TM 11-6625-486-14&P
NOTE
c. Carefully pull the top of the side panel away
Do not unsolder the wires connected
from the chassis; be careful not to damage the wiring
from terminals 1 and 2 to C112 and
that remains soldered to the mixer circuit board.
C114 at this time.
d. Remove the mixer board by removing the four
c. The coilbox is chassis mounted with four nuts
screws and nuts that hold the board to the side panel.
Any part on the mixer board can now be replaced
pull upward on Z101 and remove the unit.
without unsoldering the main terminal wiring. If the
wiring is handled carefully, voltage and resistance
d. On the coilbox terminals, unsolder the leads
measurements can also be made.
going from terminals 1 and 2 to C112 and C114; then,
e. After the defective part is replaced, mount the
loosen the two nuts and screws that hold the trimmer
capacitor mounting bracket to the coilbox and remove
mixer board on the side panel with the four screws and
the bracket.
nuts; then attach the side panel to the chassis and front
with the eight screws. Solder the 10K resistor to switch
e. Obtain a new coilbox and remount the trimmer
S703, and the antenna lead (bare wire) to the ANT.
capacitor bracket with the two screws and nuts. Solder
jack.
the trimmer capacitor leads on terminals 1 and 2.
f. Mount the coilbox by replacing the four nuts
Vfo Circuit Board
under the frequency meter chassis; then, connect and
The wiring connected to the low frequency vfo circuit
solder the wires on terminals 1 through 5 and the ground
board is too short to permit repairs to be made without
lug.
unsoldering the wires.
and replace the low frequency vfo circuit board.
FO-6 or FO-7 and carefully unsolder the wires
h. The low frequency vfo should then be aligned
connected to circuit board terminals 1 through 7. Note
the wire color and mark or tag the wire for identification.
and given a final test.
b. The vfo circuit board is mounted on coilbox
6-21. Removal and Replacement of Switch S703
Z101 with four nuts (one at each corner of the board).
(RANGE SW)
Remove the four nuts and the board.
c. After repairs are made, remount the circuit
switch S702 and voltmeter M701. Remove these wires
board on Z101 with the four nuts. Resolder the wires on
and tag them for identification; then, unsolder the bare
board terminals 1 through 7. Arrange the wiring in
wire connected to the ANT. jack on the front panel.
approximately the same position as before.
b. With a set of Allen wrenches, remove the front
d. The low frequency vfo should then be given a
panel knobs. Slide the battery drawer out of the panel.
final test to be sure it functions with its original accuracy
c. Remove the two screws and nuts that hold the
battery drawer support bracket to the front panel. The
front panel is held to the left and right side panels by two
Vfo Coilbox Z101
screws that extend through each side panel. Remove
Low frequency vfo coilbox Z101 was sealed during
the four screws and the front panel.
manufacture; no attempt should be made to unseal it. If
the humidity indicator (fig. 6-1) turns pink, or some
d. The mask in the filmstrip mechanism is
internal component is defective, the coilbox must be
mechanically linked with a lever to the shaft of switch
replaced.
S703. Remove the nut and screw that hold this lever to
the film mask (fig. 6-1 and 6-12). The other end of the
lever is mounted on the shaft of S703 with a screw and
following the procedure given in paragraph 6-19, but do
nut attached to a rectangular block. Remove this
not unsolder the wire on terminal 7.
hardware and pull the block and mask operating lever
b. On coilbox Z101, note the wire colors and
from S703.
carefully unsolder the wires connected from S703 to
e. In the AN/USM-159 only, in figures 6-1 and FO-
Z101 terminals 1 through 5 (fig. FO-6 or FO-7); then,
6, locate the 10K resistor (R308) connected
unsolder the wires on terminal 3 and the ground lug of
Z101. Mark or tag the wires.
6-21
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