TM 1-1520-238-T-4
4–99
4–20.
ENG START CIRCUIT BREAKER – DOES NOT STAY CLOSED (WITH ENG START NO 1
4–20
SWITCH IN START POSITION)
Tools:
Nomenclature
Part Number
Tool Kit, Electrical
SC518099CLA06
Repairer’s
Multimeter, Digital
AN/PSM-45
Personnel Required:
68F
Aircraft Electrician
One person to assist
References:
TM 1-1520-238-T-6
TM 1-1520-238-23
WARNING
Turn off power before detaching or
attaching wires and connectors. High
current 28 VDC or 115 VAC is present.
Failure to do so could result in death or
serious injury.
1. Open ENG START circuit breaker. Check for
short between (A76):
J1–c and ground,
J1–X and ground.
Does short exist?
YES
Refer to TM 1-1520-238-T-6 to
troubleshoot circuit protection
system (dc emergency bus –
pilot station).
NO
Go to step 2.
2. Set and hold ENG START NO 1 switch in
START position. Check for short between
P463–X and ground.
Does short exist?
YES
Go to step 3.
NO
Go to step 4.
3. Detach P173. Check for short between P463–X
and ground.
Does short exist?
YES
Repair shorted wire between
P463–X and P173–V.
Go to paragraph 4–12.
NO
Go to step 5.
4. Detach P439. Check for short between P463–c
and ground.
Does short exist?
YES
Repair shorted wire between
P463–c and P439–A14.
Go to paragraph 4–12.
NO
Go to step 8.
5. Check for short between P173–L and ground.
Does short exist?
YES
Go to step 6.
NO
Replace pilot power quadrant
(TM 1-1520-238-23).
6. Check for short between between P977–B3 and
ground.
Does short exist?
YES
Go to step 11.
NO
Go to step 7.
7. Detach P463. Check for short between
P977–A14 and ground.
Does short exist?
YES
Repair shorted wire between
P173–L and P977–A14.
Go to paragraph 4–12.
NO
Replace start mode relay panel
(TM 1-1520-238-23).
8. Check for short between P439–A2 and ground.
Does short exist?
YES
Go to step 9.
NO
Go to step 12.
