Failure of the APU Generator PMG-Stator or the Exciter Field or its Wiring to the GAPCU

TASK 24-23-00-810-811-A
Failure of the APU Generator PMG-Stator or the Exciter Field or its Wiring to the GAPCU

1. Possible Causes

GEN-APU [8XS]
wiring
GAPCU [24XG]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
ASM 242301
AMM 24-23-51-000-001	Removal of the APU Generator
AMM 24-23-51-400-001	Installation of the APU Generator
AMM 24-41-00-861-002	Energize the Aircraft Electrical Circuits from the External Power
AMM 24-41-00-862-002	De-energize the Aircraft Electrical Circuits Supplied from the External Power
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)

3. Fault Confirmation
Subtask 24-23-00-869-058-A ** ON A/C NOT FOR ALL

A. Test
Not applicable.

NOTE: As the APU GEN was set to OFF because of a true failure, the fault confirmation is not necessary.

4. Fault Isolation

CAUTION: BEFORE YOU START THE CHECK OF IDG WIRING THAT INCLUDES CONNECTORS, EXAMINE EACH CONNECTOR TO MAKE SURE THAT THERE IS NO CONTAMINATION IN IT. IF YOU FIND CONTAMINATION, CLEAN THE CONNECTOR AND CONNECT IT AGAIN. IF THE FAILURE CONTINUES, DO THE TROUBLE SHOOTING PROCEDURE AS GIVEN BELOW.

Subtask 24-23-00-810-067-B ** ON A/C NOT FOR ALL

A. If the fault symptom is identified by the CFDS message GAPCU (24XG)/GEN APU (8XS) PMG and the upper ECAM-DU warning APU GEN FAULT:

do a check of the resistance of the APU generator exciter-field between pins A/9 and A/10 of the APU generator (7.67 ohms plus or minus 0.73 ohms) ASM 242301.

(1) If the resistance values are out of the specified limits:

replace the GEN-APU [8XS] AMM 24-23-51-000-001 and AMM 24-23-51-400-001.

(2) If the resistance values are in the specified limits:

do a check of the resistance of the APU generator PMG-stator ASM 242301 between:
. pins A/12 and A/13 of the APU generator (0.868 ohm plus or minus 0.156 ohm)
. pins A/12 and A/14 of the APU generator (0.868 ohm plus or minus 0.156 ohm)
. pins A/13 and A/14 of the APU generator (0.868 ohm plus or minus 0.156 ohm).

(a) If the resistance values are out of the specified limits:

replace the GEN-APU [8XS] AMM 24-23-51-000-001 and AMM 24-23-51-400-001.

(b) If the resistance values are in the specified limits:

do a check of the wiring for a short to ground, a short circuit or an open circuit between:
. pin A/12 of the APU generator and pin C/10 of the GAPCU
. pin A/13 of the APU generator and pin C/11 of the GAPCU
. pin A/14 of the APU generator and pin C/9 of the GAPCU
. pin C/7 and pins C/10, C/11 and C/9 of the GAPCU
. pin A/9 of the APU generator and pin C/12 of the GAPCU
. pin A/10 of the APU generator and pin C/13 of the GAPCU
. pin C/7 and pins C/12, C/13 of the GAPCU.

1 If the wiring is not correct:

repair or replace as necessary.

2 If the wiring is correct:

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

Subtask 24-23-00-860-060-A ** ON A/C NOT FOR ALL

B. Make sure that the aircraft electrical circuits operate correctly in APU configuration.
(1) Energize the aircraft electrical circuits from the APU AMM 24-41-00-861-002.
(2) Let the APU generator operate for five minutes to make sure that it operates correctly.
(3) De-energize the aircraft electrical circuits from the APU AMM 24-41-00-862-002.

[Rev.8 from Aug 2018] 2026.04.04 04:26:39 UTC