Message Name:

APUGCU H/W OVERVOLTAGE SENSE FAULT

Message Code:

2420175LPS

Associated CAS:

APU GEN FAIL
(Advisory)

The Auxiliary Power Unit Generator Control Unit (APU GCU) has detected a hardware over-voltage failure on initial power-up, consequently preventing the Generator to come on-line.

• Auxiliary Power Unit (APU) Generator Control Unit (GCU) (A109)
• Auxiliary Power Unit (APU) Generator (A110)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Notice To Operators (NTO): None

Flight Operation Notifications Manual (FONM): None

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).

1. With connectors A109P1 (APUGCU) and A110P1 (APU GEN) disconnected, perform a wiring check as follows:
   

   From	To	Expected Result	Result
   A110P1-H	A109P1-J	Continuity
   A110P1-B	A109P1-K	Continuity
   A110P1-B	GND	Open
   A110P1-H	GND	Open

   1. If a short to ground fault is detected, repair or replace defective associated wiring and do close out.
   2. If no short to ground fault is detected, continue with next step.
      NOTE: A megohm meter may be required to detect fault.

2. Interchange APU GCU with GCU 3 (or use the patch cable).

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

3. Replace APU Generator.
4. Do close out.