R NOTE : As the APU GEN was set to OFF because of a true failure, the fault
____ R confirmation is not necessary.
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R 4. Fault Isolation
_______________
R A. If the fault symptom is identified by the upper ECAM-DU warning APU GEN R FAULT and one of these two CMS messages: R DELTA CURRENT GEN APU CHANNEL or R OVERCURRENT GEN APU CHANNEL
R NOTE : This CFDS messages can come into view with other CFDS messages
____ R related to a delta current or an overcurrent condition of one of R the generator channels 1 or 2.
R - do the trouble shooting procedure related to the delta current or the R overcurrent condition messages.
R NOTE : When you do the trouble shooting for the CFDS message DELTA
____ R CURRENT GEN APU CHANNEL or OVERCURRENT GEN APU CHANNEL, you can R remove one after the other the GCU 1 and the GCU 2 from their R position in the forward avionics rack 90VU to isolate the main AC R buses 1XP and 2XP.
R (1) If the fault continues:
R - do a check of the feeders (Ref. ASM 24-23/01) for a short circuit
R or a short to ground between:
R . feeder A pin L1 of the APU generator AC current transformer R (42XS) and pin A/F of the APU GLC (3XS)
R . feeder B pin L2 of the APU generator AC current transformer and R pin A/E of the APU GLC
R . feeder C pin L3 of the APU generator AC current transformer and R pin A/D of the APU GLC.
R (a) If the feeders are not correct:
R - repair or replace the feeders as necessary.
R (b) If the feeders are correct:
R - do a check and repair the feeders between the APU GLC (3XS),
R the EPC (3XG), the BTC 1 (11XU1) and the BTC 2 (11XU2) (Ref.
R ASM 24-22/02), (Ref. ASM 24-22/03) and (Ref. ASM 24-41/01).
R B. Open, safety and tag this(these) circuit breaker(s):
R -------------------------------------------------------------------------------R PANEL DESIGNATION IDENT. LOCATION
R -------------------------------------------------------------------------------R 122VU ELEC/GCU/2 2XU2 T27
R C. If the feeders are correct:
R - loosen and lower the nuts that attach the GCU 2 and pull it from the
R forward electronics rack 90VU to disconnect the electrical connectors
R - energize the aircraft electrical circuits from the APU (Ref. AMM TASK
R 24-41-00-861-002)
R - after five minutes, see if there is a trip.
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R (1) If there is a trip:
R - de-energize the aircraft electrical circuits from the APU (Ref. AMM
R TASK 24-41-00-862-002)
R - do the trouble shooting of the generator 1 channel (Ref. TASK 24-
R 20-00-810-862).
R (2) If there is no trip:
R - push the GCU 2 on its rack to connect the electrical connectors and
R engage the nuts on the lugs and tighten. Then on the rear circuit
R breaker panel 122VU, remove the safety clip and tag and close the
R circuit breaker 2XU2
R - after five minutes, see if there is a trip.
R (a) If there is a trip:
R - de-energize the aircraft electrical circuits from the APU (Ref.
R AMM TASK 24-41-00-862-002)
R - do the trouble shooting of the generator 2 channel (Ref. TASK
R 24-20-00-810-863).
R D. Make sure that the aircraft electrical circuits operate correctly in APU
R configuration.
R (1) Make sure that the GCU 1 and the GCU 2 are correctly installed on
R their forward electronics rack 90VU.
R (2) On the rear circuit breaker panel 122VU, make sure that the circuit
R breakers 2XU1 and 2XU2 are closed (if the circuit breakers are not
R closed, remove the safety clips and tags and close them).
R (3) Energize the aircraft electrical circuits from the APU (Ref. AMM TASK
R 24-41-00-861-002).
R (4) Let the APU generator operate for five minutes to make sure that it
R operates correctly.
R (5) De-energize the aircraft electrical circuits from the APU (Ref. AMM
R TASK 24-41-00-862-002).
