Fault Message:

EMS CDU 1/ACPC LEFT FTM-A20/WRG

Fault Code:

2470103CDU

Associated CAS:

ELEC SYS FAULT
(Advisory)

ARINC 429 communication between the AC Power Center (ACPC) and the Electrical Management System Control and Display Unit (EMS CDU) is faulty. The LRU transmits on periodic basis a test label that is turned around by the receiving LRU.

• Electrical Management System Control and Display Unit (EMS CDU) 1 (A94)
• AC Power Center (ACPC) (A54)
• AC Power Center (ACPC) Microprocessor Card
• Junction Box (JB3)/PCB3
• Junction Box (JB3)
• Primary Logic Card (PLC) 1
• Primary Logic Card (PLC) 2
• Primary Logic Card (PLC) 3
• Secondary Logic Card (SLC) 1
• Secondary Logic Card (SLC) 2
• Secondary Logic Card (SLC) 3
• Secondary Logic Card (SLC) 4
• Solid-State Power Controller (SSPC)
• AC-to-DC Converter Card
• AC Power Center (ACPC) External Power Quality Monitor (EPQM)
• AC Power Center (ACPC) Supervisor Card
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

1. Make sure the Junction Box #3 is racked properly. Field experience revealed many cases of Junctions Boxes not installed properly.
2. Flight deck effect:

   1. AC synoptic page is all magenta.
   2. DC synoptic page has magenta APU battery related info.
   3. On the EMS CDU, ACPC electrical loads are dashed.

3. Alternative fault confirmation:

   1. On EMS CDU 1, select Diagnostic mode.

      1. Select SYSTEM - CNTL key (page 1/3).
      2. Select lower left side key.
      3. Select lower right side key.

   2. On EMS CDU 1, select CIRCUIT BREAKER - SYS key and COUNTERS.

      1. ACPC IN=0=loss of communication from ACPC left microprocessor to EMS CDU 1
      2. PCDA OUT=0=loss of communication from EMS CDU 1 to ACPC, DCPC, SPDA 1, SPDA 2, SPDA 3, SPDA 4, EMS CDU 2
         

1. Swap EMS CDU 1 with EMS CDU 2.

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

2. Swap ACPC microprocessor cards.

   1. If system checks are good, replace defective ACPC microprocessor card and do close out.
   2. If fault remains, continue with next step.

3. Replace ACPC supervisor card.

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

- For EMI Filter/Wiring check
4. Remove both microprocessor cards.
5. Perform wiring checks between EMS CDU, JB3 and ACPC.

   1. If wiring checks are not good, repair defective wiring as required and do close out.
   2. If wiring checks are good, continue with next step.

6. Perform wiring checks between ACPC connectors and microprocessors.

   1. If wiring checks are not good, repair defective wiring as required and do close out.
   2. If wiring checks are good, continue with next step.
      CAUTION: To prevent damage to the ACPC motherboard connectors, ensure that the wire jumper pin outside diameter (OD)/socket inside diameter (ID) does not exceed 0.025 inch.

7. Replace EMS CDU.

   1. If system checks good, do close out.
   2. If fault remains, continue with next step.

8. Swap ACPC.

   1. If system checks good, replace defective ACPC and do close out.
   2. If fault remains, continue with next step.

9. Replace JB3.

   1. If system checks good, do close out.
   2. If fault remains, continue with next step.

- For ACPC Data Bus check
10. Make sure that the EXT AC cord is not connected to the aircraft.
11. Remove one of fifteen SSPC cards one at a time and set Battery Master Switch to ON to determine faulty SSPC.
    NOTE: Monitor the fault via the AC Synoptic page or the Counters (EMS CDU Diagnostic Mode).
12. Replace defective SSPC.

    1. If system checks good, do close out.
    2. If fault remains, continue with next step.

13. Remove one of three PLC cards one at a time and set Battery Master Switch to ON to determine faulty PLC.
14. Replace defective PLC.

    1. If system checks good, do close out.
    2. If fault remains, continue with next step.

15. Remove one of four SLC cards one at a time and set Battery Master Switch to ON to determine faulty SLC.
16. Replace defective SLC.

    1. If system checks good, do close out.
    2. If fault remains, continue with next step.

17. Replace EPQM.

    1. If system checks good, do close out.
    2. If fault remains, continue with next step.

18. Replace A/D converter card.

    1. If system checks good, do close out.
    2. If fault remains, continue with next step.

19. Replace ACPC.
20. Do close out.
    Detail Troubleshooting with pin assignment