EPSU - 28 VDC Fault Message

TASK 33-51-00-810-805-A
EPSU - 28 VDC Fault Message

1. Possible Causes

POWER-EMERGENCY SUPPLY [10WL]
wiring
EPSU [11WL]
EPSU [12WL]
EPSU [13WL]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 33-51-00-710-001	Operational Test of the Emergency Lights
ASM 335101
ASM 335102
AMM 33-51-38-000-001	Removal of the Emergency Power-Supply Unit (EPSU)
AMM 33-51-38-400-001	Installation of the Emergency Power-Supply Unit (EPSU)

3. Fault Confirmation

CAUTION: DO NOT USE THE TEACH-IN PROCEDURE AS AN ALTERNATIVE FOR TROUBLESHOOTING. A TEACH-IN PROCEDURE IS NOT A RESET PROCEDURE. BEFORE YOU DO A TEACH-IN PROCEDURE, MAKE SURE THAT YOU CORRECTED ALL FAILURES. IF YOU DO NOT OBEY THIS, FAILURES CAN CAUSE A MALFUNCTION OF THE CABIN EMERGENCY LIGHTING SYSTEM.

Subtask 33-51-00-710-058-A ** ON A/C NOT FOR ALL

A. Test
(1) Do the operational test of the emergency lighting system AMM 33-51-00-710-001.

4. Fault Isolation
Subtask 33-51-00-810-054-A ** ON A/C NOT FOR ALL

A. If the operational test gives the maintenance message:
(1) EPSU 28 VDC FWD L:

do a check for 28 VDC at the POWER SUPPLY UNIT-EMERGENCY (10WL).

(a) If there is 28 VDC:

replace the POWER-EMERGENCY SUPPLY [10WL] AMM 33-51-38-000-001 and AMM 33-51-38-400-001.

(b) If there is no 28 VDC:

do a check and repair the wiring between:
POWER SUPPLY UNIT-EMERGENCY (10WL) pin V and CB 2WL,
POWER SUPPLY UNIT-EMERGENCY (10WL) pin U and GND ASM 335101 and ASM 335102.

(2) EPSU 28 VDC EMER L:

do a check for 28 VDC at the POWER SUPPLY UNIT-EMERGENCY (11WL).

(a) If there is 28 VDC:

replace the EPSU [11WL] AMM 33-51-38-000-001 and AMM 33-51-38-400-001.

(b) If there is no 28 VDC:

do a check and repair the wiring between:
POWER SUPPLY UNIT-EMERGENCY (11WL) pin V and CB 1WL,
POWER SUPPLY UNIT-EMERGENCY (11WL) pin U and GND ASM 335101 and ASM 335102.

(3) EPSU 28 VDC EMER R:

do a check for 28 VDC at POWER SUPPLY UNIT-EMERGENCY (12WL).

(a) If there is 28 VDC:

replace the EPSU [12WL] AMM 33-51-38-000-001 and AMM 33-51-38-400-001.

(b) If there is no 28 VDC:

do a check and repair the wiring between:
POWER SUPPLY UNIT-EMERGENCY (12WL) pin V and CB 2WL,
POWER SUPPLY UNIT-EMERGENCY (12WL) pin U and GND ASM 335101 and ASM 335102.

(4) EPSU 28 VDC AFT L:

do a check for 28 VDC at POWER SUPPLY UNIT-EMERGENCY (13WL).

(a) If there is 28 VDC:

replace the EPSU [13WL] AMM 33-51-38-000-001 and AMM 33-51-38-400-001.

(b) If there is no 28 VDC:

do a check and repair the wiring between:
POWER SUPPLY UNIT-EMERGENCY (13WL) pin V and CB 1WL,
POWER SUPPLY UNIT-EMERGENCY (13WL) pin U and GND ASM 335101 and ASM 335102.

Subtask 33-51-00-710-059-A ** ON A/C NOT FOR ALL

B. Do the test as given in the Para. 3.A.

5. Close-up
Subtask 33-51-00-860-068-A ** ON A/C NOT FOR ALL

A. Put the aircraft back to its initial configuration.

[Rev.8 from Aug 2018] 2026.04.04 04:32:07 UTC