Tektronix 7A26 User manual

040-0785-01
VERTICAL AMPLIFIER MICROCIRCUIT REPLACEMENT
For the following TEKTRONIX ®instruments:
7A26 Serial Numbers BOlOlOO -B139377
This kit provides parts and instructions to replace one of the
vertical amplifier microcircu«‘s. For serial numbers below
B1 10000, the emitter compensation networks for U1750 and
U2750 need to be modified. In order to optimize the lOOHz
to lOOkHz square wave response (low-frequency
compensation) .selection of several components may be
necessary.
Tektronix, Inc. Supersedes: 13-JUL-1979
All Rights Reserved
TEKTRONIX, SCOPE-MOBILE and are registered trademarks of Tektronix, Inc. SONY /TEKTRONIX is aregistered trademark of Sony /Tektronix, Inc.

CAUTION
STATIC SENSITIVE DEVICES
Static discharge can damage any semiconductor component
in this instrument. Static voltages of IkV to 30kV are
common in unprotected environments.
TO AVOID DAMAGE. OBSERVE THE FOLLOWING:
1. Minimize handling of static-sensitive components.
2. Transport and store static-sensitive components or
assemblies in their original containers, on ametal
rail, or on conductive foam. Label any package that
contain^ static-sensitive assemblies or components,
3. Discharge the static voltage from your body by
wearing awrist-strap while handling these
components. Servicing static-sensitive assemblies or
components should be performed only at astatic-free
work station by qualified service personnel.
4. Nothing capable of generating or holding astatic
charge should be allowed on the work station
surface.
5. Keep the component leads shorted together whenever
possible.
6. Pick up components by the body, never by the
leads.
7. Do not slide the components over any surface.
8. Avoid handling components in areas that have afloor
or work-surface covering capable of retaining a
static-charge,
9. Use asoldering iron that is connected to earth
ground.
10.
Use only approved. anti-static type. desoldering
tools.
040-0785-01 page 2

KIT PARTS UST:
Ckt, Number Quantity Part Number
A1ea 155-0078-10
C1/21
C2721 2ea 281-0123-00
R1722
R1724
R2722 4ea 315-0150-00
R2724
1ea
*U1350, U1450, U1550. U1750. U2350
Description
Microcircuit, li. vertical amplifier
Capacitor, var. cer. 5-25pF. lOOV
Resistor, cmpsn. 15n. 5%. 0. 25W
Label. 040-kit
U2450. U2550 or U2750
Fig. 1. Partial -Amplifier circuit board (solder side)
040-0785-01 page 3

INSTRUCTIONS;
WARNING
Before proceeding, ensure the mainframe power
switch is in the off position, then remove the
amplifier plug-in from the mainframe.
()1. Remove the left and right side electrical shields.
NOTE
The emitter compensation networks for U1750
and U2750 were modified at serial number
B1 10000. Steps 2through 16 are instructions
to add this modification to the *7A26.
Therfore. these instructions (steps 2through
16) may be disregarded for amplifiers in
serial number range B1 10000 to B139377 or
in Instruments which have already had this kit
installed.
Steps 2through 8involve the removal of
Cl 721. C2721. R1721 and R2721. These
components were added to the 7A26 at serial
number B050000. Instruments in serial
number range BOlOlOO to B049999 may
disregard steps 2through 8.
()2. Remove the CHI Readout circuit board (A3) mounting screws -one
near the rear and six near the front.
()3. Swing the CHI Readout circuit board out of the way to gain access to
the back of the Amplifier circuit board (A2)
.
()4. Amplifiers in the serial number range B050000 to B109999 only: Cut
and remove the two runs on the back of the Amplifier circuit board
as shown in Fig. 1.
040-0785-01 page A

NOTE
The runs to be removed are located under
the CHI VARIABLE (CAL IN)/ GAIN
potentiometer-switch combination. Removal of
the combination will facilitate access to the
circuit board runs.
Fig. 2. Partial -Amplifier circuit board (component side)
Place the CHI Readout circuit board on the Volts/DIv cam switch
bearings and secure the circuit board with the seven screws removed
above.
I
For steps 6through 15, refer to Fig. 2.
On the front (component) side of the Amplifier circuit board, cut and
remove the run between C2721, a5-25pF variable capacitor, and
R2721, a27n, 0. 25W resistor.
040-0785-01 page 5

Remove C2721 and R272K
Remove Cl 721. a5-25pF variable capacitor, and R1721. a25n.
0.25W resistor, located near U1750,
Unsolder and lift the ends of R1720 and R1723 (both 1.37kn
resistors) which connect to pin 2and 3. respectively, of U1750.
Trim the leads of the four 15n resistors. Included In the kit. to about
3/16 (0. 1875) Inch.
Add R1722 and R1724. two of the 15n resistors. In series between
the lifted ends of R1720/R1723 and the circuit board pads from which
the ends were lifted.
Add Cl 721. one of the 5-25pF variable capacitors included In the kit.
between the junctions of R1720/R1722 and R1723/R1724.
Unsolder and lift the ends of R2720 and R2723 (both l,3kn) nearest
U2750.
Add R2722 and R2724. the two remaining 15n resistors. In series
between the lifted ends of R2720 and R2723 and the circuit board
pads from which the resistors were lifted.
Add C2721. the remaining 5-25pF variable capacitor, between the
junctions of R2720/R2722 and R2723/R2724.
Replace the faulty amplifier microcircuit (U1350. U1450. U1550,
U1750. U2350. U2450. U2550 or U2750) with the microcircuit
provided In the kit.
Refer to the Calibration Section (5) In the 7A26 Instruction Manual
and check instrument performance. making any necessary
adjustments. The attached manual Insert contains supplemental
calibration Information.
NOTE
In order to optimize the lOOHz to lOOkHz
square wave response (low-frequency
compensation) .several components may need
to be selected. If U1350. U1450 or U1550
has been replaced. C1332. R1332. C1431.
R1341 or Cl 436 may need to be selected.
Replacement of U2350. U2450 or U2550 may
require selection of C2332. R2332. C2431.
R2431 or C2436. In some cases, removal of
C2533 may be desirable.
040-0785-01 page 6

()18. Remove the protective backing from the 040-kit label (included in the
kit) and apply It to the top frame section. The label indicates the
installation of this kit for future reference,
()19. Install the electrical shields.
()20. Attach the included manual insert to the Instruction Manual.
REH:rh
040-0785-01 page 7

Product Modification Kit
SUGGESTION/CORRECTIOIM FORM
DATE
KIT NUMBER STEP/PAGE
FIGURE NUMBER PUBLICATION DATE
DISCREPANCY
SUGGESTED CORRECTION /COMMENTS
SUGGESTED BY; NAME /ORGANIZATION
DREPLY REQUESTED
RETURN TO LOCAL FIELD OFFICE /SERVICE CENTER
FIELD OFFICE /SERVICE CENTER /DEL. STA.
SERVICE CENTER: RETURN TO FIELD MODS 73-860
REPLY
im WILL MAKE CHANGE IMMEDIATELY
[H WILL MAKE CHANGE AT NEXT PRINTING
nOTHER
SIGNED DATE

TEKTRONIX
MANUAL MODIFICATION INSERT
VERTICAL AMPLIFIER MICROCIRCUIT REPLACEMENT
for
7A26 Serial Numbers BOlOlOO -B139377
Installed in SN Date
This modification Insert is provided to supplement the manual
for the above listed product(s). The Information given in
this insert supersedes that given in the manual.
Copyright ©1984 by Tektronix. Inc. ,Beaverton. Oregon.
Printed in the United States of America. All rights
reserved. Contents of this insert may not be reproduced in
any form without the permission of the copyright owner.
GENERAL INFORMATION
This kit provided parts and instructions to replace one of the
vertical amplifier microcircuits. For instruments in serial
number range B010100 to B109999. the emitter compensation
networks for U1750 and U2750 were modified.
In order to optimize the lOOHz to lOOkHz square wave
response (low-frequency compensation), several components
may have been selected. For Replacement of U1350. U1450
or U1550. changes in the values of C1332. R1332. C1431.
R1431 or Cl 436 may have been required. Selection of
C2332. R2332. C2431 or C2436 may have been necessary if
U2350. U2450 or U2550 was replaced. In some cases,
removal of C2533 may have been beneficial.
040-0785-01 page 1

REPLACEABLE ELECTRICAL PARTS
CKT. NO.
C1721
C2721
R1721
R1 722
R1724
R2721
R2722
R2724
*U1350,
PART NUMBER DESCRIPTION
Capacitor, var. cer. 5-25pF lOOV
Capacitor, var. cer. 5-25pF lOOV
281-0123-00
281-0123-00
DELETE
315-0150-00
315-0150-00
DELETE
315-0150-00
315-0150-00
155-0078-10
Resistor, cmpsn.
Resistor, cmpsn.
Resistor, cmpsn.
Resistor, cmpsn.
15n 5% 0.25W
15n 5% 0.25W
15n 5% 0.25W
150 5% 0.25W
Microcircuit, linear, vertical amplifier
U1450. U1550. U1750. U2350. U2450. U2550 or U2750
—vw /5
C/7Z/
IZIJZ3
Mp/o
UI750
“AAA/—
/S
Partial -CHI AMPLIFIER schematic
Asimilar schematic applies to
channel 2. The first digit in
each circuit number changes
to 2. e.g. C2721,
040-0785-01 page 2

SECTION 5-CALIBRATION
Replace step 8with the following:
8. CHECK/ADJUST CHANNEL 1AND 2
HIGH FREQUENCY COMPENSATION.
a. Set the CHI and CH2 VOLTS/DIV
switches to lOmV.
b. Connect the Pulse Generator to the
7A26 CH2 input through a5X 50n
attenuator and a50n terminator.
c. Set the time-base unit to obtain a
triggered display at arate of
approximately 0. 2ns per division.
d. Position the top of the waveform to
one division above the center
screen. Note the peak-to-peak
amplitude.
e. CHECK -Aberrations should not
exceed ±4% and 6% peak-to-peak
of the pulse amplitude noted in
part d.
f. ADJUST -High-frequency
compensations C2336, R2336.
C2432 (C1432 and C2432 added at
serial number B083790) .C2435.
R2435, C2531. R2531 ,C2345 and
R2345 for best front corner and
flat top.
9- Remove the 7A26 from the Vertical
compartment and insert the plug-in
extender to the same
compartment
h. Insert the 7A26 into the plug-in
extender.
i. Reverse the trigger cable
connections from All to A13, and
Bll to B13 of the plug-in
extender.
j. CHECK -Aberrations should not
exceed ±10% and 15% peak-to-peak
total of the pulse amplitude.
k. ADJUST -High-frequency
compensation C2721 for minimum
aberrations.
l. Repeat step f.
m. Remove the plug-in extender from the
mainframe vertical compartment and
insert the 7A26 Into the mainframe
vertical plug-in compartment.
n. Disconnect the Pulse Generator from
CH2 and connect to the CHI input
through a5X 50n attenuator and a
50n termination.
o. Set the DISPLAY MODE switch to
CHI.
p. CHECK -Aberrations should not
exceed ±4% and 6% peak-to-peak of
the pulse amplitude.
q. ADJUST -High-frequency
compensations C1336. R1336. C1432
(Cl 432 and C2432 were added at
serial number B083790) .C1435.
R1435. C1531. R1531. C1345 and
R1345 for best front corner and flat
top.
Remove the 7A26 from the vertical
compartment and insert the plug-in
extender Into the compartment.
Insert the 7A26 Into the plug-in
extender.
040-0785-01 page 3

t, CHECK -Aberrations should not
exceed ±10% and 15%
peak-to-peak total of the pulse
amplitude.
u, ADJUST -High-frequency
compensation Cl 721 for minimum
aberrations.
V. Repeat part q.
w. Remove the plug-in extender from
the mainframe vertical compartment
and Insert the 7A26 into the
mainframe vertical compartment.
X. ADJUST -Cl 34 (both channels)
for best compromise between 10.
20 and 50mV positions for first
20nSec of pulse.
y. Disconnect all test equipment.
z. Repeat Channel 1and 2
Low-frequency Compensation check
and adjust.
040-0785-01 page 4