SDCU/SMOKE DET LOOP FAULT

TASK 26-17-00-810-807-A
SDCU/SMOKE DET LOOP FAULT

1. Possible Causes

electrical connectors
wiring

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
ASM 261602
AMM 26-16-15-000-001	Removal of the Cargo-Compartment Smoke Detectors
AMM 26-16-15-400-001	Installation of the Cargo-Compartment Smoke Detectors
ASM 261702
AMM 26-17-15-000-001	Removal of the Lavatory Smoke Detector
AMM 26-17-15-400-001	Installation of the Lavatory Smoke Detector
AMM 31-32-00-860-005	Procedure to Get Access to the SYSTEM REPORT/TEST FIRE PROT Page

3. Fault Confirmation
Subtask 26-17-00-865-054-A ** ON A/C NOT FOR ALL

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

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C NOT FOR ALL
49VU	AIR COND/SDCU/CHAN1	11WQ	C06
122VU	AIR COND/SDCU/CHAN2	12WQ	T18

Subtask 26-17-00-710-064-A ** ON A/C NOT FOR ALL

B. Test
(1) Open the circuit breakers 11WQ and 12WQ.
(a) After 60 seconds, close the circuit breakers 11WQ and 12WQ.
(b) After one more minute, start the subsequent test.
(2) Get access to the MCDU/SDCU menu page AMM 31-32-00-860-005.
(a) Push the line key adjacent to the <ON GROUND FAULTS indication.
(b) The MCDU shows the fault message. If there is no fault, the MCDU shows NO FAILURE.

4. Fault Isolation
Subtask 26-17-00-810-074-A ** ON A/C NOT FOR ALL

A. If the test gives a different maintenance message:

Do the trouble shooting procedure related to the maintenance message.

Subtask 26-17-00-810-075-A ** ON A/C NOT FOR ALL

B. If the test gives the maintenance message TEST OK, no other maintenance action is necessary.

Subtask 26-17-00-810-090-B ** ON A/C NOT FOR ALL

C. If the test gives the status maintenance message SDCU and the maintenance message SDCU/SMOKE DET LOOP:

Refer to the lavatory smoke detection schematic of the Description and Operation chapter AMM 261700 PB 001.
Make sure that the electrical connectors at the SDCU (10WQ) and the related first connected smoke detectors are correctly installed ASM 261702.

(1) If the fault continues:

Read out the TROUBLE SHOOTING DATA (TSD).

The TSD shows the number of smoke detectors (SD) installed on the smoke detection loop, e.g. xxxx xxxx xxxx xxxx A/B. The Customer Layout specifies the number of SD's. If no fault is detected, A is equal to B.

NOTE: A is the number of SD's counted clockwise from the SDCU Channel 1.
B is the number of SD's counted counterclockwise from the SDCU Channel 2.

(a) If the TSD gives the complementary information xxxx xxxx xxxx xxxx 0/B:

Replace the first SD AMM 26-17-15-000-001 AMM 26-17-15-400-001 counted clockwise from SDCU Channel 1.

1 If the fault continues:

Do a check and repair the wiring if necessary between the SDCU (10WQ) and the related first lavatory smoke detector (XWQ):
SDCU (10WQ) connector AA/1A and the first smoke detector (XWQ) connector A/A
SDCU (10WQ) connector AA/1B and the first smoke detector (XWQ) connector A/B ASM 261702.

(b) If the TSD gives the complementary information xxxx xxxx xxxx xxxx A/0:

Replace the first SD AMM 26-16-15-000-001 AMM 26-16-15-400-001 counted counterclockwise from SDCU Channel 2.

1 If the fault continues:

Do a check and repair the wiring if necessary between the SDCU (10WQ) and the related first cargo smoke detector (XWH):
SDCU (10WQ) connector AB/1C and the first smoke detector (XWH) connector A/G
SDCU (10WQ) connector AB/1B and the first smoke detector (XWH) connector A/F ASM 261602.

Subtask 26-17-00-710-065-A ** ON A/C NOT FOR ALL

D. Do the test given in Para. 3.

5. Close-up
Subtask 26-17-00-860-057-A ** ON A/C NOT FOR ALL

A. Put the aircraft back to its initial configuration.

[Rev.8 from Aug 2018] 2026.04.04 04:27:21 UTC