TM 55-4920-244-14
Table 4-1. Troubleshooting-Continued
Malfunction
Probable cause
Corrective action
8. Heater probes will not heat;
a. Defective voltage regulator.
a. Replace voltage regulator
20 amp fuse not blown.
b. Defective heater probe or
b. Replace heater probe or
heater cable.
heater cable.
a. Defective switch SW-2.
9. No temperature indication
with switch SW-2 in S-1
b. Defective wiring in ther-
b. Repair or replace wiring
position.
mocouple circuit.
c. Heater cable connector de-
c. Replace heater cable.
fective.
10. No temperature indication
a. Defective wiring in check
a. Repair or replace wiring
with switch SW-2 in S-2
cable thermocouple circuit,
position.
b. Defective switch SW-2.
11. Galvanometers (GALVO-1)
a. Defective switch SW-1.
a. Replace switch.
b. Open potentiometer (oC
cannot be set to zero with
potentiometer R-1.
scale).
4-42).
c. Defective potentiometer R-1.
d. Incorrect EGT indicator cir-
cuit reference voltage.
following components of
cable and printed circuit
board assembly, part no.
BH1766; T2, CR1, CR2,
CR3, CR4, CR5, CR6,
CR7, CR8, R2, R3, R13,
and R19. Replace defective
components (para. 4-17).
12. Galvanometers (GALVO-1)
a. Defective reference resistor.
cannot be set to zero by
following components:
adjusting resistance spool
R28, R29, R30, R31, R32,
in aircraft.
and R45. Replace defective
components (para. 4-17).
b. Replace printed circuit board
b. Defective printed circuit
assembly.
board assembly, part no.
BH1760.
c. Replace cable and printed
c. Defective cable and printed
circuit board assembly
circuit board assembly,
part no. BH1766.
d. Replace switch.
d. Defective switch SW-3.
a. Defective insulation check
13. INSULATION CHECK
meter,
meter will not zero with
b. Replace switch .
b. Defective switch SW-8.
insulation check adapter
c. Replace printed circuit board
c. Defective printed circuit
leads shorted and switch
assembly.
board assembly, part no.
SW-8 in either position.
BH1760.
d. Adjust circuit.
d. Circuit out of adjustment.
e. Defective adjustment po-
R40, R42, and R44. Replace
tentiometer.
defective components
4-9
Change 1
