Failure of the APU Ready Circuit

TASK 24-23-00-810-812-A
Failure of the APU Ready Circuit

1. Possible Causes

GAPCU [24XG]
GEN-APU [8XS]
C/B-APU GEN/EGIU2/115VAC [23XS]
wiring
RELAY-APU AVAIL [6KD]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
TSM TASK 24-00-00-810-803-A	Circuit Breaker Tripped and/or C/B TRIPPED Warning
ASM 242302
AMM 24-23-51-000-001	Removal of the APU Generator
AMM 24-23-51-400-001	Installation of the APU Generator
AMM 24-41-00-740-002	Operational Check of the GAPCU via the CFDS
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)
ASM 496101

3. Fault Confirmation
Subtask 24-23-00-740-058-A ** ON A/C NOT FOR ALL

A. Test
(1) Do the trouble shooting for all CFDS messages related to the Chapter 49 or to the ECB that can come into view with the CFDS message GEN APU (8XS)/ GAPCU (24XG)/ APU CTL RLY (6KD) (fault code 117, AGEN UF TRIP keyword).
(2) If no Chapter 49 or ECB-related CFDS messages come into view, or if the fault continues after the troubleshooting:

do a BITE test of the GAPCU AMM 24-41-00-740-002.

(a) If the BITE test gives the message TEST FAILED:

do the trouble shooting given in Para 4.A.

(b) If the BITE test gives the message TEST PASSED:

do the trouble shooting given in Para 4.B.

4. Fault Isolation
Subtask 24-23-00-810-072-A ** ON A/C NOT FOR ALL

A. If the BITE test gives the message TEST FAILED:

push the line key adjacent to the TEST FAILED message.

(1) If the maintenance message GAPCU (24XG) comes into view:

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

Subtask 24-23-00-810-069-A ** ON A/C NOT FOR ALL

B. If the BITE test gives the message TEST PASSED:

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

(1) If the fault continues:

Do a check of the status of the circuit breaker (23XS).

(a) If the circuit breaker is open:

Do the procedure (Ref. TSM TASK 24-00-00-810-803).

1 If the fault continues:

Replace the C/B-APU GEN/EGIU2/115VAC [23XS] .

(b) If the circuit breaker is closed:

Do a check of the wiring and the contact of the APU ready circuit ASM 496101 and ASM 242302 for a short to 28VDC between:
. pin B/6J of the ECB (59KD) and pin A/X1 of the APU AVAIL relay (6KD)
. pin A/7C of the GAPCU and pin A/A1 of the APU AVAIL relay
. pins A/A1 and A/A2 of the APU AVAIL relay (normally open).

Repair or replace the wiring as necessary
Replace the RELAY-APU AVAIL [6KD] as necessary.

(d) If the wiring or contact are correct:

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

Subtask 24-23-00-740-059-A ** ON A/C NOT FOR ALL

C. Do the test given in Para. 3.

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