TM 11-5840-281-35/1
Item No.
Trouble symptom
Probable trouble
Checks and corrective action
(SCAN MODE switch on master
positioned at -15 degrees cw from
Control-Indicator C-6988/TPN-18
0 degree as indicated on azimuth
placed to NORM, 850 EL, or 600
protractor. Angle data voltage
AZ).
should be -8.7v. If angle data
voltage is abnormal perform below.
If angle data voltage is normal, see
item 13 above.
b. Perform azimuth angle data
potentiometer and electronic filter
adjustments (para 3-24). If
condition is not corrected by
adjustments, check angle data
voltage at ANGLE DATA testpoint
TP702 on elevation electronic filter
with elevation Antenna AS-
1291/TPN-8positioned at dead
bottom of its scan. Angle data
voltage should be -1.5v. If angle
data voltage is normal, see item 13
above. If angle data voltage is
abnormal, performance below.
c. Check -85v supply voltage a-85v
testpoint TP3402 on 85v voltage
regulator in Radar Receiver-
Transmitter RT-818/TPN-18. If
abnormal; adjust-35v ADJ R3427
for indication of -35v at -35v
testpoint TP8402. If condition is not
corrected by adjustment, replace
35v voltage regulator.
a. If crystal current is low in one or two
16 Abnormal mixer crystal currents
LO ATTEN AT104 (local oscillator)
of four positions of XTAL CUR
indicated on XTAL CUR meter
attenuator misadjusted or
switch S104 (SUM1,SUM2,DIFF1,
M101 on Radar Receiver-
defective, local oscillator V103
and DIFF2), substitute respective
Transmitter RT-818/ TPN-18
misadjusted or defective, or
crystal diode (CR121 thru CR124).
control panel.
defective mixer crystal diodes
b. If crystal current indications on
(CR121 thru CR124).
XTAL CUR meter M101 is low in all
positions of XTAL CUR switch
S104, perform local oscillator
alignment (para 8-81).
a. Local oscillator mistuned ..............
a. Perform local oscillator alignment
17 Low receiver noise (less than
0.2vpeak at DET VIDEO testpoint
channel alignment (para 3-32).
TP301 on Intermediate Frequency
b. Low receiver minimum discernible
b. Perform sum receiver channel test
Amplifier AM-3339/TPN-8.
signal (mds).
(para 44).
c. Defective sum channel mixer
c. Replace sum channel signal mixer
crystals.
crystal diodes CR121 and CR122.
If condition still exists, check tubes
in sum channel Intermediate
Frequency Amplifier AM9337/TPN-
8. If condition still exists, replace
Intermediate Frequency Amplifier
AM-439/TPN-8.
a. Defective ftc control circuit.
a. If Control-Indicators C-6988/ TPN-
18 No ftc response on displays when
18 are installed in Landing Control
FTC switch on master Control-
Central AN/TSQ-71A, elect other
Indicator C-6988/TPN-18 is placed
Control-Indicator C-6988/ TPN-18
to ON.
as master by placing
3-6
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