Message Name:

CDU 1/ACPC LEFT FTM-A20/WRG

Message Code:

2451370ACP

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) Microprocessor Card
• AC Power Center (ACPC) (A54)
• ACPC Supervisor Card
• Junction Box (JB3)/PCB3
• Associated Wiring

Advisory Wire/Service Bulletin: None.

Forum Articles/Infoservice/Newsletter: None

Flight Operation Notifications Manual (FONM): None

NOTES:

• Make sure the Junction Box #3 is racked properly. Field experience revealed many cases of Junctions Boxes not installed properly. 

1. 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.

2. Alternative Fault Confirmation And Data Gathering

   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. Take a picture.
      2. ACPC IN = 0 ( Zero indicates loss of communication from ACPC left microprocessor to EMS CDU 1).
      3. PCDA OUT= 0 (Zero indicates loss of communication from EMS CDU 1 to ACPC, DCPC, SPDA 1, SPDA 2, SPDA 3, SPDA 4, EMS CDU 2).

1. Interchange 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 the next step.

2. Interchange ACPC microprocessor cards. Is the fault present?

   1. If NO, replace defective ACPC microprocessor card and do close out.
   2. If YES, continue with next step.

3. Disconnect EMS CDU 1 connector A94P1. Remove both ACPC microprocessor cards.
   

   EMS CDU To ACPC Schematic

4. Do Wiring checks as follows:

   From	To	Expected Result	Result
   A94P1-5	Ground	Open
   A94P1-6	Ground	Open
   A94P1-7	Ground	Open
   A94P1-8	Ground	Open

5. Are results satisfactory?

   1. If YES, go to step 8.
   2. If NO, continue with the next step.

6. Disconnect ACPC connector A54P6. Do Wiring checks as follows:
   

   From	To	Expected Results	Result
   A94P1-5	Ground	Open
   A94P1-6	Ground	Open
   A94P1-7	Ground	Open
   A94P1-8	Ground	Open

7. Are results satisfactory?

   1. If YES, continue with the next step.
   2. If NO, repair defective wiring as required and do close out.

8. Perform a continuity check between the EMS CDU and the ACPC Microprocessor cards as follows:

   From	To	Result
   A94P1-5	P2A-23
   A94P1-6	P2B-23
   A94P1-7	P2A-22
   A94P1-8	P2B-22
   A94P1-7	P3A-22
   A94P1-8	P3B-22

   1. If there is continuity, replace ACPC Supervisor Card.
   2. If there is no continuity, continue with the next step.

9. Disconnect ACPC Connector A54P6. Perform a continuity check as follows:

   From	To	Result
   A94P1-5	A54P6-V
   A94P1-6	A54P6-W
   A94P1-7	A54P6-R
   A94P1-8	A54P6-S

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

10. Replace ACPC.
11. Do close out.