TM 11-5840-281-5/I1
Item No.
Trouble symptom
Probable trouble
Checks and corrective action
b. Defective sensitivity time control
b. Replace sensitivity time control
circuit card.
circuit card.
c. Defective Remote Switching
c. Replace Remote Switching Control
Control C-6989/TPN-18.
C-6989/TPN-18
23 Receiver noise is not gated-off
GATE WIDTH control on sensitivity
Perform sensitivity time control
approximately 700sec after
time control circuit card
alignment (para 3-35). If condition
pretrigger time as observed on
misadjusted.
still exists, replace sensitivity time
oscilloscope at DET VIDEO
control circuit card.
testpoint TP301 on Intermediate
Frequency Amplifier AM-3339/TPN-
8.
Sensitivity time control.........................
Same as item 23 above.
24 Abnormal waveforms at SUM
GAIN testpoint TP3902 or DIFF
GAIN testpoint TP3908.
a. High or unstable primary power
a. Check primary power input for
25 Radar transmitter high voltage will
input.
stable 120/208 vac.
not stay on.
b. High voltage overload circuit
b. Excessive magnetron current due
removes high voltage due to
to high prf. Check indication on
overload.
MAG CUR meter M201 for less
than 26 main wide pulse or less
than 7 main narrow pulse. If
excessive, perform radar
transmitter alignment ( para 3-30).
Inspect all waveguides in radar set
group for bent or damaged
sections and loose connections.
c. Arcing .........................................
c. If power has not been applied to
radar transmitter for an extended
period of time or magnetron is
new, operate 15 minutes with high
voltage off, then operate 2 hours
minimum in 1/2-power mode
NORMAL-1/2 POWER switch
S202 on radar transmitter placed
to 1/2-POWER and
TRANSMITTER switch on master
Control-Indicator C-6988/TPN-18
placed thru WIDE to HV ON).
d. Defective magnetron
d. Replace magnetron.
26 Radar transmitter high voltage will
a. Defective TRANSMITTER switch
a. If two Control-Indicators C-
not come on when
circuit in Control-Indicator C
6988/TPN-18 are installed in
TRANSMITTER switch on master
6988/TPN-18.
Landing Control Central AN/TSQ-
Control-Indicator C-4988/TPN-18
71A, select other Control-Indicator
is placed thru WIDE or NARROW
C-6988/TPN-18 as master by
to HV ON.
placing MASTER IND selector
switch on Indicator Control C-
7012/TPX to alternate position (1 or
2, as applicable). If condition is
corrected, trouble is in
TRANSMITTER switch circuit of
Control- Indicator C-6988/TPN-18.
b. Defective high voltage circuit in
b. Replace radar transmitter or refer to
radar transmitter.
higher category maintenance.
27 Low rf power output measured at
a. Low prf....................................................
a. Measure interpulse period at PRE
azimuth directional coupler.
TRIG testpoint TP211 with
oscilloscope. If interpulse period is
not 833+40 sec, adjust PRF ADJ
control R247 on radar transmitter
for 833 sec (pars 3-30).
b.
b. Replace magnetron.
Defective magnetron
3-8
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