TM 11-6625-3053-14
ITEM
MALFUNCTION
CHECKS/CORRECTIVE ACTION
16
Ext Pulse Modulation Not Functioning Properly.
1. Check for Pulse Modulation on A5 Assy.
a) Remove instrument dust cover (para 6-20).
b) Set up pulse generator as in Ext Pulse Electrical check step 9.
c) Connect pulse generator output cable to pulse jack
on front panel.
d) Set initial settings on sig gen.
e) Set up scope separately as in electrical check step 9 for probe
use.
f)
Energize system and wait 2 mins.
g) Set MODULATION Switch to EXT PULSE.
h) Using scope with probes, measure waveform between ground
and E2 on the A5 Leveling Attenuator Assy. Adjust scope
sensitivity as required.
Pulse should be displayed on scope.
If pulse not present, go to check 2 below.
If pulse displayed, check RF cable between E2 on A5 assy and
RF OUTPUT jack. If cable is good, replace A5 assy.
2. Check PULSE circuit in A3 card assy.
a) Continuing with scope, measure waveform on A3 card assy
between ground and collector of Q2 on the A3 card.
Pulse should be displayed on scope.
If pulse not displayed, go to check 3 below.
If pulse displayed, check wiring between collector of Q1 and E2
on A5 assy. Repair wiring if defective.
3. Q2 check.
a) Using multimeter, set to 100 VDC range. Measure voltage on the
collector of 02.
Voltage should be approx +11.8 VDC.
If voltage obtained, replace Q2.
If voltage not obtained, check power input to A3 card assy per
T/S item 12 check 1.e.
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