Loss of the 28VDC Supply of the BSCU SYS 1

TASK 32-42-00-810-828-A
Loss of the 28VDC Supply of the BSCU SYS 1

1. Possible Causes

BSCU [10GG]
wiring from the BSCU (10GG) pin AB/15K to the ground terminal
SW-A/SKID & NW STRG (5GG)
wiring from the BSCU (10GG) to the switch (5GG)
wiring from the switch (5GG) pin 1E to the circuit breaker (2GG)
C/B-HYDRAULIC/BRAKING AND STEERING/SYS1/IND AND/SPLY [2GG]
ABCU [95GG]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
SPM 205221
SPM 205222
ASM 324201
SPM 324201
AMM 32-42-21-000-001	Removal of the Normal-Brake Pressure Transducer
AMM 32-42-21-400-001	Installation of the Normal-Brake Pressure Transducer
AMM 32-42-34-000-001	Removal of the Braking/Steering Control Unit (BSCU)
AMM 32-42-34-400-001	Installation of the Braking/Steering Control Unit (BSCU)
AMM 32-43-34-000-001	Removal of the Alternate Braking Control Unit (ABCU)
AMM 32-43-34-400-001	Installation of the Alternate Braking Control Unit (ABCU)
AMM 32-46-00-740-001	BITE Test of the BSCU
AMM 33-14-33-000-001	Removal of the Annunciator-Light Test and Interface-Board
AMM 33-14-33-400-001	Installation of the Annunciator-Light Test and Interface-Board

3. Fault Confirmation
Subtask 32-42-00-740-074-A

A. Test
(1) Not applicable

4. Fault Isolation
Subtask 32-42-00-865-050-A

A. Make sure that this(these) circuit breaker(s) is(are) closed:

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C ALL
121VU	HYDRAULIC/BRAKING AND STEERING/SYS1/IND AND/SPLY	2GG	M33

Subtask 32-42-00-810-214-A

B. Test
(1) Do a reset of the BSCU with the A/SKID AND NOSE WHEEL switch (5GG).
(2) Do the BITE test of the BSCU with the BSCU channel that is the source of the fault message AMM 32-46-00-740-001.
(3) Do a check of the status of the circuit breaker (2GG).

Subtask 32-42-00-810-079-A

C. If the circuit breaker (2GG) is closed:

Do a check for 28VDC at pin AB/14K of the BSCU (10GG) ASM 324201.

(1) If there is 28VDC:

Replace the BSCU [10GG] AMM 32-42-34-000-001 and AMM 32-42-34-400-001.

(2) If there is no 28VDC:

Do a check for a ground signal at pin AB/15K of the BSCU (10GG) ASM 324201.

(a) If there is no ground signal:

Repair the wiring from the BSCU (10GG) pin AB/15K to the ground terminal ASM 324201.

(b) If there is a ground signal:

Replace the SW-A/SKID & NW STRG (5GG) ASM 324201.

1 If the fault continues:

Do a check and repair the wiring from the BSCU (10GG) to the switch (5GG), pin AB/14K to pin 2E ASM 324201.
Do a check and repair the wiring from the switch (5GG) pin 1E to the circuit breaker (2GG) ASM 324201.

2 If the fault continues:

Replace the C/B-HYDRAULIC/BRAKING AND STEERING/SYS1/IND AND/SPLY [2GG] ASM 324201.

3 If the fault continues:

Replace the ABCU [95GG] AMM 32-43-34-000-001 and AMM 32-43-34-400-001.

Subtask 32-42-00-810-080-A

D. If the circuit breaker (2GG) is open:
(1) Remove the BSCU (10GG) AMM 32-42-34-000-001.
(2) Disconnect the connector A of these units:

PRESS XDCR-NORM BRK WHEEL 2 (13GG)
PRESS XDCR-NORM BRK WHEEL 3 (12GG) AMM 32-42-21-000-001.

(3) Disconnect the connector A of this unit:

RELAY-WHEEL 1 SPEED (25GG).

(4) Disconnect the connector A of this unit:

SW-A/SKID & NW STRG (5GG)

(5) Disconnect the connector A of this unit:

BOARD-ANN LT TEST & INTFC (1LP) AMM 33-14-33-000-001.

(6) Do a check for a short circuit of the wiring between the BSCU, PRESS XDCR-NORM, SW-A/SKID & NW STRG, RELAY-WHEEL 1 SPEED and BOARD-ANN LT TEST & INTFC (1LP) BRK WHEEL SPM 205221, SPM 205222, SPM 324201.
(a) If there is a short circuit:
1 Repair the wiring.
2 Connect the connector A of this unit:

BOARD-ANN LT TEST & INTFC (1LP) AMM 33-14-33-000-001.

3 Connect the connector A of this unit:

SW-A/SKID & NW STRG (5GG).

4 Connect the connector A of this unit:

RELAY-WHEEL 1 SPEED (25GG).

5 Connect the electrical connector A of these units.

PRESS XDCR-NORM BRK WHEEL 2 (13GG)
PRESS XDCR-NORM BRK WHEEL 3 (12GG) AMM 32-42-21-400-001.

6 Install the BSCU (10GG) AMM 32-42-34-400-001.
(b) If there is no short circuit:
1 Close the circuit breaker (2GG).
(7) If the circuit breaker (2GG) stays closed:
(a) Connect the units one after the other and if the circuit breaker (2GG) trips again, replace the related unit:

For the BSCU (10GG) AMM 32-42-34-000-001 and AMM 32-42-34-400-001
For the pressure transducer (12GG) AMM 32-42-21-000-001 and AMM 32-42-21-400-001
For the pressure transducer (13GG) AMM 32-42-21-000-001 and AMM 32-42-21-400-001
For the relay (25GG) ASM 324201
For the switch (5GG) ASM 324201
For the board (1LP) AMM 33-14-33-000-001 and AMM 33-14-33-400-001.

(b) Connect all the units.
(8) If the fault continues:

Replace the C/B-HYDRAULIC/BRAKING AND STEERING/SYS1/IND AND/SPLY [2GG] ASM 324201.

Subtask 32-42-00-740-075-A

E. After the subsequent flight, make sure that the fault does not continue.

[Rev.8 from Aug 2018] 2026.04.04 04:31:32 UTC