TM 11-5840-281-35/1
Item No.
Trouble symptom
Probable trouble
Checks and corrective action
Receiver-Transmitter RT-818/TPN-
18. Precision relay K101 should be
restored; iff interlock relay K102
should be operated.
c. Check for presence of error signal
from transformer B40101 (in
associated iff equipment) at AZ
POS FB testpoint TP7501 on
electronic control preamplifier.
2 Ppi sweep on either Control-
Refer to applicable associated iff
Defective synchro transmitter B40102
Indicator C-6988/TPN-18 not
equipment technical manual.
in associated iff equipment.
synchronized with associated iff
antenna when respective SCAN
MODE switch is placed to IFF.
Replace iff mode relay K602 in
3 Ppi sweep on one Control-Indicator
Defective iff mode relay K602 in
applicable Control-Indicator C-
C-6988/TPN-18 not synchronized
applicable Control-Indicator C-
6988/TPN-18.
with associated iff antenna when
6988/TPN-18.
operating in IFF scan mode.
Perform precision scan mode
4 Indicated bearing of radar targets on
Synchro control system misaligned ...
alignment (para 3-27). If operated
both Control-Indicators C-
with associated iff equipment, also
6988/TPN-18 incorrect in SEARCH
perform iff antenna orientation
and SIMULT scan modes.
alignment (TM 11-5840-281-12).
Replace trigger delay generator or
5 No range marks ............................
Defective trigger delay generator
range mark oscillator circuit card.
circuit card or range mark oscillator
circuit card in applicable Pulse
Generator O-1333/TPN-18.
6 No touchdown markers .................
Replace range mark oscillator circuit
Defective range mark oscillator circuit
card.
card in applicable Pulse Generator
0-1833/TPN-18.
7 No range mark blanking ................
Replace azimuth-elevation blanking
Defective azimuth-elevation blanking
pulse generator or range mark
pulse generator or range mark
generator circuit card.
generator circuit card in applicable
Pulse Generator 0-1383/TPN-18.
a. In either Control-Indicator C-
8 No sweeps on both Control-
No system trigger ..............................
6988/TPN-18, place TRIG switch
Indicators C-6988/TPN-18 in any
S2201 on trigger delay generator
scan mode.
circuit card to INT. If sweep
appears, return TRIGGER switch
S2201 to EXT and perform b or c
below.
b. If operated with an associated iff
equipment, check associated iff
equipment triggers.
c. If operated independent of an
associated if equipment, trouble is
probably in trigger generator circuit
of radar transmitter.
a. Adjust SWEEP GATE LENGTH
9 Sweep ends before 40-mi range
Misadjustment of SWEEP GATE
control R4503 to end sweep just
mark on ppi sweep with SCAN
LENGTH control R4503 on sweep
after 40-mi range mark on ppi
MODEswitch placed to SEARCH
generator circuit card or defective
sweep with SCAN MODE switch on
and RANGE MILES switch placed
sweep generator circuit card.
Control-Indicator C-6988/TPN-18
to 40.
placed to SEARCH and RANGE
MILES switch placed to 40.
b. If adjustment does not correct
trouble, replace sweep generator
circuit card
3-11
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