TM 11-6625-847-45
Item
No.
Indication
Probable trouble
Procedure
a 600-cps square wave.
If square wave in not pres-
ent, check transistor Q1
for defects. Replace de-
fective parts.
d. If square wave Is present at
collector of transistor Q1,
connect the AN/USM-
140(*) probe to collector
of transistor Q2 and ob-
serve 500-cps square wave.
If square wave is not pres
ent, check transistor Q2,
capacitor A1C2 and resis-
tors A1R2 and A1R3 for
defects. Replace defective
parts.
8
The 1-usee pulse out-
a. Defective pulse shaping and
a. Perform the following:
put is not shown on
amplifier circuit (transistor
(1) Connect test equip-
the AN/USM-140(*)
Q6).
ment as described in
at connector J4; how-
ever, 150-usec and
(2) Connect the AN/USM-
85-usec pulse outputs
140(*) probe to
are observable at con-
collector of transis-
nectors J2 and J3.
tor Q8, and adjust
the AN/USM-140(*)
to observe a 500-
cps square wave. If
square wave is not
present, check tran-
sistor Q6, capacitor
C8, and resistors
A1R16 and A1R17
for defects. Replace
defective parts.
b. Defective differentiating and
b. If 500-cps square wave is
squaring circuit.
present at collector of tran-
sistor Q6, connect the
AN/USM-140(*) probe to
base of transistor Q7 and
adjust the AN/USM-
140(*) show 500-cps posi-
tive trigger pulse. If trig
ger pulses are not present,
check diodes A1CR4 and
A1CR5, resistor A1R18,
and capacitor A1C9 for
defect. Replace defective
parts.
c. Defective 8chmitt trigger
c. If positive trigger pulses are
multivibrator (transistors
present at base of transistor
Q8 and Q7).
Q7, connect the AN/USM-
140(*) probe to collector
of transistor Q8 and ad-
just the AN/USM-140(*)
to show 1-usec wide posi-
tive pulses (control R3
rotated fully clockwise).
2-12
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