TM 55-4920-401-13&P
Table 4-8. Heater Probe Control Circuit Troubleshooting Table.
Heater probes will not heat.
Heater probes heat too slowly.
H e a t e r p r o b e t e m p e r a t u r e c a n-
not be set with PROBE CONTROL.
H e a t e r p r o b e t e m p e r a t u r e e x-
c e s s i v e l y o v e r s h o o t s o r u n d e r-
shoots temperature setting.
Heater probes heat continuously.
H e a t e r p r o b e t e m p e r a t u r e a nd
set temperature differ more than
+ 4ºC.
a. Defective heater cable
b. Probe controller circuit
breaker CB1 open
c. Relay K1 defective
d . P r o b e c o n t r o l l e r
transformer T1 defective
e. Defective amplifier (A 1
or A2) transformer (T1), or
silicon controlled rectifier
(SCR2) on probe control and
function switch board.
f. Voltage at test point 43
n o t i n
p h a s e
w i t h
line voltage
g . S C R 2 ( r e c t i f i e r
furthest from transformer
T1 inside probe control
compartment defective.
a. SCR1 on probe control
and function switch board
defective
b. SCR1 rectifier nearest
transformer T1 inside probe
c o n t r o l c o m p a r t m e n t )
defective
a . P R O B E C O N T R OL
defective
b . T E M P E R A T U R E
switch defective
a. Q3 on probe control and
f u n c t i o n s w i t c h b o a r d
defective
a. A1, A2, Q2, SCR1, or
SCR2 on probe control and
f u n c t i o n s w i t c h b o a r d
defective
b. SCR1 or SCR2 (recti-
fiers inside probe control
compartment defective
a. Fewer than 8 heater
p r o b e s b e i n g u s e d w i th
tester.
b. Heater probe control
circuit out of calibration.
a. Repair or replace cable.
b. Replace circuit breaker
(30, figure FO-8)
c. Replace relay (28).
d. Replace transformer (2).
e. Check waveforms per para.
4-7e and replace defective
component.
f. Check phasing and correct at
transformer T1 on probe control
and function switch board.
g. Replace rectifier.
a. Replace rectifier
(11, figure 4-37).
b. Replace rectifier.
a. Replace control (20, figure
FO-8)
b. Replace switch (23, figure
4-31).
a. Check waveform per
para. 4-7e and replace Q3
(49, figure 4-37) if defective.
a. Check waveforms
per para. 4-7e and replace
defective component.
b. Replace detective
rectifier.
a. Calibrate heater probe
control circuit.
b. Calibrate circuit.
4-10
