TM 11-6625-847-45
Item
No.
Indication
Probable trouble
Procedure
output coupling capacitors
A1C6 and A1C7 for defects.
Replace defective parts.
2-20. Troubleshooting Chart, Test Set (IF Oscillators A1A2, A1A3, and A1A4)
Item
No.
Indication
Probable trouble
Procedure
1
The AN/USM-140(*)
Defective potentiometer control
With no power or signal inputs
output level indication
R1.
connected to the oscillator
or the AN/URM-
assembly, connect the AN/
145 does not vary when
PSM-6B between. terminal 5
potentiometer con-
and ground. Rotate the po-
trol R1 in varied from
tentiometer from fully coun-
fully counterclock-
terclockwise to fully clock-
wise to fully clock-
wise, and check the AN/PSM-
wise.
6B for a resistance variation
from 0 to 250 ohms. Replace
potentiometer R1 if defec-
tive
2
Electronic Counter,
Defective crystal Y1 or capaci-
Replace crystal Y1 or capacitors
Digital Readout. AN/
tors C1 and C2 in A1.
C1 and C2 in A1, if defective.
USM-207 does not
indicate the correct
frequency for the oscil-
lator under test.
3
Frequency indication on
Defective variable capacitor A1C1.
Replace variable capacitor A1C1.
the AN/USM-207
does not vary when
variable capacitor C1
is rotated through its
full travel.
4
Oscillator output level
a. Defective crystal tank cir-
a. Perform the following:
from A1 is not indi-
cuit.
(1) Connect test equip-
ted on the AN/URM-
ment as described
145 with potentiometer
R1 adjusted fully
(2) Adjust the AN/USM-
clockwise.
140(*) to show a
1.75mc signal.
(3) Connect the AN/USM-
140(*) probe to
base of transistor
Q1 (turn gain con-
trol up on the AN/
USM-140(*) and
check for a 1.75-mc
sinusoidal signal.
if signal is not pres-
ent, cheek crystal
Y1 and on A1 (fig.
and CR2, resistors
R2, R4, and RT1,
and capacitors C1
2-14
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