Failure of the Fault Light Circuit of the APU Generator

TASK 24-41-00-810-815-A
Failure of the Fault Light Circuit of the APU Generator

1. Possible Causes

wiring
GAPCU [24XG]
BOARD-ANN LT TEST & INTFC [10LP]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
ASM 242202
ASM 242302
AMM 24-41-00-740-002	Operational Check of the GAPCU via the CFDS
AMM 24-41-34-000-001	Removal of the Ground Power Control Unit (GPCU)
AMM 24-41-34-400-001	Installation of the Ground Power Control Unit (GPCU)
AMM 33-14-33-000-001	Removal of the Annunciator-Light Test and Interface-Board
AMM 33-14-33-400-001	Installation of the Annunciator-Light Test and Interface-Board

3. Fault Confirmation
Subtask 24-41-00-740-063-A ** ON A/C NOT FOR ALL

A. Test
(1) Read the Class 3 Faults of the GAPCU AMM 24-41-00-740-002.

4. Fault Isolation
Subtask 24-41-00-810-086-A ** ON A/C NOT FOR ALL

A. If the Class 3 Faults gives the maintenance message GAPCU (24XG)/ANN LT BOARD (10LP):

do a check of the wiring ASM 242302 ASM 242202 for a short to ground between:
. pin A/5G of the GAPCU and pin A/28 of the annunciator light test and interface board (10LP)
. pin A/29 of the annunciator light test and interface board (10LP) and pin 11 of the diode module 2422VD
. pin 26 of the diode module 2422VD and pin 18 of the GLC APU (3XS)
. pin 20 of the GLC APU and pin 26 of the EPC (3XG)
. pin 28 of the EPC and pin A/A1 of the APU AVAIL relay (6KD)
. pin A/A2 of the APU AVAIL relay and pin 37 of the diode module 1162VD.

(1) If there is a short to ground:

repair or replace the wiring as necessary.

(2) If there is no short to ground:

replace the GAPCU [24XG] AMM 24-41-34-000-001 and AMM 24-41-34-400-001.

(3) If the fault continues:

replace the BOARD-ANN LT TEST & INTFC [10LP] AMM 33-14-33-000-001 and AMM 33-14-33-400-001.

Subtask 24-41-00-810-086-C ** ON A/C NOT FOR ALL

A. If the Class 3 Faults gives the maintenance message GAPCU (24XG)/ANN LT BOARD (10LP):
(1) Do a check of the wiring , ASM 242302, ASM 242202, for a short to ground between:

Pin A/5G of the GAPCU (24XG) and pin A/28 of the annunciator light test and interface board (10LP)
Pin A/29 of the annunciator light test and interface board (10LP) and pin 11 of the diode module 2422VD
Pin 26 of the diode module 2422VD and pin 18 of the GLC APU (3XS)
Pin 20 of the GLC APU (3XS) and pin 26 of the EPC (3XG)
Pin 28 of the EPC (3XG) and pin A/A1 of the APU AVAIL relay (6KD)
Pin A/A2 of the APU AVAIL relay (6KD) and pin A/A2 of the APU-GLC auxiliary control-relay (4XS)
Pin A/A3 of the APU-GLC auxiliary control-relay (4XS) and pin 2 of circuit breaker 5XU.

(a) If there is a short to ground:

Repair the wiring.

(b) If there is no short to ground:

Replace the GAPCU [24XG] AMM 24-41-34-000-001 and AMM 24-41-34-400-001.

Replace the BOARD-ANN LT TEST & INTFC [10LP] AMM 33-14-33-000-001 and AMM 33-14-33-400-001.

Subtask 24-41-00-740-064-A ** ON A/C NOT FOR ALL

B. When you replace a component or repair the wiring:

do the subsequent flight before you do the check of the Class 3 Faults of the GAPCU from the CFDS to make sure that the system operates correctly.
If the test continues to give the fault message, continue the trouble shooting procedure.

[Rev.8 from Aug 2018] 2026.04.04 04:26:54 UTC