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Tektronix T922R
Service Notes

The Tektronix
T922R oscilloscope was discontinued in the middle 1980s;
Tektronix ended long term support in 1995.  Tektronix no
longer stocks parts unique to the T900 Series scopes.
Nevertheless, the T922R remains in daily use in wireline
logging trucks all over the world.  This page contains
some random notes on servicing these old
workhorses.

Old Tektronix manuals are truly works of
art.  Reading the manual and studying the schematics is
an education in and of itself.  The T921/T922/T922R
manual is a combined operating and service document.  We
have accumulated a few extra manuals for the T921/T922/T922R
scopes.  If you need one, tell us about yourself and we
might make you the proud owner of one of our extra
manuals.  If you need to troubleshoot a T922R, start with
the flow chart on pages 5-4 and 5-5 of the
manual.

If the oscilloscope is completely dead, of
course first check the fuses.  T922Rs have been known to
blow fuses when turned on in cold weather.  F722, a 1/16
amp slow blow fuse in the 100 volt power supply circuit, has a
habit of blowing if the line voltage goes high (as in
generator runaway). The power indicator pilot lamp on the
T922R flashes if the line power varies more than 10% above or
below the value for which the internal power selection
switches are set.  T922Rs below serial number B011950
have a neon power indicator pilot lamp, and those with serial
number B011950 and up have an LED power indicator.  Some
of the T900 Series did not work well with 50 Hz line power;
the power transformer core saturates and radiates 50 Hz noise
into other parts of the scope circuitry.  A mu-metal
shield for the transformer cures the problem.  The extent
to which this problem specifically occurs in the T922R is not
well documented.

As with all
electronic equipment, component failures are increasing as the
T900 Series oscilloscopes age.  The filter capacitors on
the power supply board are now prone to failure; look at C742
and C743, both 2,200µf at 16 volt electrolytics, and C722, a
100µf at 160 volt electrolytic.  VR4367, a 4.3 volt, 0.4
watt zener diode on the vertical board, causes a no trigger
condition when it fails.  Problems have been reported
with the various interconnect cables.  Check all internal
wiring for bad connections at the various connectors.
The scale illumination bulbs, DS816 and DS818 can be replaced
with a 1764 lamp, but the 2187 is rated at 7,000 hours as
opposed to the 1764's 4,000 hours with only about a 10%
decrease in light output (if you can stand a 40% reduction in
light output, the 2185 is rated at 50,000 hours).  Shorts
or opens are sometimes seen in the high voltage tripler
assembly (U460).  These are potted assemblies not
intended to be repaired at the component level.  At
present there is no known source of replacement tripler
assemblies, except from scrapped instruments.  Stan Griffiths, scope
guru, has indicated he is looking for a solution to this
problem; visit Stan's Scope
Site, and the Tektronix
Resource Site which he
co-created.

The .022µf, 400 volt vertical input coupling
capacitors (C4102 and C4202) sometimes go open or short
out.  If your T922R works when connected to a panel
equipped with its own scope output coupling capacitor (SIE
bond panels, for instance), but misbehaves when connected
directly to the line, suspect a shorted C4102.  The
vertical input dual JFET transistors (Q4122 and Q4222) fail
occasionally.  They can be replaced with an ECG/NTE
461.  These two problems with the vertical input are
often caused by exceeding the rated input
voltage.

The T922R cam switches frequently give
problems.  It is not uncommon to find dead positions in
one of the "VOLTS/DIV" switches located on the vertical
attenuator boards, or in the "SEC/DIV" switch located on the
horizontal board.  A very dirty vertical attenuator cam
switch can cause an erratic display in all positions.
Reassembly of cam switches is a nightmare, so cleaning is
usually attempted first.  Only a residue free cleaner
should be used, and one that will not attack the plastic parts
in the switch.  Do not lubricate the switch contacts (no
WD-40 or the like).  Tektronix recommends plain old
isopropyl alcohol.  We have had good luck with Caig Laboratories'
DeoxIT cleaner.

Check out Cleaning
Secrets Revealed for some tips on how to make your scope
look like new.  The plastic polishing technique outlined
near the bottom of said page is useful for removing scratches
from the CRT implosion shield and/or the face plate (lens or
filter).  Done properly, even a badly scratched face
plate can be made to look like new.

Below is a cross
reference list of some of the T922R semiconductors.

T922R Tektronix to
Generic Semiconductor Cross Reference

TEK PART NO  GENERIC  TEK SCHEMATIC DEVICE
LABELS

151-0126-00  2N2484   Q446
151-0127-00
2N2369   Q134
Q136 Q144 Q146
151-0188-00  2N3906
Q166 Q446 Q454
Q2108 Q2124 Q2134 Q2136 Q2174 Q2176

Q2326
Q2332

151-0190-05  2N3904   Q160 Q162 Q416 Q424 Q810 Q2246 Q2274
Q2314 Q2354

Q2422 Q2432
151-0192-03  MPS6521
Q2314
151-0199-00
2N3640   Q112
Q122 Q4174 Q4176 Q4274 Q4276 Q4302 Q4303 Q4310

Q4311 Q4312 Q4313 Q4322
Q4324 Q4336 Q4346
151-0216-02  MPS6523
Q2176
151-0223-03
2N5769   Q2412 Q4372
151-0224-00  2N3904
Q792

151-0301-00  2N2907A  Q772 Q774
151-0302-00
2N2222A  Q752
Q754

151-0347-00  2N5551   Q426 Q722 Q726 Q734 Q796 Q818 Q2334
Q2344

151-0350-00  2N5401   Q434
151-0358-00
D44R4    Q458

151-0423-00  TIP50    Q458
151-0434-01
2N4261   Q4322 Q4324
151-0478-00  TIP31A
Q756
Q776

151-0497-00  TIP47    Q736 Q812 Q816
151-1042-00
2N5454   Q2104 (Q2106) Q2114 Q2242
151-1090-00
D/2N5397 Q4122 Q4222
(Use
ECG/NTE461)

156-0197-03  LM3086   U2126 U4134 U4234
156-0405-02
N9602N/F U2224

Note:  A suffix other than
"00" indicates a selected transistor.

If you need more information or are working
on other Tek equipment, the Tektronix
Resource Site has an amazing Tektronix
to Generic Transistor Type Cross Reference.
Sphere also
has a semiconductor cross reference, and other useful
stuff.
Much of the above was inspired by Paul Knight, our logging
equipment repair guru.

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Tek
and Tektronix are registered trademarks of Tektronix, Inc.
Manual
background used with the kind permission of the Tektronix
Resource Site.
03-05-01
Last 10-15-01