Loss of the Power Supply of the Engine 1 FDU (Loop A)

TASK 26-12-00-810-823-A
Loss of the Power Supply of the Engine 1 FDU (Loop A)

1. Possible Causes

FDU-ENG1 [2WD1]
wiring of the 28VDC signal from the circuit breaker 7WD1 to the engine 1 FDU
wiring of the ground signal at the engine 1 FDU
C/B-ENGINE/1/FIRE DET/LOOP A [7WD1]
ENG/APU FIRE PNL [1WD]
BOARD-ANN LT TEST & INTFC [5LP]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
TSM TASK 24-00-00-810-803-A	Circuit Breaker Tripped and/or C/B TRIPPED Warning
AMM 26-12-00-710-001	Operational Check of Loop/Squib
ASM 261201
AMM 26-12-12-000-001	Removal of the ENG/APU Fire Panel
AMM 26-12-12-400-001	Installation of the ENG/APU Fire Panel
AMM 26-12-34-000-001	Removal of the Engine Fire-Detection Unit (FDU)
AMM 26-12-34-400-001	Installation of the Engine Fire-Detection Unit (FDU)
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 26-12-00-710-092-A

A. Test
(1) Do the operational test of the engine fire and overheat detection (loop/squib) AMM 26-12-00-710-001.
(a) If the circuit breaker 7WD1 is open, refer to Para. 4.C.

4. Fault Isolation
Subtask 26-12-00-865-056-A

A. Table of the circuit breakers used in this procedure:

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C ALL
49VU	ENGINE/1/FIRE DET/LOOP A	7WD1	A06

Subtask 26-12-00-810-072-A

B. If the circuit breaker 7WD1 is closed, and if the FIRE legend of the ENG 1 annunciator and the DISCH legend of the ENG 1/AGENT 1 pushbutton switch on the ENG/APU FIRE panel do not come on:

do a check for 28VDC at the pin A/A of the engine 1 FDU.

(1) If there is 28VDC:

replace the FDU-ENG1 [2WD1] AMM 26-12-34-000-001 and AMM 26-12-34-400-001.

(2) If there is no 28VDC:

do a check of the wiring of the 28VDC signal from the circuit breaker 7WD1 to the engine 1 FDU

ASM 261201.
(a) If there is no continuity:

repair the above wiring.

(b) If there is continuity:

do a check of the wiring of the ground signal at the engine 1 FDU pin A/B

ASM 261201.
1 If there is no continuity:

repair the above wiring.

2 If there is continuity:

replace the C/B-ENGINE/1/FIRE DET/LOOP A [7WD1] .

Subtask 26-12-00-810-073-A

C. If the circuit breaker (7WD1) is open:

Do the procedure (Ref. TSM TASK 24-00-00-810-803).

(1) If the fault continues:

disconnect the three units below:
FDU-ENG1 [2WD1]
ENG/APU FIRE PNL [1WD]
BOARD-ANN LT TEST & INTFC [5LP]
close the C/B-ENGINE/1/FIRE DET/LOOP A [7WD1] .

(a) If the circuit breaker stays closed:

connect the units one by one until the circuit breaker trips
replace the defective unit:
.for LRU 2WD1: AMM 26-12-34-000-001 and AMM 26-12-34-400-001
.for LRU 1WD: AMM 26-12-12-000-001 and AMM 26-12-12-400-001
.for LRU 5LP: AMM 33-14-33-000-001 and AMM 33-14-33-400-001.

1 If the fault continues:

replace the C/B-ENGINE/1/FIRE DET/LOOP A [7WD1] .

(2) Connect all the units.

Subtask 26-12-00-710-093-A

D. Do the test given in Para. 3.

[Rev.8 from Aug 2018] 2026.04.04 04:27:09 UTC