Failure of the ARINC 429 Bus betwwen the GAPCU and the CFDIU

TASK 24-41-00-810-825-A
Failure of the ARINC 429 Bus betwwen the GAPCU and the CFDIU

1. Possible Causes

wiring
GAPCU [24XG]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 24-41-00-740-002	Operational Check of the GAPCU via the CFDS
ASM 244101
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 24-41-00-740-065-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 24-41-00-810-087-B ** ON A/C NOT FOR ALL

A. If the Class 3 Faults gives the maintenance message CFDIU(1TW)/GAPCU (24XG):
(1) Do the trouble shooting for chapter 31 or CFDIU messages that come into view with this message.
(2) If there are no chapter 31 or CFDIU messages or if the fault continues after the trouble shooting :

do a check of the wiring of the ARINC 429 bus ASM 244101 for an open circuit, a short circuit, a short to ground or a short to shield between:
. pin A/7E of the GAPCU and pin B/11E of the CFDIU (1TW)
. pin A/8E of the GAPCU and pin B/11D of the CFDIU
. pins A/7E and A/9E of the GAPCU
. pins A/8E and A/9E 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 24-41-00-740-066-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