Message Name:

GCU1 [VOLTAGE REGULATOR LOW]

Message Code:

2421107LPS

Associated CAS:

GEN 1 FAIL
(Advisory)

Generator Control Unit (GCU) #1 has detected a voltage regulator low failure, consequently resulting in a Generator #1 to tripped off-line or not come on-line.

• Generator Control Unit (GCU) 1 (A56)
• Variable Frequency Generator (VFG) 1 (G1)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Flight Operation Notifications Manual (FONM): None

NOTES:

• The GCU NVMs can only be downloaded at position #2 or #3.
• A GCU patch cable (GSE REF # 24X-24-02) can be used to swap GCU 1, GCU4 and APU GCU into position 2 or 3 (for troubleshooting only)

1. Remove power from the A/C completely. Apply power back on the A/C. Is the fault still present?

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

2. Interchange GCU 1 with GCU 2. Is the fault still present?

   1. If YES, continue with next step.
   2. If NO, replace defective GCU.

3. Disconnect VFG 1 connector G1P1, ACPC connector A54P6 and GCU 1 connector A56P1. Do a continuity check as follows:

   From	To	Result
   A56P1-J	Ground
   A56P1-K	Ground
   A56P1-A	Ground
   A56P1-B	Ground
   A56P1-C	Ground

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

4. Do a continuity check as follows:

   From	To	Result
   A56P1-J	G1P1-H
   A56P1-K	G1P1-B
   A56P1-A	A54P6-A
   A56P1-B	A54P6-B
   A56P1-C	A54P6-C

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

5. At VFG, disconnect G terminal.
6. Perform a continuity check on aircraft wiring side as follow:

   From	To	Result
   G1-G	Ground

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

7. Replace VFG 1.
8. Do close out.