W DOC AIRBUS | TSM A320F

Failure of the MCDU3

TASK 31-32-00-810-922-A
Failure of the MCDU3

1. Possible Causes
  • MCDU-3 [3CA3]
  • RELAY-L/G POSITION, SYS1 (11GB)
  • LGCIU-1 [5GA1]
  • RELAY-GND SERVICE BUS CHG OVER [53GA]
  • wiring
  • C/B-DUMMY CB [11CA3]
2. Job Set-up Information
 A. Referenced Information
REFERENCE
DESIGNATION
AMM 22-82-12-000-001
Removal of the MCDU
AMM 22-82-12-400-002
Installation of the MCDU
ASM 228402
AMM 31-32-00-740-003
Ground Scanning of the CFDIU
ASM 323105
AMM 32-31-71-000-001
Removal of the LGCIU
AMM 32-31-71-400-001
Installation of the LGCIU
ASM 326201
3. Fault Confirmation
Subtask 31-32-00-740-288-A
A. Test
Do the ground scanning of the CFDIU AMM 31-32-00-740-003.
4. Fault Isolation
Subtask 31-32-00-810-171-A
A. If the test gives the maintenance message MCDU3 and the circuit breaker (11CA3) is closed:
  • do a check for 115VAC at the MCDU3 (3CA3).
   (1) If there is 115VAC:
   (2) If there is no 115VAC:
  • replace the RELAY-L/G POSITION, SYS1 (11GB).
     (a) If the fault continues:
       1 If the fault continues:
  • replace the RELAY-GND SERVICE BUS CHG OVER [53GA] .
         a If the fault continues:
  • do a check of the wiring from the relay (11GB):
    . pin A/C1 to MCDU3 (3CA3) pin A/40
    . pin A/C2 to the circuit breaker (11CA3)
    . pin A/X1 to relay (53GA) pin A/B2
    . pin A/X2 to LGCIU (5GA1) pin AB/1.
    * If there is no continuity:
    repair the related wiring.
    * If there is continuity:
    replace the C/B-DUMMY CB [11CA3] ASM 228402 ASM 323105 ASM 326201.
Subtask 31-32-00-810-172-A
B. If the test gives the maintenance message MCDU3 and the circuit breaker (11CA3) is open:
  • close this circuit breaker.
   (1) If this circuit breaker trips:
  • disconnect these two units:
    MCDU3 (3CA3)
    Relay (11GB)
  • close the circuit breaker (11CA3).
     (a) If this circuit breaker stays closed:
     (b) If this circuit breaker trips again:
  • do a check for a short to ground between the circuit breaker (11CA3) and the two units ASM 228402.
       1 If there is a short to ground:
  • repair the related wiring.
       2 If there is no short to ground:
  • replace the C/B-DUMMY CB [11CA3] .
Subtask 31-32-00-740-289-A
C. Do the test given in Para. 3.
[Rev.8 from Aug 2018] 2026.04.04 04:29:58 UTC
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