Tektronix 442, Инструкция по эксплуатации

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Maintenance—442 Service
Cam Switch Repair and Replacement
A cam switch is an assembly consisting of a cam
rotated by afront panel control, and a set of contacts on an
adjacent circuit board.
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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 that
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 use any cleaners that 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 (such as a cotton swab) that
could snag the contact.
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. While this may tem­
porarily fix the problem, 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 the area of the contact
while operating the switch.
3. Flush the contact with isopropyl alcohol and blow it
dry with low-pressure air. Isopropyl alcohol flammable;
avoid its use near open flame or other potential sources of
ignition.
If the above procedures don’t work, replacethe contact
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 Replaceable Mechanical Parts list for ordering infor­
mation.
If a replacement contact stripassemblyis not available,
bend the contact for a temporary repair. If a contact must
be bent, note its location and the symptom that required
the bending, for reference if the contact fails again before
a permanent repair can be made.
A6 and A7 Attenuator Removal
The following procedure is valid for removing the
attenuator assembly for either channel. Place the instru­
ment in the position shown in Figure 5-8 (temporarily
reassemble the rear cabinet frame and four feet to the rear
panel with the Phillips-head foot securing screws to
support the 442).
NOTE
The attenuator assemblies may be removed before
the A8 Vertical board is removed. However, the
Vertical board may be removed without removing
the attenuator assemblies from it (the VOLTS/DIV
and VOLTS/DIVVAR knobs m ust be removed before
either the attenuator assemblies or the Vertical
board can be removed.
1. Remove the appropriate VOLTS/DIV and VAR
knobs (use a 1/16" Allen wrench).
2. Use a Phillips screwdriver to remove the two
screws that secure the small shield to the
Channel 1 and Channel 2 attenuator shields. Set
the small shield and screws aside.
3. Use a Phillips screwdriver to remove the two
screws that secure the Channel 2 attenuator
shield and the three screws that secure the
Channel 1 shield (one screw head faces the crt
shield).
5-16
REV A MAY 1980