Failure of the APU AC Current Transformer or its Wiring

TASK 24-20-00-810-843-A
Failure of the APU AC Current Transformer or its Wiring

1. Possible Causes

wiring
CT-AC, APU GEN [42XS]
GEN-APU [8XS]
GCU-APU [1XS]

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 24-23-34-000-001	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

3. Fault Confirmation
Subtask 24-20-00-700-090-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 24-20-00-810-082-A ** ON A/C NOT FOR ALL

A. If the fault symptom is identified by the CFDS message CHECK CT 42XS GCU APU PIN B11A TO B11B WIRING and the upper ECAM DU warning APU GEN FAULT:

Do a check of the wiring for open circuit between respectively:
. the pins 1 to 4 of the APU generator AC current transformer and the APU GCU pins B/11A to B/11D
. the pins B/13A to B/13D of the APU GCU and the pins A/6, A/7, A/8, A/1 of the APU GEN ASM 242301.

(1) If the wiring is not correct:

repair it.

(2) If the wiring is correct:

Do an impedance check of the internal wiring of the AC current transformer between pins A/1 and successively pins A/2, A/3 and A/4 then do a check for open circuit between pins A/6 and successively A/1, A/2, A/3, A/4.

NOTE: The normal impedance between pin A/4 and each other pin is 10.15 Ohms plus or minus 3.45 Ohms at 25°C.

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

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

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

Do an impedance check of the internal wiring of the APU generator between pin A/1 and successively pins A/6, A/7 and A/8, then do a check for open circuit between pins A/1, A/6, A/7, A/8 and the case.

NOTE: The normal impedance between pin A/1 and each other pin is 24.1 Ohms plus or minus 2.41 Ohms at 25°C.

1 If the 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 values are in the specified limits:

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

Subtask 24-20-00-700-091-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