Tektronix 7B92 User manual

Tektronix, Inc.
P.O. Box
500
Beaverton, Oregon 97005
SCIJn!~ bv OUI .fOUr Ce -Oplion .f =>
TEKTRONI»
7892
DUAL TIME IlASE
SERVICE
INSTRUCTION MANUAL
Serial Number
373

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WARRANTY
All TEKTRONIX instruments are w ..... anted lIIJIIinst
defective matlfial , workmanship for one year . Any
';:'K~:i: :~ the warranty should b. taken up
T Field Engin.e, or representative.
Copyr ight @ 1973 by T ektr onix , In c., Beaver to n, Oregon .
Printed in the United State s of Am erica. All fights reserved.
Contents of this publica ti on may not be reproduced in any
form wit hout pe rmi ssio n of Tektronix, In c.
U.S.A. and Foreign TEKTRONIX products covered by U .S.
and f ore ign patents and lo r patents pending.
TEKTRONIX is a reoistered t,adematk of T aktro ni )!;, Inc.

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7B92 Service
TABLE OF CONTENTS
SECTION 1 OPERATING INFORMATION
Preliminary Information
Installation
Controls and Connectors
General
Main Triggering Controls
Sweep Controls
Delayed Triggering Controls
Front-Panel Inputs
SECTION 2 CIRCUIT DESCRIPTION
Block Diagram Description
SECTION 3 MAINTENANCE
Preventive Maintenance
General
Cleaning
Visual Inspection
SemiconductorChecks
Recalibration
Troubleshooting
Introduction
"-
Troubleshooting Aids
Troubleshooting Equipment
Troubleshooting Techniques
Corrective Maintenance
General
Obtaining Replacement Parts
Component Replacement
SECTION 4 CALIBRATION
Calibration Interval
Tektronix Field Service
l
®
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Page
1-1
1-1
1-1
1-1
1-1
1-4
1-5
1-5
2-1
3-1
3-1
3-1
3-1
3-1
3-1
3-1
3-1
3-2
3-2
3-3
3-4
3-4
3-4
3-4
Using This Procedure
General
Index
Performance Check
Partial Calibration
Complete Calibration Procedure
Test Equipment Required
General
Special Calibration Fixtures
Calibration Equipment
Alternatives
Test Equipment
Calibration Procedure
Introduction
Index to Calibration Procedure
Preliminary Procedure
Trigger System Calibration
Horizontal System Calibration
SECTION 5 ELECTRICAL PARTS LIST
SECTION 6 DIAGRAMS AND CIRCUIT
BOARD ILLUSTRATIONS
SECTION 7 MECHANICAL PARTS LIST
CHANGE INFORMATION
NOTE
4-1
4-1
4-1
4-1
4-1
4-1
4-1
4-1
4-1
4-1
4-2
4-4
4-4
4-4
4-5
4-5
4-15
4-1 Refer to the 7B92 Operators manual for specifications
4-1 and complete operating information.

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DUAL TI ME B ASE
7892
78 92 Features
The 789 2 D ua l T im e B ase unit provides no r ma l, intensified, de layed, an d alternate sweep operation for T ektronix
7 ooQ · Se ri es O sc ill os copes. Ca librated sweep rat es from 0.2 second to 0.5 nanosecond and tri ggering to 500 mega h er tz are
pr ovi ded. The 7892 is intended for use with h ig h-f re quency lO OO -Series Osci ll oscope systems; however, most 789 2 functions
are compati bl e wi th a ll 7CXlO -Se ri es Osci ll oscopes.
Other featur es ind ude lighted push button switches, compatibility with osci ll oscopes having an alphanumeric r ea dout
system, and 0 to 9.9 times conti nuous sweep delay. A VAR IABLE control allows continuously variable sweep ra t es be tween
calibrated steps. Also, when operating in the A UT O MAIN TRI GG E RING MODE, a bright base line is displayed in the
absence
of a trigger si gnal.
7892
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Section 1-7892 Service
OPERATING INFORMATION
The 7B92 Dual Time Base unit operates with a Tektronix 7900-Series oscilloscope and a 7A-Series amplifier unit to form a
complete high-frequency oscilloscope system.
To effectively use the 7B92, its operation and capabilities should be known.
Brief operating information is given in this section. For more detailed instructions, refer to the 7B92 Operators Manual.
PRELIMINARY INFORMATION
Installation
The 7B92 is designed to operate in the horizontal
compartment
of the oscilloscope. This instrument can also
be installed in the vertical plug-in compartment to provide a
sweep that runs vertically on the CRT. However, when used
in this manner, there is no retrace blanking or internal
triggering,
and the unit may not meet the specifications
given in the Operators Manual. The. instructions in this
manual are written for use of the 7B92 in the horizontal
plug-in compartment.
Before proceed
ing with installation, check the settings of
the Variable Selector multi-pin connector and the Main-
frame Selector multi-pin connector (see Fig. 1-1). The
Variable Selector determines whether the front-panel
VARIABLE control operates in conjunction with the
Delaying
or Delayed Sweep. The Mainframe Selector
determines the oscilloscope in which the 7B92 is to be
operated; any 7900-Series Oscilloscope, or any other
7000-Series Oscilloscope.
CONTROLS AND CONNECTORS
General
All controls required for the operation of the 7B92,
except the Variable Time/Division Selector
and Mainframe
Selector, are located on the front panel of the instrument.
To make full use of the capabilities of this instrument, the
operator should be familiar
with the function and use of
each control. A brief description of the front-panel controls
and connectors is given here. More detailed information is
given in the 7B92 Operators Manual. Fig. 1-2 shows the
front-panel controls
and connectors of the 7B92.
G) Main Triggering Controls
LEVEL. Selects the amplitude point on the trigger signal
where sweep triggering occurs when operating in the
AUTO, NORM, or SINGLE SWEEP MAIN TRIGGERING
MODE. When operating in the HF SYNC MAIN TRIG-
GERING MODE, the LEVEL control adjusts the frequency
of the trigger generator to synchronize with the triggering
signal to provide a stable display.
SLOPE. Permits triggering on the positive or negative-
going portion of the trigger signal in all positions of the
MAIN TRIGGERING MODE switch except HF SYNC.
TRIG'D Light. Indicates that the sweep is triggered and
will produce a display with the correct setting of the
POSITION control and the controls of the associated
vertical units
and oscilloscope.
MODE.
Four pushbutton switches to select the desired
triggering mode. Selected mode
is indicated by lighted
pushbutton.
AUTO. Triggered sweep is initiated by the applied
trigger signal at a point selected by the LEVEL control
and SLOPE switch when the trigger signal repetition rate
is above 30 hertz and within the frequency range
selected
by the COUPLING switch. The sweep free-runs
to provide a reference trace under the following condi-
tions: When the LEVEL control is outside the amplitude
range, the trigger repetition rate
is outside the frequency
range selected by the COUPLING switch, or the trigger
signal is inadequate.
HF SYNC. Sweep initiated by trigger signals with
repetition rates above 100 megahertz and within the
range selected by the COUPLING switch. Stable displays
can be obtained when the LEVEL control adjusts the
frequency
of the trigger generator to the frequency (or
subharmonic)
of the trigger signal frequency. When the
LEVEL control is adjusted to frequencies between
subharmonics, the
sweep free- runs.
NORM. Sweep initiated by the applied trigger signal at a
point selected by the LEVEL control and SLOPE switch
over the frequency
range selected by the COUPLING
switch. Triggered
sweep can be obtained only over the
amplitude
range of the applied trigger signal. When the
LEVEL control is outside the amplitude range, the
trigger repetition rate
is outside the frequency range
selected by the COUPLING switch, or the trigger signal
is inadequate, there is no trace.
,-,
SCtmS bv Outsource-Qptlons =>

Operating Information-7B92 Service
MAINFRAME SELECTOR
P309
7900-S e ri es
MlIinframe
P309
P308
(Pin 1 to
front of instrument!
Delayed Sweep
Variable
(Pin 1 to
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ear of instrument)
Delaying Sweep
Variable
All othe,
7ooo.$",;e$
Oscilloscopes
VARIABLE SELECTOR
P308
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Fig. ' · 1. Locat ion of Variable Selector en d Mainframe Selector multi-pin connectors.
SI NG LE SWEEP-READY. After a sweep is dis·
played, further sweeps cannot
be presented unt il the
RESET button is pressed. Display is triggered as for
NORM operation, using the MAIN TRIGGER I NG con·
troi s. The S IN GLE SWEEP-READY li ght is illuminated
when the RESET pushbutton is pressed, and remains on
until a trigger is received and the sweep is completed.
'-2
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RESET. When the RESET pushbutton is pressed
(S I NG LE SWEEP MO DE), a single display is presented
(with proper triggering) when the
next trigger pulse is
received. The SINGLE SWEEP-READY light remains
on until a trigger is recei ved and the sweep is completed.
The RESET pushbutton must be pressed again before
another sweep can be presented.
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Operating Informati on-7 B9 2 Se rvice
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\::J CONNECTORS
DUAL TIME BASE
Fig. 1·2. Fron t·pane l co ntr ols and conn ec tors.
CO UPLING . Four pushbutton switches to select trigger
coupling. Selected coupling
is indicated by lighted push·
button.
AC. Rejects DC and attenuates AC signals below
about 30 hertz. Accepts signals between 30 hertz and
500 megahertz.
AC LF RE J. Rejects DC and attenuates signals below
about 30 kilohert z. Accepts signalsbetween 30 kilohertz
and 500 megahertz.
AC HF R
EJ. Rejects DC and attenuates signals above
50 kilohertz. Accepts signals from 30 hertz to 50
kilohertz.
DC . Accepts all signals from DC to 500 megahertz.
Sca n ... by OUlsourcl!-Oplions ->
SOURCE. Four pushbutton switches that select the trig·
gering source. Selected source is indicated by lighted
pushbutton.
IN T. Trigger signal obtained internally from vertical
unit by way of associated oscilloscope.
LI
NE. Tr igger signal obtained internal ly from a
sample of the line voltage applied to the associated
oscilloscope.
EXT. Trigger signal obtained from an external signal
applied to the
MA IN TRIG IN connector.
EXT + 10. Trigger signal obtained from an external
signa l applied to the MAIN IN connector. In this
position the external signal
is attenuated 10 times before
it
is applied to the trigger circuit.
' -3

Op erating Inf ormation-7B92 Service
® Sweep Controls
TIME!DIV OR DLV TIME. Se lects the basic sweep r at e
f or Norm al and ALT Sweep operation and se lects the delay
time
(to be multiplied by the DEL AV T IM E MULT dial
setting) wh
en operating in the INTEN or DL V'D Sweep
mode (see F ig. ' ·3) . The VAR IA BL E control must be in
the CAL position for the in dicated sweep rate.
DLV'D Tim
e/ Di vision. Selects the 9Neep rate of the
de layed 9Neep ge nerator for operation in the DLV'D
Sweep, INTEN, and ALT Sweep Di splay Modes (s ee
Fig. ' ·3). The VAR I AB LE cont rol must be in the CAL
positi on f or ind i cat i ng the sweep rate.
VARIABLE. Two·position 9Nitch actuated by the
VAR I AB LE control to sel ect calibrat ed or uncatibrated
sweep rates (see Fig. '·3). In the CAL position (pressed in)
the VAR I
AB LE control is inoperati ve and the sw e ep rate is
calibrated. When pressed and released, the knob moves
ou t
to activate the VAR IABLE contro l for uncalibrated sweep
rates. The sweep rate in each Tl
ME /DIV switch positi on
can be reduced at least to the 9Nee p r ate of the next slower
position. T
he VA RI AB LE control can be sw itched to
operate with either the de laying or de layed 9Neeps by
means
of the internal Variable Select or multi·pin con·
nectar.
Di splay Mode s. F our display modes can be selected by
the follOWing switch settings:
SWP VAR I ABLE {C AL IN t
CAl TIME/DIY OR DLY
ALT ( OUT I o
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NORMAL Sweep. A Normal Sweep (non·delayed) is
selected when the TI ME /DIV OR Dl V TI ME switch and
the Dl V'D Time/ Divisi
on switch are locked together at
the same sweep rate (see F
ig. ' ·3). T he Dl V'D Time!
Division switch and the Delayed Triggering l E
VE L
contro l must be pressed in for the Normal Swe ep Mode.
Calibrated sweep rates from 0.2 second/ di visi on to 0.5
nanosecond/division can be obtained.
IN TEN. T he tNTEN mode, a function of the
de laying and delayed 9Neeps is selected whe n the DLV'D
Ti me/Divisi on mitc h is pulled out and rotated clockwise
(see Fig. ' ·
3). In th is mocle, a portion of the delaying
sweep is intensified during
the time that the delayed
sweep generator runs.
DL V'O Sweep. Th e Dl V'D Sweep Display Mode is
selected when the DL V'D Time/Division switch is pulled
out , rotated in the INT EN Display Mode for the desired
de layed sweep rate, then pushed in (see Fig. ' ·3). ln this
Displ ay Mode, the delayed 9Neep is displayed, at a r ate
determined by the DL V' D Time/ Division 9Nitch, at the
end of each delay period, as selected by the T IME / DIV
OR Dl V TI ME switch and the DE LAV T IME MUL T
dial settings.
AL T Sweep. When the ALT switch is pressed and
re leased to the OU T position, sweeps from bot h the
delaying sweep generator
(i ntensified sweep) and de ·
layed SNeep gener ator (delayed $\Neep) are displayed.
Sw i lch
$W eep r ite
u pon i I
NORMAL Sweep, INTEN ,
Displ ay M odes .
Fig. 1·3.
Composi te Ti me /D iv ision swi tch.
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The alternate sweep switches between generators at the
end of each sweep. The TRACE SEP control is activated
in this Display Mode.
TRACE
SEP. When the AL T switch is OUT (AL T
Sweep Display Mode), it serves as a trace separation
control. This control vertically positions the trace (pro-
duced
by the delaying sweep generator) up to four divisions
with respect to the trace produced by the delayed sweep
generator.
DELAY TIME MUL T. Provides variable delay of 0 to
9.9 times the basic delay time selected by the TIME/DIV
OR DLY TIME switch.
INTENSITY. Controls the intensity of the delaying
sweep display only, when operating in the INTEN or AL T
Sweep Display Modes.
SWP CAL. Screwdriver adjustment to set horizontal gain
of unit. The SWP CAL is used to set the basic timing of the
7B92
and to compensate for differences in input sensitivity
when changing oscilloscopes.
o Delayed Triggering Controls
LEVEL. Control determines delayed sweep mode, de-
layed trigger mode
and delayed trigger level.
®
IN-RUNS AFTER DL Y TIME. The delayed sweep
runs immediately
following the delay time selected by
TIME/DIV OR DLY TIME switch and the DELAY
TIME MULT dial. Delayed SLOPE,COUPLlNG, SOURCE,
and HF SYNC functions are inoperative.
OUT-DLY'D SWP TRIGGERABLE. When the De-
layed Triggering
LEVEL control is pressed and released,
the delayed
sweep is triggerable. The Delayed Triggering
LEVEL control can now be rotated to select the
amplitude
point on the trigger signal at which the
delayed
sweep is triggered, or it can be rotated counter-
clockwise
(as marked on the instrument front panel) to
select the HF SYNC Delayed Triggering Mode. In the
OUT-DLY'D SWP TRIGGERABLE mode, the delayed
SLOPE, COUPLING, and SOURCE functions are ac-
tivated.
HF SYNC. The
HF SYNC Delayed Triggering Mode
is selected when the Delayed Triggering LEVEL control
is pressed and released to the OUT-DL Y'D SWP TRIG-
GERABLE position and rotated counterclockwise to HF
SYNC, as marked on the instrument front panel. Sweep
is initiated by trigger signals with repetition rates above
Scans by Ou!so",ce-Qptlo1l$ =>
Operating Information-7B92 Service
100 megahertz and within the range selected by the
COUPLING switch. Stable display can be obtained when
the
LEVEL control adjusts the frequency of the trigger
generator
to the frequency (or subharmonic of the
trigger signal frequency. When the
LEVEL control is
adjusted to frequencies between subharmonics, the
sweep free-runs.
SLOPE. Two-position switch to select the portion of the
trigger signal
wh ich starts the delayed sweep.
+. The delayed sweep can be triggered from the
positive slope
of the trigger signal.
-. The delayed sweep can be triggered from the
negative slope
of the trigger signal.
COUPLING. Two-position switch
that determines the
method
of coupling the delayed trigger signal to the
delayed trigger circuit.
AC. Rejects DC and attenuates signals below about
30 hertz. Accepts delayed trigger signals from 30 hertz
to 500 megahertz.
DC. Accepts trigger signals from DC to 500 Megahertz.
SOURCE. Two-position switch that selects the source of
the delayed trigger signal.
INT. The delayed trigger signal is obtained from the
vertical amplifier
unit by way of the associated oscillo-
scope.
EXT. The delayed trigger signal is obtained from an
external signal applied to the DLY'D TRIG IN con-
nector.
o Front-Panel Inputs
MAIN TRIG IN. When the SOURCE switch for MAIN
TRIGGERING is set to EXT or EXT -;. 10, this connector
serves as an external trigger input for the main triggering
circuit.
DLY'D TRIG IN. When the Delayed Triggering
SOU RCE switch is set to EXT, this connector serves as an
external trigger input for the delayed triggering circuit.
TERM
50 il 1 Mil. Two position switch to select
50 ohm or one megohm input impedance for the MAl N
TRIG IN and DL Y'D TRIG IN connectors.
1-5

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Section 2-78,92 Service
CIRCUIT DESCRIPTION
The follQ,win
g discussion
is provided t~ a.id in underst.anding the overall.co~c~Pt of the 7B92. A basic block diagram of the
7892 is shown in Fig. 2·1. Only the basIc mterconnectlons between the mdlvldual blocks are shown. The number on each
block (enclosed in diamond) refers to the complete circuit diagram located at the rear of this manual.
Block Diagram Description
The Main Trigger Generator includes circuitry for
selecting trigger source, type of coupling, triggering mode,
and point
on the trigger signal where triggering occurs.
Also, regardless of the trigger signal, shape, or amplitude
(within specification) the Main Trigger Generator provides a
fast-rise uniform amplitude pulse
to the Delaying Sweep
Start Comparator. Termination of the gate pulse occurs at
the rise of Delaying Sweep Holdoff.
The Delaying Sweep Start Comparator is activated by
the positive gate from
the Main Trigger Generator. The
output gate, coupled to the Delaying Sweep Generator, is
the same duration as the delaying sweep. This gate is also
coupled
to the Aux Sweep Gate connector and to Display
Mode Switching for Alternate Sweep operation.
The delaying sweep sawtooth signal
is generated when
the gate from the Delaying Sweep
Start Comparator is
applied to the Delaying Sweep Generator. The sawtooth
duration
is determined by the gate duration; the rate of
change
of the sawtooth is set by Ct and Rt, selected by the
TIME/DIV OR DL Y TIME switch. The delaying sweep
sawtooth signal
is coupled to the Horizontal Output
Amplifier, the Delaying Sweep Stop Comparator, the Delay
Pickoff circuits, and the Delaying Sweep Out connector.
One side of the Delaying Sweep Stop Comparator is
driven by the delaying sweep sawtooth signal and the other
side is set by the Delaying Sweep Length adjustment. When
the sawtooth waveform passes through
the setting of the
Delaying Sweep Length adjustment the output of the
comparator switches to a positive level.
The positive level from the sweep stop comparator
initiates the positive holdoff gate. The duration
of the
holdoff gate is variable, depending on the setting of the
TIME/DIV switch. Holdoff timing capacitors are separate
from sweep timing capacitors. Holdoff
is longer for slower
sweep rates. Output from the delaying sweep holdoff is
coupled to the Main Trigger Generator, the Delayed Trigger
Generator, and the Holdoff
out connector. A sweep gate
cannot be generated during
the holdoff interval. When the
holdoff falls, the trigger circuits are reset so that they are
ready
to receive a trigger signal.
®
The Lockout Amp processes mainframe logic signals
(when operating the mainframe in the alternate or delaying
Horizontal Modes)
to provide a sweep disable pulse to the
Main Trigger Generator.
The Horizontal
Output amplifier provides positioning
and amplification
of the sawtooth signals. Display Mode
Switching works
in conjunction with the Horizontal Output
to provide NORMAL Sweep, INTEN, DLY'D Sweep and
AL T Sweep Display Modes.
The Delay Pickoff circuits produce a delay gate when
the delaying sawtooth signal passes through
the LEVEL
selected by the DELAY TIME MUL T dial. The gate ends
with
the delaying sawtooth signal. The output gate is
coupled to the Delayed Trigger Generator.
The Delayed Trigger Generator includes circuitry for
selecting delayed sweep mode, delayed trigger mode,
delayed trigger source, type of coupling, and the point on
the trigger signal where sweep triggering occurs. When the
Delayed Trigger LEVEL is at the RUNS AFTER DL Y
TI ME detent, the output sweep gate is generated as soon as
the delay gate signal (from the Delay Pickoff circuits) is
applied. When the Delayed Trigger LEVEL is in the DL Y'D
SWP TRIGGERABLE position, the output trigger is
initiated by the next input trigger signal after the delay gate
is applied. The delayed sweep trigger is terminated by the
holdoff signal. The trigger signal is coupled to the Delayed
Sweep
Start Comparator.
The Delayed Sweep
Start Comparator is activated by the
signal from the Delayed Trigger Generator. The output gate
coupled to the Delayed Sweep Generator, is the same
duration
as the delayed sweep. The delayed sweep gate
signal is also coupled to the Sweep Gate Generator.
The delayed sweep sawtooth signal is developed by the
Delayed Sweep Generator. The sawtooth is generated
during the time
that a gate is applied from the Delayed
Sweep
Start Comparator. Rate of change of the sawtooth is
set by Ct and Rt, selected by the DL Y'D TIME/DIV switch.
The delayed sawtooth
output is coupled to the Horizontal
Output Amplifier and the Delayed Sweep Stop
Comparator.
2-1
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EXTERNAL
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TRIGGER
MAIN
TRIG
IN
+. INTERNAL
~ TRIGGER
A20
B20
DLY'D
TRIG
IN
" INTERNAL
." TRIGGER
"
•
EXTERNAL L...e
" TRIGGER
SWEEP
LOCKOUTtlLE
f
AMP
~
DELAYING
SWEEP
HOLDOFF
r+-
~
MAIN DELAYING
TRIGGER SWEEP START
GENERATOR
f+- COMPARATOR
~
0
TRIGGER
DISABLE
C
DELAYED DELAYED
TRIGGER SWEEP START
GENERATOR COMPARATOR
~ 0
,
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DELAY
IDELAY I PICKOFF
14-
TIME
~
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HOLD OFF
, B
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+5V
DELAYING
_~ DELAYING
SWEEP STOP
COMPARATOR SWEEP
0
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j AUXILIARY SWEEP GATE
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/
DELAYING
SWEEP DELAYING SWEEP "
GENERATOR
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MODE
SWITCHING
0
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HORIZONTAL +SIGNAL OUT ,
OUTPUT /
AMPLIFIER
IDEALIZED TIMING WAVEFORMS
(")
:::;;'
DISPLAY MODE 2
INTEN DL Y'D SWP NORMAL SWp ;:i:
(delaying (delayed (delayed C
sweep -eep -eep ~
genarator) genarator) generator) ...
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DELAY TIME MUL T setting-2.00
DLY to DLY'D TIME/DIV ratio-2:1

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One side of the Delayed Sweep Stop Comparator is
driven by the delaying sweep sawtooth signal; the other side
is set by the Delayed Sweep Length Adjustment. When the
delayed sawtooth waveform passes through the voltage set
by the Delayed Sweep Length Adjustment,
the comparator
switches
to a positive level. This positive level is coupled to
the Sweep Gate Generator.
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Circuit Description-7B92 Service
The Sweep Gate Generator produces an unblanking
pulse for the associated oscilloscope. The Sweep Gate pulse
is initiated by the gate from the Delayed Sweep Start
Comparator and terminated
by the pulse from the Delaying
Sweep Stop Comparator or Delayed Sweep Stop Compara-
tor (wh ichever occurs first).
2-3

Section 3-7892 Service
MAINTENANCE
This section of the manual contains maintenance information for use in preventive maintenance, corrective maintenance,
and troubleshooting
of the 7892.
PREVENTIVE MAINTENANCE
General
Preventive maintenance consists of cleaning, visual
inspection,
lubrication, etc. Preventive maintenance per·
formed on a regular basis may prevent instrument break·
down and will improve the reliability of this instrument.
The severity of the environment to which the 7892 is
subjected determines the frequency of maintenance. A
convenient
time to perform preventive maintenance is
preceding recalibration of the instrument.
Cleaning
The 7892 should be cleaned as often as operating
conditions require. Accumulation of dirt in the instrument
can cause overheating and component breakdown. Dirt on
components acts as an insulating blanket and prevents
efficient heat dissipation. It may also provide an electrical
conduction path.
The covers
of the oscilloscope reduce the amount of
dust that reaches the interior of the 7892. Operation of the
system without the oscilloscope covers in place necessitates
more
frequent cleaning. When the 7892 is not in use, it
should be stored in a protected location, such as a
dust-tight cabinet.
Avoid the use of chemical agents which might damage
the plastics used in this instrument. Avoid chemicals
which contain benzene, toluene, xylene, acetone, or
similar solvents.
Exterior. Loose dust accumulated on the outside of the
7892 can be removed with a soft cloth or small paint brush.
The
paint brush is particularly useful for dislodging dirt on
and around the front-panel controls. Dirt that remains can
be removed with a soft cloth dampened in a mild detergent
and water solution. Abrasive cleaners should not be used.
Interior. Dust in the interior of the instrument should
be removed occasionally, due to its electrical conductivity
under high-humidity conditions. The best way to clean the
interior is to blow off the accumulated dust with dry
®
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low-velocity air. Remove any dirt that remains with a soft
paint brush or a cloth dampened with a mild detergent and
water
solution. A cotton-tipped applicator IS useful for
cleaning in narrow spaces.
Visual Inspection
The 7892 should be inspected occasionally for such
defects
as broken connections, broken or damaged circuit
boards, improperly seated transistors or relays, and heat-
damaged parts.
The corrective procedure
for most visible defects is
obvious; however, particular care must be taken if heat-
damaged components are found. Overheating usually
indicates
other trouble in the instrument; therefore, it is
important that the cause of overheating be corrected to
prevent recurrence of the damage.
Semiconductor Checks
Periodic checks of the transistors, FEr's, and IC's used
in the 7892 are not recommended. The best indication of
performance is the actual operation of the device in the
circuit. Performance of the circuits is thoroughly checked
during recalibration; substandard semiconductors will
usually be detected at that time.
Recal ibration
To ensure accurate measurements, check the calibration
of this instrument each 1000 hours of operation or every
six
months if used infrequently. In addition, replacement of
components may necessitate recalibration of the affected
circuits.
Calibration instructions are given in Section 4.
TROUBL ESHOOTI NG
Introduction
The following information is provided to facilitate
troubleshooting of the 7892. I nformation contained in
other sections of this manual should be used along with the
following information to aid in locating the defective
component.
An understanding of the circuit operation is
very helpful in locating troubles. See the Circuit Descrip-
tion section.
3-1

Maintenan ce- 7B92 Se rvi ce
Troubl es hooting Aids
Diagrams. Circuit diagrams are given on foldo ut pages in
Section 6. T
he component number and electrical va l ue of
eac h component in this instrument is shQlNn on the
diagrams.
Ci rcuit Board s. Fig. 6-2 (located in the diagrams
sect ion) shows the location of the circuit boards wit hin this
instrument along
with the assembly numbers. The assemb ly
numbers are used on the diagrams to aid in locating the
boards. Pictures of the circuit boards are shQlNn in the
Diagrams section, on the back
of the page opposite the
circuit diagram, to aid in crosHefe rencing between the
diagrams and the cir
cuit -board pictures. Each electri cal
component o.)n the boards is identified by its circuit
number,
as well as the interconnecting wire or connectors.
The diagrams are
outlined with a blue line to show which
portions of the circuit are located on a circuit board.
Switch Cam Ide ntification . Switch cam numbers shown
on the diagrams indicate the position
of the cam in the
complete switch assembly. The switch cams are number ed
from fron t to rear.
Diode Color Cod
e. T he cathode end of each glass
encased diode is identified by a stripe, a series of stripes, or
a dot. Fo r most si licon or germanium diodes wit h a series of
stripes, the color code also indicates the type of diode or
identifies the T
ekt r onix Pa rt Number using the resistor
color-code sys t em (e.g., a diode color coded blue-or
pink-brown·gray.green indicates Tektron ix Part Number
152·01
85·00). The cathode and anode ends of a metal
encased diode can be identified by the diode symbol
mark
ed on the body.
Wiring Color Code and Multi -Connector Id e nti -
fi ca tion . Insulated wire and cable used in the 7892 is col or
coded to aid circuit tracing. Multi ·connector holders are
keyed with twO triangl es (or a triangle and a do t), one on
the connector
ho lder and one on the circuit board. The
tr iangle on the multi - co nnector holder must match wi th the
triangle on the ci
rcuit board for normal circuit operation.
In special cases where multi -connect or holders are used as a
switch, the triangles may
not match (see Operating Instruc·
tions for special multi·connector ho lder functions). The
color of the multi ·connector ho lder corresponds to the last
numeral
of the circuil number, using the EIA color code
(e.g., P22 is red).
Interface Co nn ec tor Pin loca ti on s. The Interface circuit
board couples the 7892 to the associated oscilloscope. Fig.
3·1 illustrates the locations of pins on the interface
connector
as shown on the Voltage Distribution and
Output Connectors schematic in the diagrams section.
3-2
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Troubleshooting Equipment
Th e f ollowing equipment is useful for troubleshooting
the
7892.
1. Transistor Tester
D
esc r ip tion: Tektronix Type 577 Transistor·Curve
Tracer or a 7C Tl N Curve Tracer plug·in unit and a
7000 -$eries Oscilloscope system.
Purpose: To test semiconductors used in this instru·
ment.
2. Volt·ohmmeter
Descriptio n: 20,000 ohms/volt. 0·500 volts DC.
Accurate
within 3%
Purpose: To measure voltages and resistance.
3. Test Oscilloscope
Description: DC
to 100 megahertz frequency response,
five millivo l ts to fi ve vo lt s/division. U se a 10X probe.
Purpose: To check the waveforms in the instrument.
4. Plug·ln Extender
Description: Rigid plug·in extender, Tektronix Part
Number 067·0589·00.
Purpose: Permits operation of the 7892 outside the
plug· in compartment of t he oscilloscope for better
access during troubleshooting.
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Fig. 3· 1. l oca 1 io n 01 pins on In1e rl aee eo nn ec tor.
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Troubleshooting Techniques
This troubleshooting procedure is arranged in an order
which checks the simple
trouble possibilities before pro-
ceeding with extensive troubleshooting. The first few
checks ensure proper connection, operation,
and calibra-
tion. If the trouble is not located by these checks, the
remaining steps aid in locating the defective component.
When the defective component
is located, it should be
replaced following the replacement procedures given under
Corrective Maintenance.
1. Check Control Settings. Incorrect control settings
can indicate a trouble that does not exist. If there is any
question about the correct
function or operation of any
control, see the Operating Instructions.
2. Check Associated Equipment. 8efore proceeding
with troubleshooting of the 7892, check that the equip-
ment used with this instrument is operating correctly.
Check that the signal is properly connected and the probe
(if used) is not defective. The oscilloscope and vertical
plug-in
unit can be checked for proper operation by
substituting another time-base unit that is known to be
operating properly (preferably another 7892 or similar
unit). If the trouble persists after substitution, the oscillo-
scope or vertical plug-in unit should be checked.
3. Check Instrument Calibration. Check the calibration
of this instrument, or the affected circuit if the trouble
exists in one circuit. The apparent trouble may only be a
result of misadjustment that can be corrected by calibra-
tion. Complete calibration instructions are given in the
Calibration section.
4. Visual Check. Visually check the
portion of the
instrument in which the
trouble is located. Many troubles
can be located by visual indications such as unsoldered
connections, broken wires, damaged components, etc.
5. Isolate Trouble
to a Circuit. To isolate a trouble to a
particular circuit, note the trouble symptom. The symptom
often indicates the
circuit in which the trouble is located.
For example, if stable triggering can be obtained in the I NT
position of the SOURCE switch and cannot be obtained in
the
EXT or LINE positions, the External Trigger Preamp or
Trigger Source Switching circuits are probably at fault.
When the trouble symptoms appear, use the front-panel
controls
and the CRT display to isolate the trouble to one
circuit. Keep the amplifier
unit and oscilloscope in mind
when isolating the trouble. When
trouble appears in more
than one circuit, check all affected circuits
by taking
voltage and waveform measurements. Once the defective
circuit has been located, proceed with steps 6 and 7 to
locate the defective component(s).
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Maintenance-7B92 Service
6. Check Individual Components. The following pro-
cedures describe methods of checking individual com-
ponents in the 7892. Components that are soldered in place
are best checked by disconnecting one end. This isolates the
measurement
from the effects of surrounding circuitry.
a. Relay. The eight pin relay used in the 7892 is
symmetrical and may be replaced in its socket facing
either direction. This relay, which
is plugged into the
circuit board, may be removed and checked. Use an
ohmmeter to check the 600 ohm resistance. The relay
may also be actuated by placing the +15 volts across the
coil. The internal connections are printed on the body of
the relay.
b. Transistors. The best check of transistor opera-
tion is actual performance under operating conditions. If
a transistor is suspected of being defective, it can best be
checked by substituting a new component or one that
has been checked previously. However, be sure that
circuit conditions are not such that a replacement
transistor might also be damaged. If substitute transis-
tors
are not available, use a dynamic tester (such as a
Tektronix Type 577 or 7CT1N Curve Tracer plug-in unit
and a 7000-Series Oscilloscope system.
c. Integrated Circuits. Integrated circuits should not
be replaced unless they are actually defective. The best
method
for checking these devices is by direct substitu-
tion with a new component or one that is known to be
good. 8e sure that circuit conditions are not such that a
replacement component might be damaged.
d. Diodes. A diode
can be checked for an open or
shorted condition by measuring the resistance between
terminals. Using an ohmmeter scale having an internal
source of between 800 millivolts and 3 volts, the
resistance should
be very high in one direction and very
low when the leads are reversed.
~
Do not use an ohmmeter scale thathas a high internal
current.
High currents may damage the diode.
e. Resistors. Resistors can be checked with an ohm-
meter. Check the Electrical Parts List for the tolerance
of the resistors used in this instrument. Resistors
normally do not need to be replaced unless the measured
value varies widely from the specified value.
f. Inductors. Check for open inductors by checking
continuity with an ohmmeter. Shorted or partially
shorted inductors can usually be found by checking the
waveform response when high-frequency signals
are
passed through the circuit. Partial shorting often reduces
high-frequency response.
3-3

Maintenance-7B92 Service
g. Capacitors. A leaky or shorted capacitor can best
be detected by checking the resistance with an ohm-
meter on the highest scale. Do not exceed the voltage
rating of the capacitor. The resistance should be high
after the initial charge of the capacitor. An open
capacitor can
best be detected with a capacitance meter
or by checking whether the capacitor passes AC signals.
7. Repair and Readjust the Circuit. If any defective
parts are located, follow the replacement procedures given
in this section. Be sure to check the performance of any
circuit that has been repaired, or that has had any electrical
components replaced.
CORRECTIVE MAINTENANCE
General
Corrective maintenance consists of component replace-
ment and instrument repair. Special techniques required to
replace components in the instrument are given here.
Obtaining Replacement Parts
All electrical and mechanical part replacements for the
7B92 can be obtained through your local Tektronix Field
Office
or representative. However, many of the standard
electronic components can be obtained locally in less time
than is required to order them from Tektronix, Inc. Before
purchasing
or ordering replacement parts, check the parts
list for value, tolerance, rating, and description.
NOTE
When selecting replacement parts, it is important to
remember
that the physical size and shape of a
component may affect the performance in the instru-
ment, particularly at high frequencies. All replace-
ment parts should be direct replacements unless it is
known that a different component will not adversely
affect instrument performance.
When ordering replacement parts from Tektronix, Inc.,
include the following information.
1. I nstrument Type.
2. Instrument Serial Number.
3. A description
of the part (if electrical, include circuit
number).
4.
Tektronix Part Number.
3-4
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Component Replacement
I WARNING]
Disconnect the equipment from the power source
before replacing components.
Relay Replacement. The relay in the 7892 is manu-
factured by Tektronix, Inc. If the relay fails, a replacement
may be ordered from your local Tektronix Field Office or
representative. The eight-pin DPDT relay may be replaced
in its socket either way, since this relay is symmetrical.
Semiconductor Replacement. Semiconductor devices
used
in this instrument should not be replaced unless
actually defective. If removed from their sockets during
routine maintenance, return them to their original sockets.
Unnecessary replacement may affect
the calibration of this
instrument. When a semiconductor is replaced, check the
operation of the part of the instrument that may be
affected.
Replacement devices should be of the original type or
direct replacement. Re-install in the same manner as the
original. Fig. 6-1 (located in diagrams section) shows the
lead configurations of the semiconductor devices used in
this instrument. When replacing, check the manufacturer's
basing diagram for correct basing.
Interconnecting Pin Replacement. Two methods of
interconnection are used
in this instrument to connect the
circuit boards with other boards and components. When the
interconnection is made with a coaxial cable, a special
end-lead connector plugs into a socket on the board. Other
interconnections are made with a pin soldered onto the
board. Two types of mating connectors are used for these
interconnecting pins.
If the mating connector is mounted
on a plug-on circuit board, a special socket is soldered into
the board. If the mating connector is on the end of a lead,
an end-lead pin connector is used that mates with the
interconnecting pin. The following information provides
the replacement procedure for the various interconnecting
methods.
a. Coaxial-Type End-Lead Connectors.
Replacement of the coaxial-type end-lead connectors
requires special tools and techniques; only experienced
maintenance personnel should
attempt replacement of
these connectors. It
is recommended that the cable or
wiring harness be replaced as a unit. For cable
or wiring
harness
part numbers, see the Mechanical Parts List. An
alternate solution is to refer the replacement of the
defective connector to your Tektronix Field Office or
representative.
®

®
b. Circuit Board Pins and Pin Sockets.
~....r''''''''''
) CAUTION ~
~~,
The fol/owing procedures are recommended for
single-layer circuit boards only. Pin and socket
replacement on multi-layer
circuit boards should be
performed
only by specialized service personnel.
Refer to
your local Tektronix Field Office or Service
Center.
A circuit board pin replacement kit including neces-
sary tools, instructions, and replacement pins is available
from Tektronix, I nco (Tektronix Part No. 040-0542-00).
To replace a pin which is mounted on a circuit board,
first disconnect any pin connectors. Then, unsolder the
damaged pin and pull it out of the circuit board with a
pair
of pliers. Be careful not to damage the wiring on the
board
with too much heat.
Ream
out the hole in the circuit board with a
0.031-inch drill. Remove the ferrule from the new
interconnecting
pin and press the new pin into the hole
in the circuit board. Position the pin in the same manner
as the old pin. Then, solder the pin on both sides of the
circuit board. If the old pin was bent at an angle to mate
with a connector, bend the new pin to match the
associated pins.
The
pin sockets on the circuit boards are soldered to
the rear of the board. To replace one of these sockets,
first unsolder the pin socket (use a vacuum-type desol-
dering tool to remove the excess solder). Then straighten
the tabs on the socket and remove
it from the hole in
the board. Place the socket in the
circuit board hole and
press the tabs
down against the board. Solder the tabs of
the socket to the circuit board; be careful not to get
solder into the socket.
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Maintenance-7B92 Service
NOTE
The spring tension of the pin sockets ensures a good
connection between the
circuit board and the pin.
This spring tension can be destroyed by using the pin
sockets as a connecting point for spring-loadedprobe
tips, alligatorclips, etc.
c. End-Lead Pin Connectors.
The
pin connectors used to connect the wires to the
interconnecting pins are clamped
to the ends of the
associated leads.
To replace damaged end-lead pin
connectors, remove the old pin connector from the end
of the lead and clamp the replacement connector to the
lead.
Some
of the pin connectors are grouped together and
mounted in a plastic
holder; the overall result is that
these connectors are removed and installed as a multi-pin
connector. To provide correct orientation of this multi-
pin connector when it is replaced, an arrow (or dot)
is stamped on the circuit board and a matching arrow is
molded into the plastic housing of the multi-pin
connector. Be sure that these arrows are aligned when
the multi-pin connector is replaced. If the individual
end-lead
pin connectors are removed from the plastic
holder, note the color of the individual wires for
replacement.
Switch Replacement. Pushbutton switches and a cam-
type switch are used in the 7B92. It is recommended that
both switch types be replaced as a unit. Refer to Fig. 3-2
for cam-switch removal and to Fig. 3-3 for pushbutton
switch removal.
3-5

Maintenance-7B92 S .
ervlce
Scansb 0v "tsource-Options =>
LOOSE
PART
Fig. 3·2
. Cam·switch
removal.
®

Maintenance-7B92 Service
®
CAUTION
Repair of the cam switch should only be undertaken by skilled maintenance personnel. Switch alignment and contact
spacing must be carefully maintained for proper operation of the switch. The cam switch repair kit (Tektronix Part
Number 040·0541·001 contains special alignment tools for use in repairing or replacing the cam and contacts. For
information or assistance on maintenance of the cam switch, contact your local Tektronix Field Office or representative.
The cam switch (TIME/DIV OR DLY TIME and DLY'D Time/Divisionl consists of two rotating cams (front portion for TlME/DIV
OR DLY TIME and rear portion for DL Y'D Time/Divisionl, which are turned by front·panel knobs and contacts mounted on the
adjacent Interface board. These contacts are actuated by lobes on the cam as it is turned. The switch can be disassembled for inspection,
cleaning, repair, or replacement; but it is recommended that the switch be removed from the instrument only as a unit.
NOTE
Before removing switch and control knobs, note the position of the knob to facilitate replacement and to assure proper
alignment.
1. Set the TIME/DIV OR DLY TIME and DLY'D Time/Division switches to .2 s to provide easy access to the screw on the
clear plastic flange (rear of subpanell and to facilitate replacement of the switch.
2. Press in the DLY'D Time/Division switch. Loosen the set screws and remove the VARIABLE and DLY'D Time/Division
knobs.
3. Remove the set screw from the rear of the front·subpanel and remove the clear plastic flange associated with the TIME/DiV OR
DLY TIME assembly.
4. Disconnect the necessary cables from the Main Trigger circuit board to allow removal of the cam switch assembly.
5. Rotate the VARIABLE Time/Division switch to expose the set screw holding the shaft of R200. Loosen the set screw to allow
cam switch removal.
6. Disconnect the two cables from the Sweep board and completely loosen the six screws holding the Sweep board. Carefully lift the
sweep board from the instrument; do not bend pins from the I nterface board to the Sweep board.
7. Remove the 10 set screws holding the cam switch to the Interface board. Hold the cam switch while removing the screws.
CAUTION
Do not remove ten screws holding Readout board to cam·switch.
8. Remove the cam switch assembly from the Interface board.
9. Follow the procedure as given in the switch repair kit to remove, replace, etc., the contacts on the Interface board.
10. To replace the cam switch, reverse the above procedure. Make sure that the clear plastic flange and the DL Y'D Time/Division
knob are replaced at the same switch position from which they were removed (.2 slDIV with DL Y'D Time/Division switch pushed inl.
CAUTION
When replacing the 10 screws to the Interface board, tighten evenly. When replacing the Sweep board, do not apply much
pressure until it is certain all pins from the Interface board have mated with the connectors on the Sweep board.
Fig. 3·2 (cont.)
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3·7