- disconnect the plug from the external power receptacle (20XG),

 - make sure that the ELEC/EXT PWR pushbutton switch (10XG) is in the ON position,

 - do a check of the external power plug for a short to 28VDC of the pin

 F.
 (1) If there is a short to 28VDC:

 - repair or replace the external power plug.

 (2) If there is no short to 28VDC:

 - do a check and repair the wiring of the external power interlock-control (Ref. ASM 24-41/01) for a short to 28VDC or a short circuit between: . pin F and pin E of the external power receptacle (20XG) . pin B/12E of the GAPCU and pin F of the external power receptacle (20XG).
 (a) If the fault continues:
 - replace the GAPCU (24XG) (Ref. AMM TASK 24-41-34-000-001) and (Ref. AMM TASK 24-41-34-400-001).
 B. Test
 (1) Energize the aircraft electrical circuits from the external power (Ref. AMM TASK 24-41-00-861-002).

 (2) De-energize the aircraft electrical circuits from the external power (Ref. AMM TASK 24-41-00-862-002).

 TASK 24-41-00-810-830
 Failure of the External Power Because of an Unbalance
 1. Possible Causes
_______________
 - feeders

 - external power

 2. Job Set-up Information
______________________
 A. Referenced Information
 -------------------------------------------------------------------------------REFERENCE DESIGNATION -------------------------------------------------------------------------------
AMM 24-41-00-861-002 Energize the Aircraft Electrical Circuits from the External Power AMM 24-41-00-862-002 De-energize the Aircraft Electrical Circuits Supplied
 from the External Power ASM 24-22/02 ASM 24-22/03 ASM 24-41/01
 3. Fault Confirmation
__________________
 A. Test
 (1) Energize the aircraft electrical circuits from the external power (Ref. AMM TASK 24-41-00-861-002).
 4. Fault Isolation
_______________
 A. If it is not possible to connect the external power source to the aircraft electrical network and if the fault symptom is identified by the CFDS message EXTERNAL POWER UNBALANCE:
 - do a check of the feeders for a short circuit or a short to ground (Ref. ASM 24-41/01), (Ref. ASM 24-22/02) and (Ref. ASM 24-22/03) between: . the external power receptacle (20XG) and the EPC (3XG) . the EPC and the primary circuit breakers of the AC main buses 1XP and 2XP through the BTC 1 (11XU1) and the BTC 2 (11XU2)

 - do a check of the status of the primary circuit breakers of the AC main buses 1XP and 2XP.

 (1) If the feeders are not correct or if the primary circuit breakers are open:

 - repair or replace the feeders as necessary

 - close or do a reset of the primary circuit breakers.

 (a) Energize the aircraft electrical circuits from the external power (Ref. AMM TASK 24-41-00-861-002).

 (2) If the feeders are correct or if the primary circuit breakers are closed:

 1_ If it is not possible to connect the external power source to
 the aircraft electrical network:
 - replace the external power.

 - replace the external power.
 B. Test
 (1) Energize the aircraft electrical circuits from the external power (Ref. AMM TASK 24-41-00-861-002).

 (2) De-energize the aircraft electrical circuits from the external power (Ref. AMM TASK 24-41-00-862-002).

R TASK 24-41-00-810-832 R Failure of the GAPCU in the FAILSAFE Mode R 1. Possible Causes
_______________ R - GAPCU (24XG) R 2. Job Set-up Information
______________________
R A. Referenced Information
R -------------------------------------------------------------------------------R REFERENCE DESIGNATION R -------------------------------------------------------------------------------
R AMM 24-41-00-740-002 R AMM 24-41-00-861-002 R R AMM 24-41-00-861-002 R R AMM 24-41-00-862-002 R R AMM 24-41-00-862-002 R R AMM 24-41-34-000-001 R R AMM 24-41-34-400-001 R
R 3. Fault Confirmation
__________________
R A. Test Operational Check of GAPCU via CFDS Energize the Aircraft Electrical Circuits from the External Power Energize the Aircraft Electrical Circuits from the APU De-energize the Aircraft Electrical Circuits Supplied from the External Power De-energize the Aircraft Electrical Circuits Supplied from the APU Removal of the Ground Auxiliary Power Control Unit (GAPCU) (24XG) Installation of the Ground Auxiliary Power Control Unit (GAPCU) (24XG)
R (1) Remove all AC and DC power from the GAPCU (24XG):
R - de-energize the aircraft electrical circuits from the APU (Ref. AMM
　
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