TM 11-625-2575-14
filter FL501. The filter shall remain attached to
To replace the 1.0-, 10.0-, or 50.0-MHZ. plug-in
d. Remove two of the three 6-32 panhead screws
a. Remove the AN/USM-203A enclosure pan-
the backing panel.
e. Hold the oscillator with one hand, and care-
b. Remove the BNC connector which connects
fully remove the third screw. Except for two
to the adjacent plug-in marker, or, for the 1.0-
wires, the oscillator is detached.
MHz plug-in marker to Z602, the terminating
f. Position the oscillator so that the two wires
on the front panel may be unsoldered from feed-
through terminals C502 and C503.
c. Remove the screw which holds the marker
bracket to the chassis.
g. Remove the variable oscillator from the AN/
USM-203A.
d. Unplug the six-pin, plug-in marker from its
socket in the marker printed circuit board as-
h. Using the three screws removed in d and e
sembly.
above, attach the CENTER FREQUENCY dial
to the mating holes in the vernier drive.
e. Replace the defective marker with an opera-
i. Install an operating variable oscillator in the
tive marker of the same type.
AN/USM-203A by reversing the disassembly
f. Reverse the disassembly procedure.
procedure.
Section IV. TEST PROCEDURES
(2) ATTENUATOR - - - - -0dB.
1000 MHz.
(3) CENTER FRE-
When an AN/USM-203A has been repaired, per-
QUENCY.
(4) SWEEP RATE - - - -MANUAL.
10, 7-11, 8-15, and 8-16.
NARROW.
(5) SWEEP WIDTH
switch.
NOTE
Fully counterclockwise.
(6) SWEEP WIDTH
vernier.
Results of the test procedures may indi-
(7) ALC - - - - - - - - - - - - - -INT.
cate that further troubleshooting, re-
(8) MARKERS - - - - - - - -All OFF.
pair, and alignment must be performed.
Section VI provides additional align-
c. Energize both the unit under test and the
ment and adjustment procedures that
counter.
should enable the unit under test to
d. Set the SWEEP RATE vernier fully clock-
meet the technical
characteristics
wise, and read the counter frequency.
e. Set the SWEEP RATE vernier fully counter-
If the unit cannot be made ready for use, it shall
clockwise, and read the counter frequency.
be sent to the depot for evaluation.
f. Subtract the
frequency obtained in
e above
from the frequency obtained in d above.
g. The frequency difference shall be 10 kHz
maximum.
8-15. Minimum Sweep Width
h. Set the unit under test controls as in b
a. Connect the RF OUT connector of the unit
above, but set the SWEEP WIDTH switch to
under test to the input of Electronic Counter,
WIDE.
Digital Readout AN/USM-207A. Use a 50-ohm
BNC-to-BNC cable approximately 30 inches long.
i. Set the SWEEP RATE vernier fully clock-
wise, and read the counter frequency.
b. Set the front panel controls of the unit under
test as follows:
j. Set the SWEEP RATE vernier fully counter-
(1) BAND - - - - - - - - - - - - - - - - - - HIGH.