Failure of the Exciter Field of the APU Generator

TASK 24-20-00-810-840-A
Failure of the Exciter Field of the APU Generator

1. Possible Causes

wiring
GEN-APU [8XS]
GCU-APU [1XS]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
ASM 242301
AMM 24-23-34-000-001	Removal of the GCU-APU
AMM 24-23-34-400-001	Installation of the GCU-APU
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 49-91-41-200-002	Remove and Discard Oil Filter Elements (131-9(A))

3. Fault Confirmation
Subtask 24-20-00-700-084-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 24-20-00-810-079-D ** ON A/C NOT FOR ALL

A. If the fault symptom is identified by the CFDS message CHECK GCU APU PIN C1 C5 GEN APU PIN A9 A10 and the upper ECAM DU warning APU GEN FAULT:

do a check of the wiring for an open circuit or a short to ground between:
. pin A/9 of the APU GEN (8XS) and pin AC/1 of the APU GCU (1XS)
. pin A/10 of the APU GEN and pin AC/5 of the APU GCU ASM 242301.

NOTE: Do the check of the oil filters AMM 49-91-41-200-002 for metal contamination.

(1) If the wiring is not correct:

repair it.

(2) If the wiring is correct:

do the check of the resistance of the exciter field of the APU GEN between pins A/9 and A/10 (7.67 Ohms plus or minus 0.73 Ohms at 25 deg.C) ASM 242301.

(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:

make sure there is electrical insulation between the pins A/9 and A/10 of the APU GEN and the case.

1 If there is no insulation:

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

2 If there is insulation:

replace the GCU-APU [1XS] AMM 24-23-34-000-001 and AMM 24-23-34-400-001.

NOTE: Do not remove the APU GCU before you do the other steps of the trouble shooting.

Subtask 24-20-00-700-085-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) De-energize the aircraft electrical circuits from the APU AMM 24-41-00-862-002.

[Rev.8 from Aug 2018] 2026.04.04 04:26:13 UTC