Tektronix 7B92 User manual

TE}<TFItrINI)@
INSTRUCTION IVANUAL
Tektronix, lnc.
P.O. Box 500
Beaverton, Oregon 97005
070-1192-00
Serial Number Do5]l{)D
373
7
DUAL T1ME BASE
SERVICE
2
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I
I. ,,'.lo*'o*'Y
All TEKTRONIX . instruments are warranted agairst
detective materials ind workmanstrip lor one yeat. Any
questions with respect to the warranty should be taken up
with your TEKTRONIX Field Engineer or represenlative.
All requests for repair and replacement parts $lould bq
directed to the TEKTBONIX Field Office or representative
in your area. This will assure you the fastest possible
service. Plea:tl ilslude the instrument Type NumbQt.oi.,Palt
Number and Seritl. Nlmber with all reque3ts forli?arts br
servics. . ', '
Specifications and price change privileges reserved.
copyright @ tgz: uv Tektronix, lnc., Beaverton, Or€gon.
Printed in the United States oI America. All rights reserved.
Contents of this publication may not be reproduced in any
lorm without permission of Tektronix. lnc.
U.S.A. and Foreign TEKTRONIX products covered by U.S
and foreign patents and/or patents pending.
TEKTRONIX is a registered trademark o, Tektronix, lnc.
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7892 Service
TABLE OF CONTENTS
OPERATING INFORMATION
Preliminary lnformation
lnstallation
Controls and Connectors
General
Main Triggering Controls
Sweep Controls
Delayed Triggering Controls
Front-Panel lnputs
Preventive Maintenance
General
Cleaning
Visual lnspection
Semiconductor Checks
Becalibration
Troubleshooting
lntroduction
Troubleshooting Aids
Troubleshooting Equipment
Troubleshootinq Techniques
Corrective Maintenance
General
Obtaining Beplacement Parts
Component Replacement
SECTION 4 CALIBRATION
Page
1-t
1-1
1.1
1-1
1-1
1-4
1.5
1-5
4-1
4-1
+1
4-1
4-1
+1
+1
+1
4-1
Using This Procedure
General
lndex
Performance Check
Partial Calibration
Complete Calibration Procedu re
Test Equipment Required
General
Special Calibration Fixtures
Calibration Equipment
Alternatives
Test Equipment
Calibration Procedure
lntroduction
lndex to Calibration Procedure
Preliminary Procedure
Trigger System Calibration
Horizontal System Calibration
SECTION 2 CIRCUIT DESCRIPTION
Block Diagram Description
SECTION 3 MAINTENANCE
2-1
3-1
3-1
3.1
3.1
3-1
3-1
3.r
3-1
3-2
3-2
3-3
3-4
3-4
3-4
3-4
Calibration lnterval
Tektronix Field Service 4-1
+1
4.1
4-2
4.4
+4
4.4
4-5
4.5
4.15
SECTION 5 ELECTRICAL PARTS LIST
SECTION 6 DIAGRAMS AND CIRCUIT
BOARD ILLUSTRATIONS
SECTION 7 MECHANICAL PABTS LIST
CHANGE INFORMATION
NOTE
Refer to the 7892 Operators manual for specifications
and complete operating inf ormation.
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OUAL TIME BASE
7Bg2
7892 Features
The 7892 Dual Time Base unit provides normal, intensified, delayed, and alternate sweep operation for Tektronix
7000-Series Oscilloscopes. Calibrated sweep rates from 0.2 second to 0.5 nanosecond and triggering to 500 megahertz are
provided. The 7892 is intended for use with high-frequency 7000-Series Oscilloscope systems; h owever, most 7892 functions
are compatible with all 7000-Series Oscilloscopes.
Other features include lighted pushbutton switches, compatibilitV with oscilloscopes having an alphanumeric readout
system, and 0 to 9.9 times continuous sweep delay. A VARIABLE control allows continuously variable sweep rates between
calibrated steps. Also, when operating in the AUTO l\,1AlN TRIGGERING lVlODE, a bright base line is displayed in the
ab,sence of a trigger signal.
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fhe 7892 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 7892. 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 SLOPE. Permits triggering on the positive or negative-
going portion of the trigger signal in all positions oI the
lVlAlN TRIGGERING MODE switch except HF SYNC.
lnstallation
Ihe 7 892 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
slr'Jeep 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 lvlanual. The. instructions in this
manual are written for use of the 7892 in the horizontal
pluq-in compartment. MODE. Four pushbutton s/vitches to select the desired
triggering mode. Selected mode is indicated bV lighted
pushbutton.
CONTROLS AND CONNECTOBS
General
TRIG'D Light. lndicates that the $ueep
will produce a display with the correct
POSITION control and the controls of
vertical units and oscilloscope.
is triggered and
setting of the
the associated
All controls required for the operation oI the '1892,
except the Variable Time/Division Selector and N4ainframe
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 briel description of the front-panel controls
and connectors is given here. l\4ore detailed information is
given in the 7892 Operators Manual. Fig.'l'2 shows the
,ront panel controls and connectors oI the 7892.
Main Triggering Controls
AUTO. Triggered weep is initiated by the applied
trigger signal at a point selected by the LEVEL control
and SLOPE svr'itch when the trigger signal repetition rate
is above 30 hertz and within the frequency ranqe
selected by the COUPLING switch. The srveep 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 sv'/itch, 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 slvitch. Stable displays
can be obtained when the LEVEL control adjusts the
frequency oi the trigger generator to the frequency (or
subharmonic) of the trigger signal frequency. When the
LEVEL control is adjusted to frequencies between
subharmonics, the sr'r'eep free runs.
NORN,4. 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
sv,/itch. Triggered weep 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 wuitch, or the trigger signal
is inadequate, there is no trace.
t-1
section 1-7892 Service
OPERATING INFORMATION
Before proceeding with installation, check the settings of
the Variable Selector multi pin connector and the lMain-
frame Selector multi-pin connector (see Fig. 1'l). The
Variable Selector determines whether the front-panel
VARIABLE control operates in c!niunction with the
Delaying or Delayed Sweep. The lvlainframe Selector
determines the oscilloscope in which the 7892 is to be
operated; any 7900-Series Oscilloscope, or any other
7000"5eries Oscilloscope.
LEVEL. Selects the amplitude point on the trigger signal
where svr/eep triggering occurs when operating in the
AUTO. NORlvl, or SINGLE SWEEP I\,1AlN TRIGGERING
[.4ODE. When operatinq in the HF SYNC l\lAlN TRIG-
GE R ING MODE, the LEVEL controladjusts the frequency
of the trigger generator to synchronize with the trigoering
signal to provide a stable display-
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Operating lnlormation-7892 Service
P309
Tgocseries
Mainlrame
P3m
SINGLE SWEEP-READY. After a s1^,/eep is dis-
played, further $veeps cannot be presented until the
RESET button is pressed. Display is triggered as for
NORM operation, using the MAIN TR IGGERING con
trols. The SINGLE SWEEP-REAOY liqht is illuminated
when the RESET pushbutton is pressed, and remains on
until a trigger is received and the $veep is completed.
MAINFRAME SELECTOR
All oth.r
T00o,series
oscil loscop€s
P309
P30a
VARIABLE SELECTOR
Oelayed Sweep
Variable
(Pin 'l to
rear oI instrument)
Delaying Sweep
Variable
Fig. l-1. Location o, Variable Selector and Mainlrame Selector multi-pin connsctors.
RESET. When the RESET pushbutton is pressed
{SINGLE SWEEP IMODE), a single display is presented
(with proper triggering) when the next trigger pulse is
receivd. The SINGLE SWEEP READY light remains
on until a trigger is received and the srreep is completed.
The RESET pushbutton must be press€d again before
another $/!r'eep can be presented.
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COUPLING. Four pushbutton
coupling. Selected coupling is
button.
Fi9. 1 2. Front panel controls and connecrors
select trigger
lighted push-
svu itches to
ind icated by
AC. Rejects DC and attenuates AC signals below
about 30 hertz. Accepts signals between 30 hertz and
500 megahertz.
AC LF REJ. Rejects DC and attenuates signals below
about 30 kilohertz. Accepts signals between 30 kilohertz
and 500 megahertz.
AC HF REJ. Rejects DC and attenuates signals above
50 kilohertz. Accepts signals from 30 hertz to 50
kilohertz
SOURCE. Four pushbutton $vitches that select the trig-
gering source. Selected source is indicated by lighted
pushbutton.
lNT. Trigger signal obtained internally from vertical
unit bV way of associated oscilloscope.
LINE. Trigger signal obtained internally from a
sample of the line voltage applied to the associated
oscilloscope.
EXT. Trigger signal obtained from an external signal
applied to rhe N4AIN TRIG lN connector.
EXT- 10. Trigger signal obtained from an external
signal applied to the lvlAlN lN connector. ln this
position the external signal is attenuated 10 times before
it is applied to the trigger circuit.
Operating I nf ormation-7892 Service
MAIN
TRIGGERING
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DC. Accepts all signals from DC to 500 megahertz.
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Operating I nformation-7892 Service
Sweep Controls
TIME/DlV OR DLY TIME. Selects the basic svveep rate
for Normal and ALT Sweep operation and selects the delay
time (to be multiplied by the DELAY TIME NiIULT dial
setting) when operating in the INTEN or DLY'D Sweep
mode (see Fiq. 1'3). The VARIABLE control must be in
the CAL position for the indicated sMueep rate.
DLY'D Time/Division- Selects the sv,r/eep rate of the
delayed sweep generator for operation in the DLY'D
Sweep, INTEN, and ALT Sweep Display l\,4odes (see
Fig. 1-3). The VARIABLE control must be in the CAL
position for ind icating the sweep rate.
VARIABLE. Two'position s\r'\iitch actuated by the
VARIABLE control to select calibrated or uncalibrated
slrveep rates (see Fiq. 1.3). ln the CAL position (pressed in)
the VAR IABLE control is inoperative and the sweep rate is
calibrated. When pressed and released, the knob moves out
to activate the VARIABLE control for uncalibrated s1/eep
rates. The slrueep rate in each TIME/DIV svvitch position
can be reduced at least to the saveep rate of the next slower
position. The VARIABLE control can be savitched to
operate with either the delaying or delayed s!,,/eeps by
means ol the internal Variable Selector multi-pin con'
nector.
Display Modes. Four display modes can be selected by
the following $r'uitch settingsl
NORMAL Sweep. A Normal Sweep (non-delayed) is
selected when the TlNilE/DlV OB DLY TIME switch and
the DLY'D Time/Division switch are locked together at
the same sweep rate (see Fig. 13). The DLY'D Time/
Division svritch and the Delayed Triggering LEVEL
control must be pressed in for the Normal Sweep lvlode.
Calibrated sweep rates from 0.2 second/division to 0.5
nanosecond/division can be obtained.
DLY'D Sweep. The DLY'D Sweep Display l\,{ode is
selected when the DLY'D Time/Division switch is pulled
out. rotated in the INTEN Display l\4ode for the desired
delayed sreep rate, then pushed in (see Fig. 1-3). ln this
Display Mode, the delayed sweep is displayed, at a rate
determined by the DLY'D Time/Division $/uitch, at the
end ol each delay period, as selected by the TIME/DlV
OR DLY TltvlE slvitch and the DELAY TllVlE I\IULT
dial settings.
ALT Sweep. When the ALT switch is pressed and
released to the OUT position, svrieeps from both the
delaying slveep generator (intensified slveep) and de
layed srueep generator (delayd sir/,ueep) are displayed.
W$rP vAslastr lcal lt{,
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TIME/DIV OR
DLY TIME
Brack€t enclose normal sweep rate or
delay time (depending upon Display
Mode).
DLY'D Time/Division
Switch
Selects NORMAL Sweep, INTEN, and
DLY'D Sweep Display Modes.
Varies delaying siwe€p rates (INTEN and
ALT Display Modes) or delayed sweep
rates (NORMAL OLY'D and ALT Sweep
Display Modes); dep€nding upon the
connection of rhe Variable Selector
multi-pin connecto. P11o.
VARIABLE Control
1-4 (Al
in Et
INTEN. The INTEN mode, a function of the
delaying and delayed svueeps is selected when the DLY'D
Time/Division switch is pulled out and rotated clockwise
(see Fig. 1-3). ln this mode, a portion of the delaying
sweep is intensified during the time that the delayed
s\tueep generator runs.
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Fig. 1 3. Composite Time/Division switch.
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The alternate sv/eep switches between generators at the
end of each sileeep. The TRACE SEP control is activated
in this Display Mode.
TRACE SEP. When the ALT swilch is OUT (ALT
Sweep Display N4ode), 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 $,veep
generator.
DELAY TIME MULT. Provides variable delay ot 0 to
9.9 times the basic delay time selected by the TllvlE/DlV
OR DLY TlN,4 E $/iitch.
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 {or differences in inpul sensitivity
when changing oscilloscopes.
Delayed Triggering Controls
LEVEL. Control determines delayed s1,^/eep mode, de-
layed trigger mode and delayed trigger level.
IN-RUNS AFTER DLY TIME. The delayed sweep
runs immediately following the delay time selected by
TIME/DIV OR DLY TIME switch and the DELAY
TlN,{E MULT dial. Delayed SLOPE, COUPLIN G, SOU RCE,
and H F SYNC functions are inoperative.
OUT'DLY'D SWP TRIGGERABLE. When the De-
layed Triqqering LEVEL control is pressed and released,
the delayed stueep is triggerable. The Delayed Triggering
LEVEL control can now be rotated to select the
amplitude point on the trigger signal at which the
delayed $veep is triggered, or it can be rotated counter-
clockwise (as marked on the instrument lront panel) to
select the HF SYNC Delayed Triggering Mode. In the
OUT-DLY'D SWP TRIGGERABLE mode, the delayed
SLOPE, COUPLING, and SOUBCE 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'DLY'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
100 megahertz and within the range selected by the
COUPLING s{/itch. 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 which starts the delayed sra,i eep.
-. The delayed svueep can be triggered from the
negative slope of the trigger signal.
COUPLING. Two-position sivuitch 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 l\,4egahertz
SOURCE. Two-position su/itch that selects the source of
the delayed trigger signal.
Front-Panel lnputs
MAIN TRIG lN. When the SOURCE s1r/itch 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 lN. When the Delayed Triggering
SOURCE switch is set to EXT, this connector serves as an
external trigger input for the delayed triggering circuit.
o) 1-5
INTENSITY. Controls the intensity of the delaying
s'w/eep display only. when operating in the INTEN or ALT
Sweep Display lModes.
Operating I nformation-7892 Service
+. The delayed s/!r'eep can be triggered from the
positive slope of the trigger signal.
lNT. The delayed trigger signal is obtained from the
vertical amplifier unit by way of the associated oscillo-
scope.
EXT. The delayed trigger signal ls obtained from an
external signal applied to the DLY'D TRIG lN con-
nector.
TERIVI 50 Q 1 IvlS). Two position switch to select
50ohm or one megohm input impedance for the lvlAlN
TRIG IN and DLY'D TRIG lN connectors.
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CIRCUIT DESCR!PTION
The Iollowing discussion is provided to aid in understanding the overall concept of the 7892. A basic block diagram of the
7892 is shown in Fig. 2-1. Only the basic interconnections betriveen the individual 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 l\4ain Trigger Generator includes circuitry for
selecting trigger source, type of coupling, triggering mode.
and point on the trigger signal where triggering occurs.
Also, regardless o{ the trigger signal, shape. or amplitude
(within specilication) the l\4ain 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 strreep. This gate is also
coupled to the Aux Sweep Gate connector and to Display
Mode Switching for Alternate Sweep operation.
The delaying $veep sa!\,/tooth 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 qate duration; the rate of
change of the sawtooth is set by Ct and Rt. selected by the
TIME/DIV OR DLY TIME switch. The delaving sl/eep
sau,/tooth 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 oI the Delaying Sweep Stop Comparator is
driven by the delaying s1/r'eep 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 adiustment the output of the
comparator $yitches to a positive level.
The positive level Irom the s,rveep stop comparator
initiates the positive holdoff gate. The duration of the
holdof, gate is variable, depending on the setting of the
TIMEiDIV savitch. Holdoff timing capacitors are separare
from sweep timing capacitors, Holdoff is longer for slower
slveep rates. Output lrom the delaying slveep holdotf is
coupled to the l\4ain Trigger Generator. the Delayed Trigger
Generator, aM the Holdorf out connector. A sweep gate
cannot be generated during the holdolf interval. When the
holdoff falls, the trigger circuirs are reset so that they are
ready to receive a trigger signal.
The Horizontal Output amplifier provides positioning
ard amplification of the sawtooth signals. Display l\4ode
Switching works in coniunction with the Horizontal Output
to provide NOBMAL Sweep, INTEN, OLY'D Sweep and
ALT Sweep Display Modes.
The Delay Pickoff circuits produce a delay gate wheo
the delaying sawtooth signal passes through the LEVEL
selected by the DELAY TIME IVIULT dial. The gate ends
with the delaying sa,tooth signal. The output gate is
coupled to the Delayed Trigger Generator.
The Delayed Trigger Gene.ator includes circuitry for
selecting delay€d $/eep mode. delayed trigger mode,
delayed trigger source, type o, coupling, aM the point on
the trigger signal where $!eep triggering occurs. When the
Oelayed Trigger LEVEL is at the RUNS AFTER DLY
TIM E detent, the output s1/\,,eep 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 DLY'D
SWP TFIGGERABLE position, the output trigger is
initiated by the next input trigger signal after the delay gate
is applied. The delayed srreep trigger is terminated by the
h6iii6Ti 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 s,weep. The delayed sl,/eep gate
signal is also coupled to the Sweep Gate Generator.
The delayed s,r,/eep sa/vtooth 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 DLY'D TIME/DlV s,witch.
The delayed sawtooth output is coupled to the Horizontal
Output Amplifier ard the Delayed Sweep Stop
Comparator.
@2-1
Section 2-7892 Service
The Lockout Amp processes mainframe logic signals
(when operating the mainlrame in the aiternate or delaying
Horizontal Modes) to provide a su/eep disable pulse to the
l\4ain Trigger Generator.
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Circu it Description-7B92 Service
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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 voltaqe set
by the Delayed Sweep Length Adjustment, the comparator
slvitches to a positive level. This positive level is coupled to
the Sweep Gate Generator.
Circuit Description-7892 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 (whichever occurs first).
2-3
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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 7Bg2 is not in use, it
should be stored in a protected location. such as a
dust-tight cabinet.
cauTrox-l
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.
Section 3-7B92 Service
MAINTENAN C E
This section ol the manual contains maintenance information for use in preventive maintenance, corrective maintenance,
and troubleshooting ot the 7892.
PREVENTIVE MAINTENANCE 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 ts useful for
cleaning in narrow spaces.
Visual lnspection
fhe 7 892 should be inspected occasionally for such
defects as broken connections, broken or damaged circuit
boards, improperly seatd transistors or relays, and heat,
damaged parts.
The corrective procedure for most visible defects is
obvious; however, particular care must be taken iJ heat-
dam{ed components are lound. Overheatinq usuallv
indicates other trouble in the instrumenu therefore, it is
important that the cause of overheating be corrected to
prevent recurrence of the damage.
Semiconductor Checks
Periodic checks ol the transistors, FET's. and lC'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.
Recalibration
To ensure accurate measurements, check the calibration
of this instrument each 1000 hours of operation or every
six months if used infrequently. ln addition, replacement of
components may necessitate recalibration of the affected
circuits. Calibration instructions are given in Section 4.
TBOUBL ESHOOTING
lntroduction
The following information is provided to lacilitate
troubleshooting ol the 7892. lnformation contained in
other sections of this manual should be used along with the
following information to aid in locating the delective
component. An understanding of the circuit operation is
very helpful in locating troubles. See rhe Circuit Descrip,
tion section.
3"1
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 oI this instrument.
The severity of the environment to which the 7Bg2 is
subjected determines the frequency o, maintenance. A
convenient time to perform preventive maintenance is
preceding recalibration of the instrument,
Cleaning
fhe 7 B92 should be cleaned as olten 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. lt may also provide an electrical
^ conduction path.
lnterior. Dust in the interior of the instrument should
be removed occasionally, due to its electrical conductivity
under high'humidity conditions. The be$ way to clean the
interior is to blow oIt the accumulated dust with dry
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Maintenance-7B92 Service
Troubleshooting Aids
Diagrams. Circuit diagrams are given on foldout pages in
Section 6. The component number and electrical value of
each component in this instrument is shown on the
diagrams.
Circuit Boards. Fig. 6'2 (located in the diagrams
section) shows the location of the circuit boards within this
instrument along with the assembly numbers. The assembly
numbers are used on the diagrams to aid in locating the
boards. Pictures of the circuit boards are shown in the
Diagrams section, on the back of the page opposite the
circuit diagram, to aid in cross re{erencing between the
diagrams and the circuit-board pictures. Each electrical
component on 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 ldentification. Switch cam numbers shown
on the diagrams indicate the position of the cam in the
complete switch assembly. The switch cams are numbered
from front to rear.
Diode Color Code. The cathode end of each glass
encased diode is identified by a stripe, a series ol stripes, or
a dot. For most silicon or germanium diodes with a series of
stripes, the color code also indicates the type ol diode or
identilies the Tektronix Part Number using the resistor
color-code system (e.9., a diode color coded blue-or
pink brown-gray-green indicates Tektronix Part Number
152-0185-00). The cathode and anode ends of a metal
encased diode can be identified by the diode symbol
marked on the body.
Wiring Color Code and Multi-Connector ldenti-
fication. lnsulated wire and cable used in the 7892 is color
coded to aid circuir tracing. lVulti connector holders are
keyed with two triangles (or a triangle and a dot), one on
the connector holder and one on the circuit board. The
triangle on the multi-connector holder must match with the
triangle on the circuit board lor normal circuit operation-
ln special cases where multi'connector holders are used as a
switch. the triangles may not match (see Operaling lnstruc-
tions for special multi-connector holder Iunctions). The
color of the multi-connector holder corresponds to the last
numeral of the circuit number, using the EIA color code
(e.9., P22 is red ).
lnterface Connectoj Pin Locations, The lnterface circuit
board couples the 7892 to the associated oscilloscope. Fig.
3-'l illustrates the locations of pins on the interface
connector as shown on the Voltage Distribution and
Output Connectors schematic in the diagrams section.
Troubleshooting Equipment
The lollowing equipment is useful for troubleshooting
the 7 892.
1. Transistor Tester
Description: Tektronix lype 517 Transistor-Curve
Tracer or a 7CT1N Curve Tracer plug.in unit and a
7000 Series Oscilloscope system.
Purpose: To tefi semiconductors used in this instru-
ment.
2. Volt-ohmmeter
Description: 20,000 ohms/volt. 0-500 volts DC
Accurate within 3%
Purpose: To measure voltaqes and resistance
3. Test Oscilloscope
Description: DC to 100 megahertz frequency response,
five millivolts to five volts/division. Use a 10X probe.
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 the oscilloscope for better
access during troubleshooting.
(4)
3.2
Fi9.3.1. Location ot pins on lnterface connector.
Purpose: To check the waveforms in the instrument.
B
1,.--r'
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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 troub leshooting. The first few
checks ensure proper connection, operation, and calibra-
tion. lf the trouble is not located by these checks, the
remaining steps aid in locating the defective component.
When the defective component is located, it sttould be
replaced following the replacement procedures given under
Corrective l\,{aintenance.
1. Check Control Settings. lncorrect control settings
can indicate a trouble that does not exist. lf there is any
question about the correct function or operation of any
control, see the Operating lnstrLlctions.
2. Check Associated Equipment. Before proceeding
with troubleshooting of the 7B92, check that the equip-
ment used with this instrument is operating correctly.
Check that the siqnal 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). lf the trouble persists after substitution, the oscillo,
scope or vertical plug-in unit should be checked.
3. Check lnstrument 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 trout,les
can be located by visual indications such as unsoldered
connections. broken wires, damaged c!mponents, etc.
5. lsolate 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 INT
position of the SOURCE switch and cannot be obtained in
the EXT or LINE positions, the External Trigger Preamp ar
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 detective
circuit has been located, proceed with steps 6 and 7 to
locate the defective component(sl.
fUaintenance-7B92 Service
6. Check lndividual 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 disconnectirig one eM. 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. lf
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 $tre that
circuit conditions are not such that a replacement
transistor might also be damaged. lf substitute transis,
tors are not available, use a dynamic tester (such as a
Tektronix Type 577 or TCTIN Curve Tracer plug-in unit
and a 7000-Series Oscilloscope system.
c. lntegrated Circuits. lntegrated 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- Be 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.
CAUTION
L.-;
Do not use an ohmmeter scale that has a high internal
current. High currents may damage the diode.
e. Besistors. 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. lnductors. Check Ior 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 olten reduces
high-frequency response.
(4,1 3.3
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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 Readiust the Circuit. lf any defective
parts are locatd, follow the replacement procedures given
in this sedion. Be sure to check the performance of any
circuit that has been repaired, or that has had any electrical
comPonents replacd.
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
7 892 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, lnc. 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
rcmember that the physical size and shape of a
component may affect the Wrformance in the instru'
ment, particularly at high frequencies. All replace'
ment parts sllould be direct replacements unless it is
known that a different component will not adve$ely
affect instrument performance.
When ordering replacement parts from Tektronix, lnc.,
include the following information.
1. lnslrument Type.
2. lnstrument Serial Number
3. A description of the part (if electrical, include circuit
number).
WARIY'IVG
Disconnect the equipment from the pofi,er source
befo re replacing co m ponen ts.
Relay Replacement. The relay in the 7892 is manu-
factured by Tektronix, lnc. lf the relay fails, a replacement
mav 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. Sem imnd uctor devices
used in this instrument should not be replaced unless
actually defective. lf removed from their sockets during
routine maintenance. return them to their original sockets.
Unnecessary replacement may aflect the calibration ol this
anstrument. When a semiconductor is replaced, check the
operation of the part of the instrument that may be
affected.
Replacement devices should be ot the original type or
direct replacement. Re-install in the same manner as the
original. Fig. 6-l (located in diagrams seclion) shows the
lead configurations of the semiconductor devices used in
this instrument. When replacing, check the manufacturer's
basing diagram for correct basing.
lnterconnecting Pin Replacement. Two methods of
interconnection are used in this instrument to conned 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- lf the mating connector is mounted
on a plug-on circuit board. a special socket is soldered into
the board. l, 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 tor the various interconnecting
methods.
Coaxial Type E nd-Lead Connectorsa
Replacement of the coaxial type end-lead connectors
requires special tools and techniques; only experienced
maintenance personnel should attempt replacement of
these connectors. lt is recommended that the cable or
wiring harness be replaced as a unit. For cable or wiring
harness part numbers, see the l\,4echanical Parts List. An
alternate solution is to refer the replacement of the
delective connector to your Tektronix Field Ofrice or
rePresentative.
Component Replacement
3-4
4. Tektronix Part Number.
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b. Circuit Boa!'d Pins and Pin Sockets.
\ cAUTrOrV
)(
The following procedures are recommended for
singleJayer circuit boards only. Pin and socket
replacement on multi-layer circuit boards should be
performed only by specialized *rvice personnel.
Refer to your local Tektonix Field Office or Service
Center.
A circuit board pin replacement kit including neces-
sary tools, instructions. and replacement pins is available
from Tektronix, lnc. (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 oI 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 neu,i
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. lf the old pin was bent at an angle to mate
with a connector, bend the new pin to match the
associatd 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 carelul not to get
solder into the socket
Maintenance-7892 Service
NOTE
The spring tension of the pin eckets 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 springloaded probe
tips, alligator clips, 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 oI the pin connectors are grouped together and
mounted in a plastic holder; the overall result is that
these connectors are remorred 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 oI the multi-pin
connector. Be sure that these arrows are aligned when
the multi-pin connector is replaced. lf the individual
end.lead pin connectors are removd trom the plastic
holder, note the color oI the individual wires for
rePlacement.
Switch Replacement. Pushbutton s\,vitches ard a cam,
type sv,/itch are used in the 7892. lt is recommended that
both slvitch types be replaced as a unit. Refer to Fig. 3,2
for cam-svt/itch removal and to Fig. 3-3 for pushbutton
savitch removal.
(, 3-5
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Maintenance-7892 Service
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CAUTION
OO NOT REMOVE
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Fig.3-2. Cam switch removal
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