Failure of the APU generator AC Current Transformer or its Wiring

TASK 24-20-00-810-940-A
Failure of the APU generator AC Current Transformer or its Wiring

1. Possible Causes

CT-AC, APU GEN [42XS]
wiring
GAPCU [24XG]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
ASM 242301
AMM 24-23-17-000-001	Removal of the AC Current Transformer
AMM 24-23-17-400-001	Installation of the AC Current Transformer
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 24-20-00-869-094-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
Subtask 24-20-00-810-161-A ** ON A/C NOT FOR ALL

A. If the fault symptom is identified by the CFDS message CTA (42XS)/GAPCU (24XG) and the upper ECAM-DU warning APU GEN FAULT:

do an electrical resistance test of the APU generator AC current transformer (42XS) ASM 242301 between:
. pin 1 and pin 4 (10.15 ohms plus or minus 3.45 ohms)
. pin 2 and pin 4 (10.15 ohms plus or minus 3.45 ohms)
. pin 3 and pin 4 (10.15 ohms plus or minus 3.45 ohms).

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

replace the CT-AC, APU GEN [42XS] AMM 24-23-17-000-001 and AMM 24-23-17-400-001.

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

do a check of the wiring ASM 242301 for a short to ground, a short circuit, or an open circuit between:
. pin 1 of the APU generator AC current transformer and pin A/12B of the GAPCU
. pin 2 of the APU generator AC current transformer and pin A/12A of the GAPCU
. pin 3 of the APU generator AC current transformer and pin A/11A of the GAPCU
. pin 4 of the APU generator AC current transformer and pin A/11B of the GAPCU.

(a) If the wiring is not correct:

repair or replace as necessary.

(b) If the wiring is correct:

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

Subtask 24-20-00-860-164-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 04:26:25 UTC