REPAIRS AND ADJUSTMENTS
ment. Reassembly in reverse order of disassembly
Parts Replacement Techniques
AN/GSM-64A, follow the precautions given be-
Although not necessary, it may prove
more convenient to remove the handle
a. Do not disturb the settings of potentiometers
while performing maintenance on the
R1 through R7.
instrument. To do so, turn knobs counter-
b. Before a part is unsoldered, note the position
clockwise until they can be removed from
of the leads. If the part to be replaced has a num-
the chassis frame, and remove handle.
(1) Remove power cord from power outlet.
(2) Turn fuse holder cap counterclockwise
c. Be careful not to damage other leads by pull-
and remove it from the body of the fuse holder.
ing or pushing them out of the way to reach
(3) Remove top and bottom covers by re-
other parts or connections.
moving two screws in each at rear of instru-
Do not allow drops
of solder, loose
ment and moving covers away and back toward
nuts, or washers to fall into the equipment; they
rear of instrument.
may cause short circuits and damage to the in-
(4) Remove top and bottom shields by re-
moving four screws attaching each to standoffs
on the circuit board.
rectly soldered joint is a potential source of
(5) Remove six screws attaching signal con-
trouble and is extremely difficult to find.
ditioning assembly to chassis frame and place
f. When a part is replaced, position it exactly
as the original part. Pay particular attention to
(6) Remove bezel and front panel by re-
proper grounding when replacing a part. Use
moving the four screws attaching bezel to chas-
the same ground as in the original wiring. Failure
to observe these precautions may effect the ac-
(7) Remove polarity and overload lamp bulb
curacy of the instrument.
bracket by removing screw at side of instrument
of Parts in Digital Voltmeter
a. Disassembly. The following steps are pro-
(8) Pull front plate away from chassis by
vided to enable the repairman to disassemble the
removing two screws on each side of plate and
instrument in the easiest manner down to the
by removing nut attaching EXT REF VDC toggle
point where further disassembly, if required, is
switch to front plate.
obvious. It is not necessary to follow all of these
b. Integrated Circuit Replacement.
steps to effect certain repairs or replacements.
(1) Remove power cord from power outlet,
The folIowing paragraphs of this chapter, per-
top cover, and top shield (a(1), a(3), and a(4)
taining to repair or replacement of parts or ad-
justment procedures, will refer to steps in this
paragraph which are required to be taken prior
(2) Place signal conditioning assembly in
to proceeding with repair, replacement or adjust-
upright position (a(5) above).