SDCU can no longer control the Smoke-Detection Loop

TASK 26-16-00-810-819-A
SDCU can no longer control the Smoke-Detection Loop

1. Possible Causes

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
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
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 26-16-00-865-065-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 26-16-00-710-087-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 26-16-00-810-101-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 26-16-00-810-102-A ** ON A/C NOT FOR ALL

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

Subtask 26-16-00-810-103-A ** ON A/C NOT FOR ALL

C. If the test gives the maintenance message TEST NOT POSSIBLE SELECT TROUBLE SHOOTING DATA:

make sure that all electrical connectors are connected to the smoke detectors in loop A and loop B.

(1) If the fault continues:

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

The TSD shows the total number of smoke detectors installed on the smoke detection loop, e.g. xxxx xxxx xxxx xxxx aa/bb (aa=bb shows all installed smoke detectors). The cabin layout specifies the number of smoke detectors.

NOTE: aa is the number of smoke detectors counted clockwise from the SDCU Channel 1.
bb is the number of smoke detectors counted counterclockwise from the SDCU Channel 2.

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

Sequence of Smoke Detectors in Single-Loop Configuration (A319/320)

----------- Lavatory Location Designation

!SDCU ! A C B T W H K D E F G

!CHANNEL1 !--1WQ--3WQ--2WQ--20WQ--23WQ--8WQ--9WQ--4WQ--5WQ--6WQ--7WQ--!

! ! !

!CHANNEL2 !--1WH--2WH--3WH--4WH--5WH--6WH-----------------------------!

! !

-----------

Sequence of Smoke Detectors in Single-Loop Configuration (A321)

----------- Lavatory Location Designation

!SDCU ! A C B H K S T L M D E

!CHANNEL1 !--1WQ--3WQ--2WQ--8WQ--9WQ--19WQ--20WQ--14WQ--15WQ--4WQ--5WQ----!

! ! !

! ! G F !

!CHANNEL2 !--1WH--2WH--3WH--4WH--5WH--6WH--7WH--8WH--9WH--10WH--7WQ--6WQ--!

! !

-----------

If the number of detected smoke detectors is not the same as the number of pin-programmed smoke detectors (for example aa < number of pp, bb < number of pp, aa+bb <> number of pp), one smoke detector as a minimum on the loop is in a specific failure mode that prevents the correct operation of all in the loop.

NOTE: It can help you to disconnect/open the loop in the middle and thus to decrease the number of possible locations of the defective smoke detector. The total number of smoke detectors installed on the disconnected smoke detection loop is shown. If the number is less than the number of pin-programmed smoke detectors, the defective smoke detector must be in the related part of the loop.

(a) Open the SDCU circuit breakers 11WQ and 12WQ.
(b) Disconnect the cargo smoke detector 5WH for A319/320 or 7WH for A321.
(c) Do a read-out of the TSD and compare the number of detected smoke detectors to the number of pin-programmed smoke detectors:

for A319/320, SDCU channel 2 must detect bb=04 smoke detectors if 5WH was disconnected.
for A321, SDCU channel 2 must detect bb=06 smoke detectors if 7WH was disconnected.

(d) If there is a discrepancy, replace the smoke detector one after the other from the related SDCU channel until the TSD gives the total number of smoke detector installed on the SDCU channel:

for cargo smoke detector (WH) AMM 26-16-15-000-001 AMM 26-16-15-400-001.
for lavatory smoke detector (WQ) AMM 26-17-15-000-001 AMM 26-17-15-400-001.

(e) Reconnect the smoke detector 5WH for A319/320 or 7WH for A321.
(f) Close the SDCU circuit breakers 11WQ and 12WQ again. Make sure that there is an interval of approximately 80 seconds (SDCU power-up is 20 sec. and SD initialization is 60 sec.) before you continue.

Subtask 26-16-00-710-088-A ** ON A/C NOT FOR ALL

D. Do the test given in Para. 3.

5. Close-up
Subtask 26-16-00-860-068-A ** ON A/C NOT FOR ALL

A. Put the aircraft back to its initial configuration.

[Rev.8 from Aug 2018] 2026.04.04 04:27:19 UTC