DOC AIRBUS | TSM A320FAPU Master Switch Fault on EIU-1
TASK 73-25-01-810-829-A
APU Master Switch Fault on EIU-1
1. Possible Causes
2. Job Set-up Information
A. Fixtures, Tools, Test and Support Equipment
B. Referenced Information
3. Fault Confirmation
Subtask 73-25-01-710-078-A ** ON A/C NOT FOR ALL
Subtask 73-25-01-810-086-A ** ON A/C NOT FOR ALL
Subtask 73-25-01-860-078-A ** ON A/C NOT FOR ALL
[Rev.8 from Aug 2018]
2026.04.04 04:36:56 UTC
APU Master Switch Fault on EIU-1
1. Possible Causes
2. Job Set-up Information
A. Fixtures, Tools, Test and Support Equipment
| REFERENCE | QTY | DESIGNATION |
|---|---|---|
| No specific | 1 | MULTIMETER - STANDARD |
| REFERENCE | DESIGNATION |
|---|---|
| AWM 496101 | |
| AWM 496102 | |
| AMM 73-25-34-000-802 | Removal of the Engine Interface Unit (EIU) |
| AMM 73-25-34-400-802 | Installation of the Engine Interface Unit (EIU) |
| AMM 73-25-34-710-802 | Operational Test of the Engine Interface Unit (EIU) with the Centralized Fault Display System (CFDS) |
| AMM 73-25-34-860-806 | Engine Interface Unit (EIU) DISCRETE INPUTS Menu Data Status |
| AWM 732561 |
Subtask 73-25-01-710-078-A ** ON A/C NOT FOR ALL
A. Do as follows:
(1) On overhead panel 25VU:
(a) Make sure that AVAIL and ON legend of APU START pushbutton switch are off.
(b) Press the APU MASTER SW pushbutton switch.
(2) Do the operational test of the Engine Interface Unit (EIU) with the Centralized Fault Display System (CFDS) to confirm this fault AMM 73-25-34-710-802.
(3) On overhead panel 25VU:
(a) Release the APU MASTER SW pushbutton switch.
(4) Do the operational test of the EIU with the CFDS to confirm this fault AMM 73-25-34-710-802.
4. Fault Isolation(1) On overhead panel 25VU:
(a) Make sure that AVAIL and ON legend of APU START pushbutton switch are off.
(b) Press the APU MASTER SW pushbutton switch.
(2) Do the operational test of the Engine Interface Unit (EIU) with the Centralized Fault Display System (CFDS) to confirm this fault AMM 73-25-34-710-802.
(3) On overhead panel 25VU:
(a) Release the APU MASTER SW pushbutton switch.
(4) Do the operational test of the EIU with the CFDS to confirm this fault AMM 73-25-34-710-802.
Subtask 73-25-01-810-086-A ** ON A/C NOT FOR ALL
A. If there is confirmation of the fault:
(1) On overhead panel 25 VU, press the APU MASTER SW pushbutton switch.
(2) Check the status of EIU-1 (1KS1) Discrete Input (DSI) for APU MASTER SW ON AMM 73-25-34-860-806.
(a) Check that the status of APU MASTER SW ON is 1
(b) If the status is not 1:
1 Remove EIU-1 (1KS1) AMM 73-25-34-000-802.
2 Use a MULTIMETER - STANDARD to do a check of the wiring between contact 3B of EIU-1 (1KS1) and ground (2405VT) for continuity AWM 732561 and AWM 496101.
3 If continuity is OK, replace P/BSW-APU/MASTER SW [14KD] .
4 If continuity is not OK, replace wiring as necessary AWM 732561 and AWM 496101.
5 Install EIU-1 (1KS1) AMM 73-25-34-400-802.
6 Do the test given in Para. 3.
(c) If the status is 1 or if the fault continues, go to next step.
(3) Check the status of EIU-1 (1KS1) DSI for APU MASTER SW OFF AMM 73-25-34-860-806:
(a) Check that the status of APU MASTER SW OFF is 0.
(b) If the status is not 0:
1 Remove EIU-1 (1KS1) AMM 73-25-34-000-802.
2 Check wiring between contact 3C of EIU-1 (1KS1) and APU MASTER SW (14KD) for short to ground AWM 732561, AWM 496102 and AWM 496101.
3 If wiring is OK, replace P/BSW-APU/MASTER SW [14KD] .
4 If wiring is not OK, replace wiring as necessary AWM 732561, AWM 496102 and AWM 496101.
5 Install EIU-1 (1KS1) AMM 73-25-34-400-802.
6 Do the test given in Para. 3.
(c) If the status is 0 or if the fault continues, go to next step.
(4) On overhead panel 25 VU, release the APU MASTER SW pushbutton switch.
(5) Check the status of EIU-1 (1KS1) DSI for APU MASTER SW OFF AMM 73-25-34-860-806.
(a) Check that the status of APU MASTER SW OFF is 1.
(b) If the status is not 1:
1 Remove EIU-1 (1KS1) AMM 73-25-34-000-802.
2 Check wiring between contact 3C of EIU-1 (1KS1) and ground (2405VT) for continuity AWM 732561, AWM 496102 and AWM 496101.
3 If continuity is OK, replace P/BSW-APU/MASTER SW [14KD] .
4 If continuity is not OK, replace wiring as necessary AWM 732561, AWM 496102 and AWM 496101.
5 Install EIU-1 (1KS1) AMM 73-25-34-400-802.
6 Do the test given in Para. 3.
(c) If the status is 1 or if the fault continues, go to next step.
(6) Check the status of EIU-1 (1KS1) DSI for APU MASTER SW ON AMM 73-25-34-860-806.
(a) Check that the status of APU MASTER SW ON is 0.
(b) If the status is not 0:
1 Remove EIU-1 (1KS1) AMM 73-25-34-000-802.
2 Check wiring between contact 3B of EIU-1 (1KS1) and APU MASTER SW (14KD) for short to ground AWM 732561 and AWM 496101.
3 If wiring is OK, replace P/BSW-APU/MASTER SW [14KD] .
4 If wiring is not OK, replace wiring as necessary AWM 732561 and AWM 496101.
5 Install EIU-1 (1KS1) AMM 73-25-34-400-802.
6 Do the test given in Para. 3.
(c) If the status is 0 or if the fault continues, go to next step.
(d) If all statuses are OK or if the fault continues:
1 Replace EIU-1 [1KS1] AMM 73-25-34-000-802 and AMM 73-25-34-400-802.
5. Close-up(1) On overhead panel 25 VU, press the APU MASTER SW pushbutton switch.
(2) Check the status of EIU-1 (1KS1) Discrete Input (DSI) for APU MASTER SW ON AMM 73-25-34-860-806.
(a) Check that the status of APU MASTER SW ON is 1
(b) If the status is not 1:
1 Remove EIU-1 (1KS1) AMM 73-25-34-000-802.
2 Use a MULTIMETER - STANDARD to do a check of the wiring between contact 3B of EIU-1 (1KS1) and ground (2405VT) for continuity AWM 732561 and AWM 496101.
3 If continuity is OK, replace P/BSW-APU/MASTER SW [14KD] .
4 If continuity is not OK, replace wiring as necessary AWM 732561 and AWM 496101.
5 Install EIU-1 (1KS1) AMM 73-25-34-400-802.
6 Do the test given in Para. 3.
(c) If the status is 1 or if the fault continues, go to next step.
(3) Check the status of EIU-1 (1KS1) DSI for APU MASTER SW OFF AMM 73-25-34-860-806:
(a) Check that the status of APU MASTER SW OFF is 0.
(b) If the status is not 0:
1 Remove EIU-1 (1KS1) AMM 73-25-34-000-802.
2 Check wiring between contact 3C of EIU-1 (1KS1) and APU MASTER SW (14KD) for short to ground AWM 732561, AWM 496102 and AWM 496101.
3 If wiring is OK, replace P/BSW-APU/MASTER SW [14KD] .
4 If wiring is not OK, replace wiring as necessary AWM 732561, AWM 496102 and AWM 496101.
5 Install EIU-1 (1KS1) AMM 73-25-34-400-802.
6 Do the test given in Para. 3.
(c) If the status is 0 or if the fault continues, go to next step.
(4) On overhead panel 25 VU, release the APU MASTER SW pushbutton switch.
(5) Check the status of EIU-1 (1KS1) DSI for APU MASTER SW OFF AMM 73-25-34-860-806.
(a) Check that the status of APU MASTER SW OFF is 1.
(b) If the status is not 1:
1 Remove EIU-1 (1KS1) AMM 73-25-34-000-802.
2 Check wiring between contact 3C of EIU-1 (1KS1) and ground (2405VT) for continuity AWM 732561, AWM 496102 and AWM 496101.
3 If continuity is OK, replace P/BSW-APU/MASTER SW [14KD] .
4 If continuity is not OK, replace wiring as necessary AWM 732561, AWM 496102 and AWM 496101.
5 Install EIU-1 (1KS1) AMM 73-25-34-400-802.
6 Do the test given in Para. 3.
(c) If the status is 1 or if the fault continues, go to next step.
(6) Check the status of EIU-1 (1KS1) DSI for APU MASTER SW ON AMM 73-25-34-860-806.
(a) Check that the status of APU MASTER SW ON is 0.
(b) If the status is not 0:
1 Remove EIU-1 (1KS1) AMM 73-25-34-000-802.
2 Check wiring between contact 3B of EIU-1 (1KS1) and APU MASTER SW (14KD) for short to ground AWM 732561 and AWM 496101.
3 If wiring is OK, replace P/BSW-APU/MASTER SW [14KD] .
4 If wiring is not OK, replace wiring as necessary AWM 732561 and AWM 496101.
5 Install EIU-1 (1KS1) AMM 73-25-34-400-802.
6 Do the test given in Para. 3.
(c) If the status is 0 or if the fault continues, go to next step.
(d) If all statuses are OK or if the fault continues:
1 Replace EIU-1 [1KS1] AMM 73-25-34-000-802 and AMM 73-25-34-400-802.
Subtask 73-25-01-860-078-A ** ON A/C NOT FOR ALL
A. Put the aircraft back to its initial configuration.
(1) Make sure that the work area is clean and clear of tools and other items.
(1) Make sure that the work area is clean and clear of tools and other items.