SDCU Single Channel Fault

TASK 26-17-00-810-802-A
SDCU Single Channel Fault

1. Possible Causes

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 261701
ASM 261702
ASM 261703
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
Sequence of Smoke Detectors in Single-Loop Configuration

3. Fault Confirmation
Subtask 26-17-00-865-051-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 26-17-00-710-052-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 26-17-00-810-056-B ** 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 26-17-00-810-091-A ** ON A/C NOT FOR ALL

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

Subtask 26-17-00-810-057-B ** ON A/C NOT FOR ALL

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

Make sure that all electrical connectors are connected to the smoke detectors in the loop.

(1) If the fault continues:

Do a read-out of the TROUBLE SHOOTING DATA (TSD).

NOTE: The TSD read-out shows:

The total number of smoke detectors installed (and found) on the smoke detection loop, e.g. xxxx xxxx xxxx xxx aa/bb.
The cabin layout shows the number of smoke detectors. If no fault is found aa is equal to bb (when aa and bb is the expected number of installed smoke detectors in the loop).
aa is the number of smoke detectors of the SDCU channel 1 (counted clockwise).
bb is the number of smoke detectors of the SDCU channel 2 (counted counterclockwise).

All cargo and lavatory smoke detectors are connected in a single loop, with a specified sequence. The FINs of the lavatory smoke detectors depend on the location of the lavatory in the cabin. You can ignore the FINs of smoke detectors not installed on A/C.

(a) If the TSD gives the value xxxx xxxx xxxx xxx aa/bb (with bb<aa):

Replace the smoke detector(bb) AMM 26-16-15-000-001 AMM 26-16-15-400-001 AMM 26-17-15-000-001 AMM 26-17-15-400-001 counted counterclockwise from the SDCU Channel 2.

1 If the fault continues:

Replace the smoke detector(bb+1) counted counterclockwise from SDCU Channel 2 until the TSD gives the value xxxx xxxx xxxx xxx aa/bb (with aa=bb).

(b) If the TSD gives the value xxxx xxxx xxxx xxx aa/bb (with aa<bb):

Replace the smoke detector(aa) AMM 26-17-15-000-001 AMM 26-17-15-400-001 AMM 26-16-15-000-001 AMM 26-16-15-400-001 counted clockwise from the SDCU Channel 1.

1 If the fault continues:

Replace the smoke detector(aa+1) counted clockwise from SDCU Channel 1 until the TSD gives the value xxxx xxxx xxxx xxx aa/bb (with aa=bb).

(c) If the TSD gives the value xxxx xxxx xxxx xxx aa/bb (with aa=bb, where aa and bb are not the expected number of installed smoke detectors in the loop (smoke detector is like a wire)):
1 Pull the SDCU reset C/Bs 11WQ and 12WQ on the cockpit overhead panels 49VU and 122VU.
2 Disconnect the smoke detector 5WH for A319/320 or 7WH for A321 in the middle of the loop.
3 Push the SDCU reset C/Bs 11WQ and 12WQ on the cockpit overhead panels 49VU and 122VU.
4 Find on which side of the removed smoke detector the number of smoke detectors sensed from the SDCU is less than the number of the smoke detectors installed in the aircraft.
5 Pull the SDCU reset C/Bs 11WQ and 12WQ on the cockpit overhead panels 49VU and 122VU.
6 Install the smoke detector 5WH for A319/320 or 7WH for A321 in the middle of the loop.
7 Disconnect a smoke detector in the middle of the defective side as identified.
8 Push the SDCU reset C/Bs 11WQ and 12WQ on the cockpit overhead panels 49VU and 122VU.
9 Find on which side of the removed smoke detector the number of smoke detectors sensed from the SDCU is less than the number of the smoke detectors installed in the aircraft.
10 Repeat the steps (1)(c)7 to (1)(c)9 until the defective smoke detector is found.
(2) If the fault continues:

Do a check and repair if necessary the wiring between the SDCU and all the connected lavatory and cargo compartment smoke detectors ASM 261602, ASM 261701, ASM 261702 and ASM 261703.

Subtask 26-17-00-710-053-A ** ON A/C NOT FOR ALL

D. Do the test given in Para. 3.

5. Close-up
Subtask 26-17-00-860-051-A ** ON A/C NOT FOR ALL

A. Put the aircraft back to its initial configuration.

[Rev.8 from Aug 2018] 2026.04.04 04:27:20 UTC