts by the voltage divider R731-R732
between ---100 volts and ground. Any variation of the --12 2-volt
output at the emitter of Q734 is amplified by 0734 and 0744 to
change the collector resistance of 0757 which is in series with the
lead R730, the -12.2 VOLTS control, allows adjustment of the
voltage applied to the base, of Q734 and thus the output voltage.

- 100 Volt Supply

Reference voltage for the -100-volt supply is established
by the gas diode, V609. The constant voltage drop across
V609 establishes a fixed potential of about --85 volts at the
grid of V634B. Voltage at the grid of V634A is established by
the divider R616, R617, and R618. The difference in voltage
between the two grids of V634 determines the plate current cf
V634A. Plate current of V634A determines the base voltage
of transistor Q624 which in turn determines the grid voltage of
the series tube, V627.

(A)(A)

3-1

Circuit Description--Type RM561A

When this control is properly adjusted, the output is exactly -

12.2 volts. F720 protects Q757 in case of an overload on the -

-12.2-volt supply.

CRT CIRCUIT

The crt circuit contains the cathode-ray tube and two high­voltage supplies (one for the crt and focus element, the other
for the control grid). The circuit also contains the necessary
controls and signal input facilities.

Cathode-Ray Tube

A Tektronix T5032-31-1 ceramic-envelope cathode-ray
tube is used in the Type RM561A. The accelerating voltage is
approximately 3500 volts, developed by about -3300 volts at
the cathode and an average deflection plate voltage of about
+200 volts. With this accelerating voltage, the nominal vertical
and horizontal deflection factors are 19.5 and 18.4 volts per
centimeter respectively.

Deflection blanking of the crt beam is used in the Type
RM561A. The crt contains a special set of deflection plates,
pins 6 and 7, for this purpose. Both plates are connected to
+125 volts; however pin 6 is also driven by the horizontal plug­in unit.

During sweep time, or if no plug-in unit is installed, both
plates rest at +125 volts and permit the electron beam to pass
on to the crt phosphor. During sweep retrace, however, pin 6
is driven considerably away from +125 volts by the right-hand
plug-in unit. This scatters the beam and prevents it from being
displayed.

High-Voltage Supplies

Energy for both high-voltage supplies is furnished by
T801. V800, the primary of T801, and the stray circuit
capacitance form a Hartley oscillator which operates at about
45 kc.

The output of one secondary winding of T801, rectified by
V822, provides voltage for the crt cathode and focus element.
This voltage is about -3300 volts at the crt cathode, and
between about -2200 and -3000 volts at the focusing element,
depending on the setting of the FOCUS control. The 6.3-volt
crt heater is elevated to the cathode potential by R851.

The output of the other secondary winding of T801 is
rectified by V832 for the control grid. The grid voltage ranges
from -3200 to -3450 volts, depending on the setting of the
INTENSITY control. The reference to ground for this supply is
determined by the voltage at the junction of diodes D838 and
D839. The voltage at this junction, plus the setting of the
INTENSITY control, determines the crt bias and therefore the
intensity of the display.

Two neon bulbs, B856 and B857, keep the voltage
between the grid and cathode of the crt within safe limits. If
the voltage exceeds about 140 volts, the neons fire and the
voltage reduces to about 120 volts.

Regulation of the -3300-volt supply is accomplished through
feedback from the arm of R841. The -3450-volt supply is
regulated indirectly by mutual coupling in T801. If, because of
loading or a change in input voltage, the output of the -3300-volt
supply changes, a proportionate change occurs at the arm of
R841. This change is amplified by V814 and is coupled to the
screen of V800. The resulting change in screen voltage of V800
will increase or decrease the amplitude of oscillations in V800,
changing the output voltage of T801 in the direction needed to
return the high voltage to the correct level. The HIGH VOLTAGE
control, R841, permits adjustment of the output voltage by setting
the bias on V814B.

Deflection Signals

Push-pull signals for the deflection plates appear at pins 17
and 21 of the plug-in connector. The effective deflection circuit
capacitance these signals see at the connector affects the band­pass and phase shift of each plug-in unit. C760 and C761
(Interconnecting Socket diagram) are set at the factory.

Intensifying Signals

Two signals may be used to modulate the intensity of the crt
display. First, intensifying signals from a two-sweep (delaying­sweep) time-base plug-in unit are applied to the grid supply
through pin 14 of the right-hand Interconnecting Socket. W hen
the overall display intensity is reduced with the INTENSITY
control, positive intensifying pulses from a two-sweep time-base
plug-in unit will brighten any desired portion of the display.

The ground return for the crt grid supply can be either through
D838 in the case where the plug-in unit does not supply
intensifying signals or through D839 to a negative voltage in the
intensifying circuit of the plug-in unit. In the second case D838 is
back-biased and the junction of D838 and D839 is at a low
negative voltage. With the same setting of the INTENSITY
control, the first case will provide a brighter display. The second
case provides a slightly dimmer display due to the plug-in unit
negative voltage. Intensification results when the plug-in unit
positive pulse turns D839 off and the crt grid supply return again
becomes D838. R837 and C837 then couple the leading edge of
the intensifying pulse directly to the crt grid.

Other external intensifying signals can be fed to the crt
cathode through the EXT CRT CATHODE jack. Depending on the
setting of the INTENSITY control, a negative pulse of 5 volts or
more will turn the crt beam on.

Crt Controls

The INTENSITY control, R833, has a range of about 250 volts
to control the crt bias and permit changing the intensity of the
display.

The FOCUS control, R844, adjusts the focus of the crt by
varying the voltage at the focusing anode through a range from
about -2200 to -3000 volts.

The ASTIG. control, R864, has a 300-volt adjustment range.

3-2 (A)(A)

Circuit Description--Type RM561A

The GEOMETRY control, R865, adjusts the geometry by
varying the voltage of the crt isolation shield through a range
from +180 to +246 volts.

The TRACE ALIGNMENT control, R860, rotates the
display so it can be aligned with the graticule.

CALIBRATOR

The calibrator for the Type RM561A Oscilloscope
produces line-frequency amplitude-calibrated square waves.
The 6.3-volt (approximately 18 volts peak-to-peak) ac heater
voltage for V884 is supplied through C876 to the cathode of
V884A. The signal at the plate of V884A is coupled to the grid
of V884B to turn that tube on and off.

(A)(A)

Regenerative feedback from the plate of V884B to the grid of
V884A speeds up the switching action, and drives V884A into and
out of cutoff.

The voltage present at the cathode of V884B during the time
that V884B is conducting is adjusted to exactly 100 volts with the
CAL. AMPL. adjustment, R871.

The voltage divider in the cathode circuit of V884B contains
precision resistors to provide an output accuracy of 3% or better
at the various settings of the CALIBRATOR control.

When the CALIBRATOR control is set to the IV position, there
will be a 0.1-volt output when the CAL. OUT connector is
terminated in 50 ohms.

3-3

SECTION 3A

CIRCUIT DESCRIPTION

Type R561B

R561B

Introduction

This section of the manual contains a description of the
circuitry used in the Type R561B Oscilloscope. Each circuit is
described in detail using a detailed block diagram to show the
interconnections between the stages in each major circuit and
the relationship of the front-panel controls to the individual
stages. Complete schematic diagrams are located at the rear
of this manual.

LOW-VOLTAGE POWER SUPPLY

General

The Low-Voltage Power Supply circuit provides the
operating power for this instrument from four regulated
supplies. Electronic regulation is used -to provide stable, low­ripple output voltages. Each regulated supply contains a short
protection circuit to prevent instrument damage if a supply is
inadvertently shorted to ground or to another supply. The
voltage input stage includes the Voltage Selector Assembly
which allows selection of the nominal operating voltage and
regulating range for the instrument. Fig. 3-1 shows a detailed
block diagram of the Low-Voltage Power Supply.

Power Input

Power is applied to the primary of transformer T1 through
fuse F1, POWER switch SW1, thermal cutout TK1, Voltage
Selector switch SW2 and Range Selector switch SW3. SW2
connects the split primaries of T1 in parallel for 115-volt
nominal operation, or in series for 230-volt nominal operation.
SW3 allows three ranges of regulation by changing the taps
on the primary windings to fit different line requirements. A
second fuse, F2, is connected into the circuit when SW2 is set
to the 230V position to provide the correct protection for 230­volt operation.

Thermal cutout TK1 provides thermal protection by
interrupting the power if the instrument overheats. When the
temperature returns to a safe level, TK1 automatically closes
to re-apply the power.

- 100 Volt Supply

The -100-Volt Supply provides the reference voltage for
the remaining supplies. The output from the secondary of T1
is rectified by bridge rectifier D8A-D. This voltage is filtered by
C9, then applied to the -100-Volt Series Regulator stage to
provide a stable output voltage. The Series Regulator can be
compared to a variable resistance which is changed to
stabilize the output voltage. The conductance

of the Series Regulator stage is controlled by the Error Amplifier to
provide the correct regulated output voltage.

The Error Amplifier consists of Q12 and Q14, which are
connected as a comparator. The output at the collector of Q14
indicates any voltage variations which occur at the base of Q14
relative to the fixed voltage at the base of Q12. Zener diode D10
maintains a fixed 9-volt drop, setting the base of Q12 at about -9
volts. The base level of Q14 is determined by the voltage divider
network R18-R19-R20-R21-R23. R23, the -100 Volts adjustment,
allows the operating point of the Error Amplifier to be adjusted to
set the output voltage of the supply at -100 volts. R13 is the
emitter resistor for both comparator transistors and the current
through it divides between Q12 and Q14. The output current of
the Error Amplifier stage controls the conduction of the Series
Regulator stage. This is accomplished as follows: Assume that
the output voltage increases (becomes more negative) because of
a change in load or an increase in line voltage. This negative­going voltage change at the output is applied to the base of Q14,
reducing the conduction of Q14. As current through Q14 is
reduced, Q24 base current increases. This results in increased
Q24 collector current, increasing the voltage drop across R25 and
R26 and pulling the base of Q28 negative. The emitter of Q28
follows the base; hence, the base of Q32 is also pulled negative.
Reduced current through Series Regulator Q32 decreases current
through the load, causing the output voltage to decrease (become
less negative) to its correct level. These changes occur rapidly,
and the effect is to maintain unchanged output voltage. In a
similar manner, the Series Regulator and Error Amplifier stages
compensate for output changes due to ripple. As will be seen in
subsequent paragraphs, R33 determines the limit current for the
Series Regulator stage, and thus for the load. Transients beyond
the frequency range of the regulator are filtered by C31 to prevent
their appearance on the output voltage.

When the power switch is activated, diode D25 provides a
base current path for Q28, allowing the -100-Volt Supply to turn on
first, since all the other supplies are dependent upon its output.
As the -100-Volt Supply output builds up to its correct level, D25 is
reverse biased and remains off during normal operation of the
instrument.

The Short-Protection Amplifier stage, Q30, protects the -100­Volt Supply if the output is shorted, and also serves to limit the
current demanded from the Series Regulator under excessive
load. During normal operation, divider R30-R31 sets the base of
Q30 to a point below the turn-on level of the transistor. When
excess current is demanded from Series Regulator Q32 due to an
overload or short circuit, the additional current through R33 raises
the emitter of Q32 more positive. This produces a
corresponding change at the base of Q32, which is connected
through R30

(A)

3-1A

Circuit Description--Type R561B

Fig. 3-1. Power Supply detailed block diagram.

3-2A

(A)

Circuit Description--Type R561B

to the base of Q30. This positive-going change biases Q30
into conduction. As a result, less current is available to Q28,
to Q32 and to the load, thus causing the supply to lose
regulation. R31 senses the decrease in load voltage and adds
to increasing base current of Q30. As the collector of Q30
goes negative, conduction of Q28 and Q32 is further
decreased. Thus the output current is decreased and remains
low until the excessive load is removed. D19, together with
divider R18-R19-R20, provides protection to the --12.2-Volt
supply in the event the -100-Volt Supply is shorted to the -

12.2-Volt Supply by causing the -100-Volt Supply to lose
regulation, and therefore lose reference voltage for the -12.2­Volt Supply. D31 protects the -100-Volt Supply from
damaging polarity reversal if it is shorted to either the +125­Volt Supply or the +300-Volt Supply.

- 12.2-Volt Supply

Rectified voltage for operation of the -12.2-Volt Supply is
provided by D35A-B, filtered by C36 and applied to the -12.2­Volt Supply Series Regulator stage. Reference voltage for this
supply is provided by voltage divider R42-R43 between the
regulated -100-Volt Supply and ground. If the -12.2-volt output
changes, a sample of the change appears at the base of Q46
as an error signal. Regulation of the output voltage is
controlled by Error Amplifier Q44-Q46-Q49 and Series
Regulator Q51 in a manner similar to that described for the ­100-Volt Supply. Transients beyond the frequency range of
the regulator are filtered by C47.

Short protection is provided by Q38 and R38. For normal
operation, the emitter-base voltage of Q38 is not enough to
bias it into conduction. However, when the output is shorted,
the high current demanded from the -12.2-Volt Supply is
drown through R38, producing a voltage drop sufficient to
forward bias Q38. Q38 collector current then produces an
increased voltage drop across R40, reducing the conduction of
both Q49 and Q51 to limit the output current. R39 protects
Q38 from sudden current surges by limiting the base current.
D47 protects the -12.2-Volt Supply from damage if it is shorted
to either the +;125-Volt Supply or the +300-Volt Supply.

+ 125-Volt Supply

Rectified voltage for operation of the +125-Volt Supply is
provided by D53A-D, filtered by C54 and applied to the +125­Volt Supply Series Regulator stage. The +125-volt output is
summed with the -100-volt reference through divider R62-R63,
and the summation is applied through R61 to the base of Q60
and compared to the grounded base of Q58. If the +125-volt
output changes, a sample of the change appears at the base
of Q60 as an error signal. Regulation of the output voltage is
controlled by Error Amplifier Q58-Q60-Q66-Q68 and Series
Regulator Q74 in a manner similar to that described for the ­100-Volt Supply. Transients beyond the frequency range of
the regulator are filtered by C97B-C to prevent their
appearance on the output voltage.

Short protection for this supply is provided by the Short­Protection amplifier stage, Q70, which functions in a manner
similar to that described for Q30 in the --10Volt Supply. D62
protects the Error Amplifier from damage if the output of the
+125-Volt Supply collapses or goes negative, causing C62 to

rapidly discharge and reverse bias 060. Diode D75 protects
electrolytic capacitor C97B-C and the transistors in the circuit from
damaging polarity reversals in the event the +300-volt output is
shored to ground or to one of the negative supplies. D76 causes
the +125-Volt Supply to go into current limiting when the +300-Volt
Supply is shorted to ground or to one of the negative supplies.

+ 300-Volt Supply

Rectified voltage for operation of the +300-Volt Supply is
provided by D77A-D, filtered by C78 and applied from the
negative side of the rectifier to the +300-Volt Supply Series
Regulator stage. The +300-volt output is summed with the -100­volt reference through divider R80-R81, and the summation is
applied through R83 to base of Q84 and compared to the
grounded base of Q86. If the +300-volt output changes, a
sample of the change appears at the base of Q84 as an error
signal. Regulation of the output voltage is controlled by Error
Amplifier Q84-Q86-Q88-Q90 and Series Regulator Q96 in a
manner similar to that described for the -100-Volt Supply.
Transients beyond the frequency range of the regulator are filtered
by C97A. The load current through Series Regulator Q96 also
posses through the +125-Volt Supply Series Regulator, Q74.
However, this does not affect the limit current of the +125-Volt
Supply.

Shorting protection for this supply is provided by the Short­Protection Amplifier stage, Q91, which functions in a manner
similar to that described for Q30 in the -100-Volt Supply. D80
protects the Error Amplifier from damage if the output of the +300­Volt Supply collapses or goes negative, and D95 protects the
transistors in the circuit from damaging polarity reversals in the
event the +125-Volt Supply is shorted to ground or to one of the
negative supplies.

6.5-Volt RMS AC Source

The four 6.5-volt RMS secondary windings of T1 provide
power for the CRT heater, the plug-in heaters via J11 and J21, the
pilot light, B7, and the scale illumination lights, B4, B5, and B6.
Current through the scale illumination lights is controlled by the
SCALE ILLUM control, R4, to change the brightness of the
graticule lines.

DEFLECTION CIRCUITS

horizontal and vertical signals for deflecting the CRT beam are
received through pins 17 and 21 of each plug-in unit and applied
to the respective deflection plates of the CRT. The effective
deflection circuit capacitance encountered by each of these
signals at the plug-in connector affects the bandwidth and phase
shift of the plug-in unit. Compensating capacitors C102 and C109
(shown on the Plug-In Connectors diagram) are factory-adjusted
to set the effective capacitance at a standard value of 14.3
picofarads to ensure plug-in compatibility.

1 kHz CALIBRATOR

General

The 1 kHz Calibrator circuit produces a square-wave output
with accurate amplitude and frequency. This output is available
as a square-wave voltage at the CAL OUT connector or as a
square-wave current through the 10 mA probe current

(A)

3-3A

Circuit Description--Type R561B

Fig. 3-2. 1 kHz Calibrator detailed block diagram.

loop. An accurate +40 volts DC level is also available. The
CALIBRATOR switch selects the attenuation of the output
signal to provide square-wave voltage outputs between 40
volts and 4 millivolts (between 0.2 volts and 2 millivolts into 50
ohms) peak to peak. Fig. 3-2 shows a detailed block diagram
of the 1 kHz Calibrator circuit.

Calibrator Multivibrator

The Calibrator Multivibrator is comprised of Q151 and
Q159, and is a free-running emitter-coupled multivibrator. The
circuit operates in a symmetrical manner and the output is an
accurate one-kilohertz square wave. Only an approximate 9­volt change is exhibited at the emitters of Q151 and Q159, so
that an essentially constant current of about 0.8 mA is
maintained through resistors R150 and R1 58.

Refer to the wave shapes shown in Fig. 3-3 for this
discussion. With the CALIBRATOR switch, SW150, in all
positions except 1 mA DC and OFF, the emitters of Q151 and
Q159 are returned to the +125-volt supply through D151-R150
and D159-R158. Assume that the multivibrator has just
switched states; Q151 is off and Q159 is on. This is To in Fig.
3-3. The base potential of Q159 is set to about -11.0 volts by
voltage divider R153-R154-R156 to ensure that Q159 will not
saturate. The voltage at the anode of D159 is about -9.8 volts
because of the voltage drop across two forward biased
junctions. Capacitor C157 had about a 2-volt charge as
switching occurred; thus, the voltage at the anode of D151 is
about -7.8 volts, cutting off Q151. C157 begins to charge
toward the +125-volt supply via R150. Total current through
Q159 is about 1.6 mA; 0.8 mA through R158 and 0.8 mA
through C157 and R150.

After about 0.5 milliseconds (corresponding with T, in Fig.
3-3), C157 has charged to the turn-on level of Q151 and D151.
At this point, the capacitor has a charge of about 11 volts and
the potential at the anode of D151 is about +1.2 volts. The
capacitor charging current through Q159 ceases as Q151 and
D151 begin

to conduct. As the collector of Q151 (hence the base of Q159)
rises, Q159 and D159 are switched off and C157 begins to
discharge through R158. The C157-R158 current sums with R150
current through Q151, producing an approximate 9-volt positive­going step at the base of Q159.

C157 continues to discharge, and after 0.5 milliseconds (T,
in Fig. 3-3), the voltage at the anode of D159 has risen to
forward-bias Q159 and D159. As Q159 begins to conduct, the
anode of D159 is clamped at about 0.8 volts and discharge action
of C157 is halted. The current through Q151 decreases, causing
its collector to introduce a negative-going step, which is connected
through the Q159 base-emitter junction and D159 to C157.
Because C157 cannot obtain an instantaneous charge, the anode
of D151 is pulled negative to reverse bias D151 and Q151. Q151
turns off, and its collector falls rapidly to about -11.0 volts,
resulting in an approximate 9-volt negative-going step applied
through Q159 and D159 to C157. The anode of D151 is pulled
down to about -7.8 volts, completing the cycle.

The Calibrator Multivibrator circuit has been designed to
repeat the preceding sequence at an accurate one-kilohertz
frequency. However, since a tolerance range of the passive
components does exist, the frequency can be adjusted by varying
slightly the amplitude across C157 during the charge-discharge
cycle. This is accomplished by adjustment of R154, Frequency,
which determines the potential on D159 anode at the instant the
diode turns on. For example, with greater amplitude, longer
charge and discharge times are required, thus lowering the
frequency.

Output Stage

The output stage consists of the Current Switch, Q162, and
the Divider Network. During the half cycle that Q159 is
conducting, current is injected into the base of Q162. Q162
saturates and its collector drops to about -12 volts, reverse
biasing D168. With D18 off, there is no current through R170 and
R171, and the output level at the cathode of D168 drops to zero
volts.

(A)

3-4A

When Q159 turns off, Q162 turns off and D161 turns on to
protect the Q162 base-emitter junction from reverse-bias
breakdown. D164 and D168 turn on, and the output of the
circuit (at D168 cathode) is dependent upon voltage divider
R166-R167-R170-R171 between +125 volts and ground. This
output level is set to exactly +40 volts by adjustment of R166,
Amplitude. When this adjustment is made, the current through
the divider is an accurate 10 mA, which is available at the
current probe loop in the 10 mA positions of the CALIBRATOR
switch.

The signal voltage available at the CAL OUT connector is
determined by the divider network (made up of precision
resistors) and the setting of the CALIBRATOR switch. In the
10 mA DC (40 VDC) position, the Calibrator Multivibrator is
inoperative so that a +40-volt DC output level is produced.
R173 is placed in series with the R166-R167-R170-R171
resistance to obtain an effective resistance of 450 ohms with 4
volts applied, as seen by the CAL OUT connector in the 4 V
position of the switch. This effective resistance becomes port
of the output voltage divider in the positions of 0.4 V and below
(these positions have an accurate 50- ohm output resistance,
which when terminated by 50 ohms can further divide the
outputs by two, providing outputs of 0.2V, 20 mV and 2 mV).
In the 10 mA position, the CAL OUT connector is grounded.

R183, which is about ten times the resistance of the braid
of a 42-inch coaxial cable, cancels any ground loop current
that may exist between the CAL OUT connector and some
other instrument chassis.

CRT CIRCUIT
General

The CRT Circuit provides the high voltage and control
circuits necessary for operation of the cathode-ray tube (CRT).
Fig. 3-4 shows a detailed block diagram of the CRT Circuit.

High Voltage Oscillator

Q219 and its associated circuitry comprise a class C
oscillator to provide the drive for the high-voltage transformer,
T220. When the instrument is turned on, conduction of Q214
provides a base current path for Q219. The collector current
of Q219 increases and a voltage is developed across the
collector winding of T220. This produces a corresponding
voltage increase in the feedback winding of T220 which is
connected to the base of Q219, causing it to conduct harder.
While Q219 is conducting, C217 charges negatively to the
peak to peak voltage of the feed-back winding. Eventually the
rate of collector current increase in Q219 becomes less than
that required to maintain the voltage across the collector
winding and the voltage drops.This turns off Q219 by way of
feedback voltage to the base. During the interval that Q219 is
not conducting, the negative charge on C217 is partially
removed through Q214. Q219 remains off until the feedback
voltage on the base is near the peak positive value again. The
cycle repeats at a frequency of 40 to 50 kilohertz. The
amplitude of sustained oscillation depends upon the average
current delivered to the base of Q219, and finally, the average
Q219 collector current.

Circuit Description--Typo R561 B

Fig. 3-3. Calibrator Multivibrator waveforms.

High Voltage Regulator

Feedback from the secondary of T220 and +125 volts is
summed through the voltage divider network consisting of R200,
R201, R206, R208 and R233 through R238, and the difference is
applied to the gate of Field-Effect Transistor Q211.. This sample
of the output voltage is compared to the regulated --12.2-volt level
at the source of Q211. It is then inverted and amplified by Q211
and applied to the base of Q214. Amplitude of the oscillations at
the collector of Q219 is determined by the average collector
current of Q214.

Regulation. is accomplished as follows: If the output voltage
at the -330Q V test point starts to go positive (becomes less
negative), a sample of this positive-going voltage is applied to the
gate of Q211. Conduction of Q211 is increased, and as its drain
goes negative because of the voltage dropped across R211, the
base current of Q214 is increased. An increase in conduction of
Q214 increases the average collector current, which is applied
through the feedback winding of T220 to the base of Q219. Q219
conducts harder, increasing the collector current to produce a
larger induced voltage in the secondary of T220. This increased
voltage appears as more negative voltage at the -3300 V test
point to correct the original positive-going change. By sampling
the output from the cathode supply in this manner, the total output
of the high-voltage supply is held constant.

(A)

3-5A

Circuit Description--Type R561B

Fig. 3-4. CRT Circuit detailed block diagram.

Output voltage level of the high-voltage supply is controlled by
the High Voltage adjustment, R206, in the gate circuit of Q211.
This adjustment sets the effective divider ratio, which in turn
determines the voltage necessary to satisfy the quiescent
condition of Q214 and Q219 in the manner described for a
change in output voltage. Neon bulb B209 and diode D212
protect the FET, Q211, from damage due to excessive voltage.

High Voltage Rectifiers and Output

The high-voltage transformer, T220, has two output
windings. These windings provide the negative CRT cathode
potential and the CRT control grid bias.

The accelerating potential for the CRT cathode is supplied
by the half-wave rectifier D221 and held constant by the High­Voltage Regulator stage in the primary of T220. The output
level is adjustable to about -3300 volts on the cathode by the
High Voltage adjustment mentioned previously. (The 6.5-volt
CRT cathode heater is also elevated to the cathode potential
through R246.)

Half-wave rectifier D260 provides a negative voltage for
the control grid. The voltage applied to-the-control-grid is
determined by the setting of the INTENSITY control (to be

(A)

3-6A

Circuit Description--Type R561B

discussed in the next paragraph), the CRT Grid Bias control
(R269) and any intensification signals received from the time­base plug-in unit (delayed sweep and sampling units only).
Reference to ground for this supply is set by the conduction of
D272.

Beam current is controlled by R225, INTENSITY. As the
control is rotated clockwise, the wiper arm moves toward -100
volts. This more negative DC reference voltage is applied to
the secondary winding controlling the CRT cathode, reducing
the voltage demanded of the winding to maintain -3300 volts at
the -3300 V test point. This is accomplished by the regulator
circuit. The voltage across the grid winding is also reduced,
which results in a more positive voltage applied to the CRT
control grid, thus increasing beam current. Beam current is
reduced in a like manner by rotating R225 counterclockwise.

Neon bulbs B277, B278 and B279 provide protection to
the CRT if the voltage difference between the control grid and
the cathode exceeds about 135 volts.

CRT Control Circuits

In addition to the INTENSITY control discussed
previously, the FOCUS and ASTIGMATISM controls have
been incorporated for arriving at the optimum CRT display.
FOCUS control R237 provides the correct voltage for the
second anode in the CRT. Proper voltage for the third anode
is obtained by adjusting ASTIGMATISM control R257. In order
to obtain optimum spot size and shape, both the FOCUS and
ASTIGMATISM controls are adjusted to provide the proper
electrostatic lens configuration in the CRT. The TRACE
ALIGNMENT control, R259, permits adjustment of the DC
current through beam-rotation coil L259 to align the display
with the horizontal graticule lines. The Geometry adjustment,
R256, controls the overall geometry of the display.

Blanking

The CRT beam is blanked by a special set of deflection
plates in the CRT. One of the plates (pin 7) is connected
directly to the +-125-volt supply. The second plate (pin 6) is
connected through plug-in connector J21 to the horizontal
plug-in unit. When there is no sweep, a quiescent voltage is

applied from the horizontal unit to create a difference of potential
between the two plates. This voltage can either be positive or
negative with respect to the +125 volts on the other plate. The
potential difference created is sufficient to deflect the CRT beam
so that it is absorbed in the deflection structure and does not
reach the screen.

The CRT beam is unblanked whenever the two deflection
plate voltages become equal. For example, if a sweep occurs or if
the horizontal plug-in unit is removed, the voltages are made
equal and the beam is allowed to pass through to the CRT screen.
Sweep unblanking is produced by either a positive or negative
gate pulse (depending on the quiescent level) applied to pin 6,
equaling the +125 volts normally present at pin 7. In a like
manner, when the horizontal plug-in unit is removed, the two
deflection plates are equalized through R244 at +125 volts.

Intensity Modulation

The intensity of the CRT display may be modulated by
applying signals to either the grid or the cathode of the CRT.

Intensifying signals from a delayed sweep time-base plug-in
unit are applied to the grid supply via pin 14 of the horizontal plug­in interconnecting socket, J21. These signals brighten the
delayed-sweep portion of the delaying-sweep display. When the
time-base unit is set to Intensified, the control grid supply is
referred to a negative voltage in the intensifying circuit through
D275, reducing the overall display intensity. At this time, D272 is
reverse biased by the negative voltage at the juncture of the two
diodes. Intensification results when the positive-going pulse from
the time-base unit reverse biases D275 and the grid supply is
referred to ground through D272 (as for normal operation). The
positive-going pulse is then coupled through R275 and C275 to
the CRT control grid. Thus the brightened portion of the display is
the same intensity as a normal display and the background trace
is dimmed.

External modulating signals may also be applied to the CRT
by way of the cathode, through the rear-panel EXT INPUT
connector, J255, and the CRT CATHODE SELECTOR, SW255.
With the INTENSITY control adjusted properly, a positive or
negative pulse between 3 and 50 volts in amplitude will produce
dimming or intensification of the CRT beam.

When a multi-channel vertical plug-in amplifier that provides
dual-trace chopped blanking pulses is used, the blanking pulses
are applied via the interconnecting socket J11 and the CRT
CATHODE SELECTOR to the CRT cathode circuit. These pulses
are about 5 volts in amplitude, and at normal intensity levels are
sufficient to cut off the CRT beam during the time the amplifier
channels in the vertical plug-in unit are being switched.

(A)

3-7A

SECTION 4

MAINTENANCE

R561A

PREVENTIVE MAINTENANCE

Cleaning

Occasionally blow the dust out of the instrument with a
low-velocity dry air stream. Remove persistent dirt with a
small paint brush or damp cloth. The screen on the fan con be
snapped out and should be cleaned as needed. Check it
frequently.

Fan Oiling

The fan should be oiled with a few drops of oil about every
six months. An industrial hypodermic syringe and needle is
used to insert oil through a protective rubber cap located under
the fan label. The oil recommended is Anderol L826 from the
Lehigh Company or Rotron distributors, but if not available, a
good light machine oil may be used. If a syringe and needle
cannot be obtained locally, you can order them through the
NICP by specifying Hypodermic Syringe, Tektronix Part No.
003-282 and Hypodermic Needle, Tektronix Part No. 003-285.

Fig. 4-1 shows how to oil the fan. Place the needle at the
point on the label shown in Fig. 4-1. With the needle at about
45’, pierce the label and rubber cap (located under the label);
insert the needle about 1/4" and depress the syringe-plunger
to inject a few drops of oil.

CORRECTIVE MAINTENANCE

Replacing Parts

Most parts in the Type RM561A Oscilloscope can be replaced
without detailed instructions. Some parts, however, should be
replaced by using definite procedures. These procedures are
described in the following paragraphs.

A replaced part may affect instrument calibration. Check and
adjust where needed.

Soldering Precautions and Procedure

In Tektronix instruments, parts are connected to ceramic
terminal strip notches with solder containing about 3% silver.
The bond between the notch and ceramic strip may be broken by
repeated use of ordinary 60 40 tin-lead solder or by excessive
heat. Therefore, when resoldering parts to a ceramic strip use
solder containing 3% silver and do not overheat the work.
Occasional use of ordinary solder, however, will not break the
bond. Usually 3% silver solder is available locally; or one-pound
rolls may be ordered from the NICP.

The following soldering procedure may be used to remove
and replace parts on a ceramic terminal strip.

1. Use 50-to-70-watt soldering iron with a wedge shaped
tip. (With this type tip you can heat the solder slot without
overheating the strip.)

2. Tin the soldering iron tip with silver-bearing solder.

3. Heat the parts soldered to the ceramic strip only
enough to make the solder flow freely. Do this by touching one
corner of the soldering iron tip to the notch. (Be careful: excessive
pressure will break the ceramic strip.)

4. When you remove a part, pull its lead out of the notch
while the solder is hot.

5. When you replace a part use only enough solder to cover
the wires and form a small fillet in the notch.

6. Clip excess leads of parts replaced and be sure to
remove all clippings from the instrument.

Fig. 4-1. Fan motor oiling with hypodermic

(A)(A)

Replacing Ceramic Terminal Strips

Damaged ceramic terminal strips can be replaced by the
following procedure. Fig. 4-2 shows how ceramic strip parts are
assembled.

1. Unsolder all connections to damaged ceramic strip.

2. Cut off one side of each plastic yoke holding the old

ceramic strip.

3. Remove old ceramic strip.

4. Remove remainder of old yokes from spacers.

4-1

Maintenance--Type RM561A

Fig. 4-2. Ceramic terminal strip assembly.

5. Replace old spacers with new ones. (If not damaged,

spacers can be reused.)

6. Set new ceramic strip yoke pins into spacers.

7. Drive new yoke pins completely into spacers by
pressing or lightly tapping the ceramic strip directly above the
yokes. Be careful, don’t break strips.

8. Cut off portion of new yoke pins protruding through
spacers on side of chassis opposite the ceramic strip.

9. Resolder connections to new ceramic strip using the
information headed Soldering Precautions and Procedure.

Replacing Calibrator Switch

The entire switch should be replaced and can be ordered

either wired or unwired.

falls directly under the grounding strip. Tighten the base clamp
screw.

After the crt is replaced, it may be necessary to adjust the
TRACE ALIGNMENT and HIGH VOLTAGE controls and the
deflection-circuit capacitance (C760 and C761) according to the
calibration procedure. Also check the calibration of time-base and
amplifier plug-in units.

Cathode-Ray Tube

WARNING
When replacing crt, wear a plastic face
mask and protective gloves for protection
in case tube implodes.

To remove the cathode-ray tube, disconnect the four
leads connected to the neck of the tube, the tube socket, and
loosen the tube clump on tube base. Remove the crt bezel,
light reflector and light shield. Pull the crt straight out
through the front panel, being careful not to bend or break the
crt neck pins. The rubber gasket and implosion shield can be
removed from the crt face after it is out of the instrument.

Install the new crt by the reverse of the preceding
procedure. When replacing the implosion shield be sure that
the notched side is down. Follow the color-code information
on the tube shield when the crt neck pin leads are replaced.
When the crt is properly installed, the back of its faceplate is
flush with the instrument front panel.

Correct position of the shield extension, grounding strip
and Mylar sleeve is important when re-installing the crt.
Replace these components on the positions shown in Fig. 4-

3. Note that the gap between the ends of the shield extension

Fig. 4-3. Correct position of shield extension and Mylar sleeve.

TROUBLESHOOTING

If trouble occurs in the Type RM561A Oscilloscope, a five­step procedure may be used for repair. First, confirm the trouble.
Next, isolate trouble to a plug-in unit or to the Type RM561A.
Localize a trouble in the Type RM561A to the Power Supply, Crt
Circuit, or Calibrator. Troubleshoot the correct circuit to find the
defective parts. Replace defective parts.

Confirmation of Trouble

Improper control settings may at times give indications of
trouble. Therefore, you should be sure that the apparent trouble is
not caused by improper front panel control settings. For example,
an improper setting of the SOURCE or COUPLING switch on a
time-base unit can cause apparent trigging troubles: an improper
setting of the VARIABLE

(A)(A)

4-2