TM 11-6625-486-14&P
circuit board (fig. FO-2 (1) and FO-3 (1) ). Crystal Y202
from the front section of S703 to the mixer circuit board.
is the 1-MHz crystal, and Y201 is the 2.5-MHz crystal.
Unsolder this resistor from S703.
side panel and mixer circuit board. Leave the mixer
(2), all replaceable parts can be replaced without
board hanging on its leads and remove the side panel
removal of the unit. All parts have voltage and current
entirely.
ratings 'far in excess or normal operating conditions and
should last beyond the life of this instrument. The vfo,
g. The two switch-mounting brackets are secured
tuning capacitor, and mechanical drive system are
to the chassis with four screws and nuts. Loosen the
integrated into one unit and, if disassembled, will void
front bracket by taking out the two screws and nuts.
the entire calibration of the unit. If new parts are
Remove the screws and nuts from the rear bracket. To
installed in the same physical location and with the
facilitate removal, loosen the screws from under the
same lead lengths as the original part, calibration should
chassis until the nuts can be removed. Switch S703 can
not be affected.
then be moved forward a small amount for access to the
wiring.
The two dial lamps (fig. 6-1, 6-12, and 6-13) are
mounted on an L-shaped bracket that is attached to the
section of S703. Refer to the wiring diagram (fig. FO-6
film mask with two screws and associated nuts. The
or FO-7) and tag or mark each wire as soon as it is
lamps receive power through a shielded cable
removed.
connected to the modulator circuit board. Install a new
i. Carefully unsolder the wiring on the rear section
lamp as described below.
of S703. Tag or mark the wires. Be extremely careful
a. Pull the battery drawer out of the front panel.
not to damage trimmer capacitors C112 and C114.
Remove switch S703.
j. Remove the mounting brackets from the
defective switch and remount them on the new switch.
attached to the mechanism frame with a screw and nut
k. Reconnect and solder the wires on the rear
section of the new switch. Install the screws and nuts on
c. Note that the dial lamp mounting bracket is
the front and rear switch mounting brackets. Reconnect
attached to the mask with two screws and nuts (fig. 6-
and solder the wires on the front section of S703.
l. On the shaft of S703, remount the filmstrip
bracket upward and pull it out through the side of the
mask operating lever and block with the screw and nut.
film mechanism frame.
Attach the lever to the filmstrip mask (fig. 6-12).
d. The wire leads of the lamps are soldered to
m. With the four screws and nuts, remount the
terminals on an insulated board. If not sure which lamp
mixer circuit board on the right side panel. Replace the
is defective, plug the power cable into the front panel ac
side panel with the six screws. In the AN/USM-169 only,
receptacle and source of ac power.
Turn the
resolder the 10K resistor (R108) onto switch S703.
FUNCTION SW to OPER and note which lamp does not
n. Replace the front panel and remount the battery
glow. Unsolder the defective lamp and replace it with a
drawer support bracket. Slide the battery drawer in
new type NE-2 lamp. If the lamp still does not glow, turn
place.
off the power and check the associated current limiting
o. Reconnect and solder the wires on battery
resistor.
interlock switch S702, voltmeter M701, and the ANT.
jack. Replace the panel control knobs.
e. Remount the dial lamp mounting bracket and
secure it to the mask with the two screws and nuts.
6-22. Removal and Replacement of Other
Replace the lamp cable clamp and film mechanism top
Components
cover. Replace the battery drawer.
a. The PHONES jacks, AUDIO GAIN control,
function switch, fuse posts, and ac receptacle can easily
be reached from underneath the chassis (fig. 6-5 and 6-
Mechanism and Filmstrip
6) and replaced in accordance with general repair
a. Removing Filmstrip Mechanism.
practice. The only precaution that need be observed is
to tag each wire as soon as it is removed to avoid
(1) On the modulator circuit board, unsolder
misconnection when installing the new part. The 1-MHz
and 2.5-MHz crystals are secured to their sockets with
spring clips on the crystal oscillator and modulator
6-22
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