W DOC AIRBUS | TSM A320F

Loss of the HMU Overspeed Governor - Engine 1 - Channel A

TASK 73-20-00-810-837-A
Loss of the HMU Overspeed Governor - Engine 1 - Channel A

1. Possible Causes
  • HMU-1 [4000KC1]
  • Main Fuel Pump (MFP)
  • ECU [4000KS]
  • J7 harness
  • HJ7 harness
2. Job Set-up Information
 A. Referenced Information
REFERENCE
DESIGNATION
AMM 71-00-00-710-003
Engine Automatic Start
AMM 73-11-10-000-001
Removal of the Fuel Pump and Filter Assembly
AMM 73-11-10-000-003
Removal of the Fuel Pump and Filter Assembly
AMM 73-11-10-400-001
Installation of the Fuel Pump and Filter Assembly
AMM 73-11-10-400-003
Installation of the Fuel Pump and Filter Assembly
AMM 73-21-10-000-001
Removal of the Hydromechanical Unit (HMU)
AMM 73-21-10-000-002
Removal of the Hydromechanical Unit (HMU)
AMM 73-21-10-400-001
Installation of the Hydromechanical Unit (HMU)
AMM 73-21-10-400-002
Installation of the Hydromechanical Unit (HMU)
AMM 73-21-50-000-006
Removal of J7 Harness
AMM 73-21-50-000-040
Removal of the HJ7 Harness for SAC Engines
AMM 73-21-50-210-001
Visual Inspection of the Wiring Harness
AMM 73-21-50-400-006
Installation of the J7 Harness
AMM 73-21-50-400-040
Installation of the HJ7 Harness for SAC Engines
AMM 73-21-60-000-001
Removal of the Electronic Control Unit (ECU)
AMM 73-21-60-400-001
Installation of the Electronic Control Unit (ECU)
3. Fault Confirmation
Subtask 73-20-00-710-096-A ** ON A/C NOT FOR ALL
A. Perfom an engine start AMM 71-00-00-710-003.
4. Fault Isolation
Subtask 73-20-00-810-088-B ** ON A/C NOT FOR ALL
A. This fault is generated if an Overspeed Governor (OSG) switch position fault is detected during an engine start. This fault can be caused by a failed switch in the HMU, an open or short circuit in the J7 harness, low fuel pressure to the HMU, or a failed main fuel pump shaft.
   (1) If the failure message HMU (OSG), J7 occurs during an engine start:
     (a) If the fault does not repeat:
  • no maintenance action is required.
   (2) If the failure message HMU (OSG), J7 is not confirmed after re-start, but is repetitive:
     (a) Disconnect the J7 harness from the HMU receptacle (HMU-A) (located in the left core compartment).
       1 Visually examine the HMU receptacle and the J7 harness connector for damaged pins, contamination and fuel wetting AMM 73-21-50-210-001.
         a If harness connector or HMU receptacle is damaged:
  • repair or replace as required.
         b If no damage is found:
  • reconnect the J7 harness.
     (b) If the HMU part number is 8061-512 (GE SPEC 1348M79P07):
       1 If the fault continues during the subsequent flights:
       2 If the fault continues during the subsequent flights:
       3 If the fault continues during the subsequent flights:
     (c) If the HMU part number is 8061-526 (GE SPEC 1348M79P08) or higher:
       1 Inspect main fuel pump shaft.
         a If damaged/broken or worn:
         b If not damaged/broken or worn:
         c If the fault continues during the subsequent flights:
         d If the fault continues during the subsequent flights:
   (3) If the failure message HMU (OSG), J7 is confirmed:
     (a) If the HMU part number is 8061-512 (GE SPEC 1348M79P07):
       1 Inspect main fuel pump shaft.
         a If damaged/broken or worn:
         b If not damaged/broken or worn:
       2 If the fault continues during the subsequent flights:
       3 If the fault continues during the subsequent flights:
     (b) If the HMU part number is 8061-526 (GE SPEC 1348M79P08) or higher:
  • disconnect the J7 harness from the HMU receptacle (HMU-A) (located in the left core compartment)
  • visually examine the HMU receptacle and the J7 harness connector for damaged pins or contamination AMM 73-21-50-210-001.
       1 If harness connector or HMU receptacle is damaged:
  • repair or replace as required.
       2 If no damage is found:
  • do an electrical resistance test through the HMU receptacle between:
    . pins 21 and 41 (< 5 ohms)
    . pins 21 and 8 (> 10 megohms)
    . pin 21 and the ground (> 10 megohms).
         a If the resistance values are out of the specified limits:
         b If the resistance values are in the specified limits:
  • reconnect the J7 harness
  • disconnect the J7 harness from the ECU (4000KS) receptacle
  • visually examine the ECU (4000KS) receptacle and the J7 harness connector for damaged pins or contamination AMM 73-21-50-210-001.
         c If harness connector or ECU receptacle is damaged:
  • repair or replace as required.
         d If no damage is found:
  • do an electrical resistance test through the HMU receptacle between:
    . pins 21 and 41 (< 5 ohms)
    . pins 21 and 8 (> 10 megohms)
    . pin 21 and the ground (> 10 megohms).
         e If the resistance values are in the specified limits:
         f If the resistance values are out of the specified limits:
       3 If the fault continues during the subsequent flights:
         a If damaged/broken or worn:
         b If not damaged/broken or worn:
Subtask 73-20-00-810-088-C ** ON A/C NOT FOR ALL
A. This fault is generated if an Overspeed Governor (OSG) switch position fault is detected during an engine start. This fault can be caused by a failed switch in the HMU, an open or short circuit in the HJ7 harness, low fuel pressure to the HMU, or a failed main fuel pump shaft.
   (1) If the failure message HMU (OSG), J7 occurs during an engine start:
     (a) If the fault does not repeat:
  • no maintenance action is required.
   (2) If the failure message HMU (OSG), J7 is not confirmed after re-start, but is repetitive:
     (a) Disconnect the HJ7 harness from the HMU receptacle (HMU-A) (located in the left core compartment).
       1 Visually examine the HMU receptacle and the HJ7 harness connector for damaged pins, contamination and fuel wetting AMM 73-21-50-210-001.
         a If harness connector or HMU receptacle is damaged:
  • repair or replace as required.
         b If no damage is found:
  • reconnect the HJ7 harness.
     (b) If the HMU part number is 8061-512 (GE SPEC 1348M79P07):
       1 If the fault continues during the subsequent flights:
       2 If the fault continues during the subsequent flights:
       3 If the fault continues during the subsequent flights:
     (c) If the HMU part number is 8061-526 (GE SPEC 1348M79P08) or higher:
       1 Inspect main fuel pump shaft.
         a If damaged/broken or worn:
         b If not damaged/broken or worn:
         c If the fault continues during the subsequent flights:
         d If the fault continues during the subsequent flights:
   (3) If the failure message HMU (OSG), J7 is confirmed:
     (a) If the HMU part number is 8061-512 (GE SPEC 1348M79P07):
       1 Inspect main fuel pump shaft.
         a If damaged/broken or worn:
         b If not damaged/broken or worn:
       2 If the fault continues during the subsequent flights:
       3 If the fault continues during the subsequent flights:
     (b) If the HMU part number is 8061-526 (GE SPEC 1348M79P08) or higher:
  • disconnect the HJ7 harness from the HMU receptacle (HMU-A) (located in the left core compartment)
  • visually examine the HMU receptacle and the HJ7 harness connector for damaged pins or contamination AMM 73-21-50-210-001.
       1 If harness connector or HMU receptacle is damaged:
  • repair or replace as required.
       2 If no damage is found:
  • do an electrical resistance test through the HMU receptacle between:
    . pins 21 and 41 (< 5 ohms)
    . pins 21 and 8 (> 10 megohms)
    . pin 21 and the ground (> 10 megohms).
         a If the resistance values are out of the specified limits:
         b If the resistance values are in the specified limits:
  • reconnect the HJ7 harness
  • disconnect the HJ7 harness from the ECU (4000KS) receptacle
  • visually examine the ECU (4000KS) receptacle and the HJ7 harness connector for damaged pins or contamination AMM 73-21-50-210-001.
         c If harness connector or ECU receptacle is damaged:
  • repair or replace as required.
         d If no damage is found:
  • do an electrical resistance test through the HMU receptacle between:
    . pins 21 and 41 (< 5 ohms)
    . pins 21 and 8 (> 10 megohms)
    . pin 21 and the ground (> 10 megohms).
         e If the resistance values are in the specified limits:
         f If the resistance values are out of the specified limits:
       3 If the fault continues during the subsequent flights:
         a If damaged/broken or worn:
         b If not damaged/broken or worn:
Subtask 73-20-00-710-097-A ** ON A/C NOT FOR ALL
B. Do the test given in Para. 3.A.
   (1) No additional maintenance action is required if the fault is not confirmed.
   (2) Repeat the fault isolation procedure if the fault continues.
[Rev.8 from Aug 2018] 2026.04.04 04:35:17 UTC
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