Fault Message:

ACPC PRIMARY LOGIC #3-A21/RS422

Fault Code:

2483900ACP

Associated CAS:

None

AC Power Center (ACPC) Primary Logic Card (PLC) 3 has detected a problem on the RS422 communication bus between itself and Generator Control Unit (GCU) 1.

• Generator Control Unit (GCU) 1 (A56)
• AC Power Center Primary Logic Card (PLC) 3
• AC Power Center (ACPC) (A54)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

NOTE: If this CAIMS message is observed at a time when the aircraft had been in the ground service mode, the message can be considered as nuisance.

• The messages is caused by a loss of communication between the Generator Control Units (GCU) and ACPC card. This loss of communication occurs as a normal function of the electrical system once the aircraft is in ground service mode. The battery bus is shed, which removes power from the GCU, resulting in loss of communication between the GCUs and ACPC cards
• Take note that there will be no indication in the cockpit as it is “black” when in ground service mode

1. Swap GCU 1 with GCU 2, 3, 4 or APU GCU. Is the fault resolved?

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

2. Access ACPC logic assembly. Swap PLC 3 with PLC 1. Is the fault still present?

   1. If NO, replace PLC 3 and do close out.
   2. If YES, continue with next step.

3. Disconnect GCU 1 connector A56P2 and remove PLC 3. Perform a continuity check as follows:

   From	To	Result
   A56P2-9	Ground
   A56P2-15	Ground

   1. If there is continuity, go to step 5.
   2. If there is no continuity, continue with next step.

4. Perform a continuity check as follows:

   From	To	Result
   A56P2-9	P415B-44
   A56P2-15	P415B-45

   1. If there is continuity, replace PLC 3 and do close out.
   2. If there is no continuity, go to step 6.

5. Disconnect ACPC connector A54P6. Perform a continuity check as follows:

   From	To	Result
   A54P6-a	Ground
   A54P6-b	Ground

   1. If there is continuity, repair defective wiring as required and do close out.
   2. If there is no continuity, go to step 7.

6. Disconnect ACPC connector A54P6. Perform a continuity check as follows:

   From	To	Result
   A56P2-9	A54P6-a
   A56P2-15	A54P6-b

   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 ACPC.
8. Do close out.