Tektronix T921 User Manual

Service Information-T921/T922/T922R
NOTE
The
VOL TS/DIV shaft end is molded to form a key
that fits
into the cam . Attempting to force theshaft
into the cam when it is
not properly lined up, will
damage the cam switch .
5 . Line
the VOLTS/DIV knob and shaft up with the cam
and slide into
place . When the shaft and cam are lined up,
the shaft slides
into the cam easily .
6 . Replace the VOLTS/DIV VAR
knob
and
shaft and
tighten the
set screws .
Cam Switch Repair and Replacement
A cam
switch is actually an assembly consisting
of a
cam
rotated by a front panel control and a set of contacts
on an
adjacent circuit board .
Repair of cam switches should
be undertaken only
by experienced repair personnel . Switch
alignment
and
spring tension of the contacts must be
carefully
maintained for
proper operation of the switch . For
assistance in repair
of the cam switches, contact
your local Tektronix Field
Office or representative .
Cleaning . If the
contact is not obviously damaged, try
cleaning it before replacing .
Follow the cleaning
procedures in the order given ;
the first ones are the
easiest .
When cleaning cam switch
contacts :
1 .
Don't use cleaners, detergents, or
lubricants
which
leave a residue . The residue can interfere with
the
high-frequency response of the contact . Also,
the residue
will attract dust and cause the contact to
require frequent
cleaning .
2 .
Don't useany cleaners which contain
fluorocar-
bons .
These will damage the cam portion of the
switch .
Fluorocarbons also damage the circuit
board material used in
some instruments .
3 . Don't
use anything that could snag the contact,
like a cotton
swab .
5- 1 4
4 . Don't scrape the
pad . If the gold is removed from
the pad, the pad will oxidize
and cause future
problems .
5 . Don't bend the contacts . This may temporarily fix
the problem
. However, bending the contact
damages its self-cleaning action
and causes
problems in the future .
Use the
following procedures - to clean the contacts :
1 . Operate the switch several times . The
wiping action
may clean the contacts .
2 . Blow low pressure air in
thearea of the contact while
operating the switch .
3 . Flush
the contact with isopropyl alcohol and blow dry
with low-pressure
air . Isopropyl alochol is flammable ;
avoid its use
near open flame or other potential sources of
ignition .
If the
above procedures don't work, replace thecontact
strip . If
cleaning the switch restores continuity, check to
ensure
that the contact wipes across the pad . If the contact
does not wipe,
replace the contact strip .
Contact Replacement . Cam Switch contacts in
this
instrument are part of a contact strip assembly . Refer
to
the
mechanical parts list for ordering information .
If you do not have a replacement
contact strip
assembly, bend the contact for a temporary
repair
.
If you
do bend
the contact, make note of its location
and the
symptom it
causes . This will speed repair if the contact
fails before youcan make
permanent repair .
Trigger
Switch BoardReplacement
If the
early production TriggerSwitch board is to be
replaced, it
must be replaced with the late production
Trigger Switch
board . In this event, C2123, R2117, R2119,
and R2120 (located
on
the A12
Horizontal board), may be
removed ; they have no effect when the
late production
Trigger Switch board is used . Refer
to
Diagram
5 and
Circuit Description for the late version when the late
production Trigger Switch board is used .
Time Base Replacement
To remove the Time Base from the instrument
:
1 . Remove the Vertical
Amplifier . See Vertical Amplifier
Replacement for instructions .
REV . A, JUNE 1976

Tektronix T921 Specifications

General

Brand	Tektronix
Model	T921
Category	Test Equipment
Language	English