Message Name:

APU GEN [DIFF PROTECTION FEEDER]

Message Code:

2420124LPS

Associated CAS:

APU GEN FAIL
(Advisory)

Auxiliary Power Unit (APU) Generator has tripped off-line or will not come on-line.

• Auxiliary Power Unit (APU) Generator Control Unit (GCU) (A109)
• Auxiliary Power Unit (APU) Generator (A110)
• AC Power Center (ACPC) (A54)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Flight Operation Notifications Manual (FONM): None

NOTES:

• A GCU patch cable (GSE REF # 24X-24-02) can be used to interchange GCUs 1, 4 and 5 into position 2 or 3 (for troubleshooting only).

• The GCU NVMs can only be downloaded at position #2 or #3.

1. Access CAIMS active faults. Are there any ACPC related fault messages?

   1. If YES, troubleshoot these messages first.
   2. If NO, continue with next step.

2. Interchange APU GCU with GCU #2 (physically or using the GCU patch cable).
   NOTE: Use PMAT to monitor the fault on GCU.

   1. If system checks are good, replace APU GCU and do close out.
   2. If fault remains, continue with next step.

3. Disconnect APU GCU connector (A109P2) and APU Generator connector (A110P1). Do a continuity check as follows:

   From	To	Result
   A109P2-41	Ground
   A109P2-42	Ground
   A109P2-50	Ground
   A109P2-40	Ground

   1. If there is continuity, repair defective wiring as required.
   2. If there is no continuity, continue with next step.

4. Do a continuity check as follows:

   From	To	Result
   A109P2-41	A110P1-F
   A109P2-42	A110P1-E
   A109P2-50	A110P1-J
   A109P2-40	A110P1-D

   1. If there is continuity, continue with next step.
   2. If there is no continuity, repair defective wiring as required.

5. Disconnect ACPC connector (A54P4). Do a continuity check as follows:

   From	To	Result
   A109P2-49	Ground
   A109P2-57	Ground
   A109P2-63	Ground
   A109P2-62	Ground

   1. If there is continuity, repair defective wiring as required.
   2. If there is no continuity, continue with next step.

6. Do a continuity check as follows:

   From	To	Result
   A109P2-49	A54P4-E
   A109P2-57	A54P4-F
   A109P2-63	A54P4-G
   A109P2-62	A54P4-H

   1. If there is continuity, continue with next step.
   2. If there is no continuity, repair defective wiring as required

7. Disconnect APU Generator (A110) (T1, T2 and T3) and ACPC APU GEN -A, B and C.
8. Do an Insulation check using a megger as follows:
   Caution: Before using the megger, make sure both sides of cable are disconnected. Failure to do that may damage the equipment

   From	To	Expected Result	Result
   A110-T1	Ground	No Continuity
   A110-T2	Ground	No Continuity
   A110-T3	Ground	No Continuity

   1. If there is continuity repair defective wiring and do close out.
   2. If there is no continuity, continue with next step.

9. Do an Insulation check using a megger as follows:
   Caution: Before using the megger, make sure both sides of cable are disconnected. Failure to do that may damage the equipment

   From	To	Expected Result	Result
   A110-T1	A110-T2	No Continuity
   A110-T1	A110-T3	No Continuity
   A110-T1	A110-G	No Continuity
   A110-T2	A110-T3	No Continuity
   A110-T2	A110-G	No Continuity
   A110-T3	A110-G	No Continuity

   1. If there is continuity repair defective wiring and do close out.
   2. If there is no continuity, continue with next step.

10. Do a continuity check as follow:

    From	To	Expected Result	Result
    A110-T1	ACPC APU GEN-A	Continuity
    A110-T2	ACPC APU GEN-B	Continuity
    A110-T3	ACPC APU GEN-C	Continuity
    A110-G	Ground	Continuity

    1. If there is continuity, continue with next step.
    2. If there is no continuity, repair defective wiring as required

11. Replace the APU Generator. Is the fault still present?

    1. If YES, continue with next step.
    2. If NO, do close out.

12. Replace ACPC.
13. Do close out.