A. Perfom an engine start (Ref. AMM TASK 71-00-00-710-003). F 『
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4. Fault Isolation
_______________
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:
- restart the engine to confirm the fault (Ref. AMM TASK 71-00-00-710-003).
(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 R (Ref. AMM TASK 73-21-50-210-002).
a If harness connector or HMU receptacle is damaged:
_
- repair or replace as required.
b If no damage is found:
_ R - clean the connector and receptacle with a bristle brush R and stoddard solvent (Material No. CP2011) (Ref. AMM TASK R 73-21-50-210-002).
- reconnect the J7 harness.
(b) If the HMU part number is 8061-512 (GE SPEC 1348M79P07):
- replace the main fuel pump (Ref. AMM TASK 73-11-10-000-001) and (Ref. AMM TASK 73-11-10-400-001).
1 If the fault continues during the subsequent flights:
_
- replace the Hydromechanical Unit (HMU) (Ref. AMM TASK 73-21-10-000-001) and (Ref. AMM TASK 73-21-10-400-001).
2 If the fault continues during the subsequent flights:
_
- replace the ECU (4000KS) (Ref. AMM TASK 73-21-60-000-001) and (Ref. AMM TASK 73-21-60-400-001).
3 If the fault continues during the subsequent flights:
_
- replace the J7 harness (Ref. AMM TASK 73-21-50-000-006) and (Ref. AMM TASK 73-21-50-400-006).
(c) If the HMU part number is 8061-526 (GE SPEC 1348M79P08) or higher:
- remove the HMU (Ref. AMM TASK 73-21-10-000-001).
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1 Inspect main fuel pump shaft.
_ a If damaged/broken or worn:
_
- replace the Main Fuel Pump (MFP) (Ref. AMM TASK 73-11-10-000-001) and (Ref. AMM TASK 73-11-10-400-001).
b If not damaged/broken or worn:
_
- replace the HMU (Ref. AMM TASK 73-21-10-000-001) and (Ref. AMM TASK 73-21-10-400-001).
c If the fault continues during the subsequent flights:
_
- replace the ECU (4000KS) (Ref. AMM TASK 73-21-60-000-001) and (Ref. AMM TASK 73-21-60-400-001).
d If the fault continues during the subsequent flights:
_
- replace the J7 harness (Ref. AMM TASK 73-21-50-000-006) and (Ref. AMM TASK 73-21-50-400-006).
(3) If the failure message HMU (OSG), J7 is confirmed:
(a) If the HMU part number is 8061-512 (GE SPEC 1348M79P07):
- remove the HMU (Ref. AMM TASK 73-21-10-000-001).
1 Inspect main fuel pump shaft.
_ a If damaged/broken or worn:
_
- replace the main fuel pump (Ref. AMM TASK 73-11-10-000-001) and (Ref. AMM TASK 73-11-10-400-001).
b If not damaged/broken or worn:
_
- replace the HMU (Ref. AMM TASK 73-21-10-000-001) and (Ref. AMM TASK 73-21-10-400-001).
2 If the fault continues during the subsequent flights:
_
- replace the ECU (4000KS) (Ref. AMM TASK 73-21-60-000-001) and (Ref. AMM TASK 73-21-60-400-001).
3 If the fault continues during the subsequent flights:
_
- replace the J7 harness (Ref. AMM TASK 73-21-50-000-006) and (Ref. AMM TASK 73-21-50-400-006).
(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 R connector for damaged pins or contamination (Ref. AMM TASK 73-R 21-50-210-002).
1 If harness connector or HMU receptacle is damaged:
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