- visually examine the HMU receptacle and the HJ7 harness connector for damaged pins or contamination (Ref. AMM TASK 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:
_
- replace the HMU (Ref. AMM TASK 73-21-10-000-002) and (Ref. AMM TASK 73-21-10-400-002).
b If the resistance values are in the specified limits:
_ - reconnect the HJ7 harness
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- 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 (Ref. AMM TASK 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:
_
- replace the ECU (4000KS) (Ref. AMM TASK 73-21-60-000-001) and (Ref. AMM TASK 73-21-60-400-001).
f If the resistance values are out of the specified limits:
_
- replace the HJ7 harness (Ref. AMM TASK 73-21-50-000-040) and (Ref. AMM TASK 73-21-50-400-040).
3 If the fault continues during the subsequent flights:
_
- remove the HMU (Ref. AMM TASK 73-21-10-000-002)
- inspect main fuel pump shaft.
a If damaged/broken or worn:
_
- replace the main fuel pump (Ref. AMM TASK 73-11-10-000-003) and (Ref. AMM TASK 73-11-10-400-003).
b If not damaged/broken or worn:
_
- replace the HMU (Ref. AMM TASK 73-21-10-000-002) and (Ref. AMM TASK 73-21-10-400-002).
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.
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TASK 73-20-00-810-838
Loss of the HMU Overspeed Governor - Engine 2 - Channel A
1. Possible Causes
_______________
R - Hydromechanical Unit (HMU)
- Main Fuel Pump (MFP)
- ECU (4000KS)
- HJ7 harness
2. Job Set-up Information
______________________
A. Referenced Information
-------------------------------------------------------------------------------REFERENCE DESIGNATION -------------------------------------------------------------------------------
AMM 71-00-00-710-003 Engine Automatic Start AMM 73-11-10-000-003 Removal of the Fuel Pump and Filter Assembly AMM 73-11-10-400-003 Installation of the Fuel Pump and Filter Assembly AMM 73-21-10-000-002 Removal of the Hydromechanical Unit (HMU) AMM 73-21-10-400-002 Installation of the Hydromechanical Unit (HMU) AMM 73-21-50-000-040 Removal of the HJ7 Harness AMM 73-21-50-210-001 Visual Inspection of the Wiring Harness AMM 73-21-50-400-040 Installation of the HJ7 Harness 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
__________________
A. Perfom an engine start (Ref. AMM TASK 71-00-00-710-003).
4. Fault Isolation
_______________
R A. This fault is generated if an Overspeed Governor (OSG) switch position R fault is detected during an engine start. This fault can be caused by a R failed switch in the HMU, an open or short circuit in the HJ7 harness, R low fuel pressure to the HMU, or a failed main fuel pump shaft.
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