DOC AIRBUS | TSM A320FSDCU Double Channel Fault
TASK 26-17-00-810-803-A
SDCU Double Channel Fault
1. Possible Causes
A. Referenced Information
3. Fault Confirmation
Subtask 26-17-00-865-052-A ** ON A/C NOT FOR ALL
Subtask 26-17-00-810-058-B ** ON A/C NOT FOR ALL
Subtask 26-17-00-860-052-A ** ON A/C NOT FOR ALL
[Rev.8 from Aug 2018]
2026.04.04 04:27:20 UTC
SDCU Double Channel Fault
1. Possible Causes
- wiring
A. Referenced Information
| REFERENCE | DESIGNATION |
|---|---|
| TSM TASK 26-17-00-810-806-A | Pin Programming Configuration Fault |
| 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 ConfigurationSubtask 26-17-00-865-052-A ** ON A/C NOT FOR ALL
A. Table of the circuit breakers used in this procedure:
Subtask 26-17-00-710-054-A ** ON A/C NOT FOR ALL | PANEL | DESIGNATION | FIN | LOCATION |
|---|---|---|---|
| ** ON A/C NOT FOR ALL | |||
| 49VU | AIR COND/SDCU/CHAN1 | 11WQ | C06 |
| 122VU | AIR COND/SDCU/CHAN2 | 12WQ | T18 |
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.
(3) If the MCDU shows the fault message, open the circuit breakers 11WQ and 12WQ.
(a) After 20 minutes, close the circuit breakers 11WQ and 12WQ.
(b) After one more minute, start the subsequent test.
(4) 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(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.
(3) If the MCDU shows the fault message, open the circuit breakers 11WQ and 12WQ.
(a) After 20 minutes, close the circuit breakers 11WQ and 12WQ.
(b) After one more minute, start the subsequent test.
(4) 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.
Subtask 26-17-00-810-058-B ** ON A/C NOT FOR ALL
A. If the test gives a different maintenance message:
Subtask 26-17-00-810-093-A ** ON A/C NOT FOR ALL - Do the trouble shooting procedure related to the maintenance message.
B. If the test gives the maintenance message TEST OK, no other maintenance action is necessary.
Subtask 26-17-00-810-059-B ** ON A/C NOT FOR ALL C. If the test gives the maintenance status message SMOKE DET FAULT and the trouble shooting data gives the complementary information SMOKE DET LOOP:
Make sure that all electrical connectors are connected to the smoke detectors in loop A and loop B.
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+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 no value for xxxx xxxx xxxx xxx aa/bb:
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 (2)(d)7 to (2)(d)9 until the defective smoke detector is found.
(3) If the fault continues:
Subtask 26-17-00-810-101-B ** ON A/C NOT FOR ALL Make sure that all electrical connectors are connected to the smoke detectors in loop A and loop B.
NOTE: This paragraph 4.C.(1) to (4) is only applicable to ionization type smoke detectors P/N PAI2800-xx, GAI2800-xx and PAI2830-xx.
NOTE: If ionization type smoke detectors and photo-electric type smoke detectors are installed on the same aircraft, the trouble shooting procedure must be done for photo-electric type smoke detectors first. It is necessary to start the procedure at an smoke detectors location adjacent to a photo-electric type smoke detector, and to do the measurements in the direction of the photo-electric type smoke detector (see paragraph 4.D.(4)). The trouble shooting procedure must be done as given. If all photo-electric type smoke detectors are serviceable, it is necessary to do the trouble shooting procedure for the ionization type smoke detectors.
(1) If the fault continues:- Do a check of the SDCU PIN PROGRAMMING (Ref. TSM TASK 26-17-00-810-806).
- Do a read-out of the TROUBLESHOOTING DATA (TSD).
NOTE: The TSD read-out shows:
(a) If the TSD gives the value xxxx xxxx xxxx xxx aa/bb (with bb<aa): - 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).
- 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.
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.
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 no value for xxxx xxxx xxxx xxx aa/bb:
- Replace the lavatory smoke detectors AMM 26-17-15-000-001 and AMM 26-17-15-400-001 in sequence (start from the first LAV smoke detector of SDCU CHANNEL 1, usually LAV A).
- Replace the cargo smoke detectors AMM 26-16-15-000-001 and AMM 26-16-15-400-001 in sequence (start from the first cargo smoke detector of SDCU CHANNEL 1).
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 (2)(d)7 to (2)(d)9 until the defective smoke detector is found.
(3) 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.
- Do a check and repair the related wiring which is shown in the WIRING REPORT ASM 261602, ASM 261701, ASM 261702 and ASM 261703.
D. If the test gives the maintenance message SMOKE DET LOOP:
(a) Do the troubleshooting procedure for the photo-electric-type smoke detectors first.
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+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 (2)(c)7 to (2)(c)9 until the defective smoke detector is found.
(3) If the fault continues:
(b) Disconnect the cargo smoke detector 5WH for A319/320 or 7WH for A321.
(c) Connect the red lead of the DC meter to the pin G and the black lead to the pin F at the aircraft-side connector of the detector.
(d) Close the SDCU circuit breakers 11WQ and 12WQ for 40 to 60 seconds.
(e) The DC meter pulses between DC voltages.
1 If the highest voltage peak shown on the voltmeter is less than 22VDC,
(h) During the subsequent 40 to 60 seconds, do a check of the voltage with the voltage-meter. The DC meter pulses between DC voltages.
1 If the highest voltage peak shown on the voltmeter is less than 22VDC,
(j) Connect smoke detector 5WH for A319/A320 (or 7WH for A321) to the loop again.
(k) If step (e) 1 applies, do a test for each smoke detector in the sequence of channel 2, that is between SDCU channel 2 and 5WH for A319/320, between SDCU channel 2 and 7WH for A321.
3 Measure the voltage (DC mode) between pin F and pin G of the aircraft-side connector.
a If the highest voltage peak shown on the voltmeter is less than 22VDC, the smoke detector in the location (n-1) is defective. Replace the smoke detector.
b If the highest voltage peak shown on the voltmeter is equal to 24+/-2V (voltage level pulses between 0V and 24V), the smoke detector on the location (n-1) is serviceable.
4 Open the SDCU circuit breaker 11WQ and 12WQ.
5 Connect the n-th smoke detector to the loop again and disconnect the smoke detector on the location (n+1).
6 Do the steps (k) 1 to step (k) 5 for each smoke detector that is in a subsequent position in the loop to examine each smoke detector.
3 Measure the voltage (DC mode) between pin A and pin B of the aircraft-side connector.
a If the highest voltage peak shown on the voltmeter is less than 22 VDC, the smoke detector on the location (n-1) apparently is defective. Replace the smoke detector.
b If the highest voltage peak shown on the voltmeter is equal to 24+/-2VDC (voltage level pulses between 0VDC and 24VDC), the smoke detector on the location (n-1) is serviceable.
4 Open the SDCU circuit breakers 11WQ and 12WQ.
5 Connect the n-th smoke detector to the loop again and disconnect smoke detector on location (n+1).
6 Do the steps (l) 1 to step (l) 5 for each smoke detector that follows to examine each smoke detector.
(n) Do a check of the "ON GROUND FAULTS" indication.
(5) If the fault continues:
Subtask 26-17-00-710-055-A ** ON A/C NOT FOR ALL - Make sure that all electrical connectors are connected to the smoke detectors in the loop.
NOTE: This paragraph 4.D. (1) to (6) is only applicable to photo-electric type smoke detectors P/N PPA1100-xx, PPA1101-xx, PPA1102-xx, PPA1103-xx, PPA1200-xx, PPA1201-xx, PPA1202-xx, PPA1203-xx, PPA1204-xx, PAPE2800-xx, GPA1202-xx and GPA1203-xx.
(1) If the aircraft has ionization-type smoke detectors and photo-electric-type smoke detectors: (a) Do the troubleshooting procedure for the photo-electric-type smoke detectors first.
- Start the procedure at a smoke-detector adjacent to a photo-electric-type smoke detector.
- Measure in the direction of the photo-electric-type smoke detector (refer to Para. 4.D. (4) of this subtask).
- Do the troubleshooting procedure as shown, ignore the ionization-type smoke detectors.
- Do the trouble shooting procedure for the ionization-type smoke detectors.
- Do a read-out of the TROUBLESHOOTING DATA (TSD).
NOTE: The TSD read-out shows:
(a) If the TSD gives the value xxxx xxxx xxxx xxx aa/bb (with bb<aa) - 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).
- 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.
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.
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 (2)(c)7 to (2)(c)9 until the defective smoke detector is found.
(3) If the fault continues:
- Do a check of the SDCU PIN PROGRAMMING (Ref. TSM TASK 26-17-00-810-806).
- Do this procedure for the identification of a defective photo-electric type smoke detector.
NOTE: For this procedure two persons are necessary, one in the cockpit and one to move from detector to detector.
One digital multimeter that can measure 24VDC, with a CAPTURE MAX/MIN function, is necessary.
The sequence of the troubleshooting procedure (step (a) to step (n)) is mandatory. Do not stop if you find one defective smoke detector at the start of the troubleshooting procedure. One or more smoke detector(s) that follow(s) can have a defect.
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. The sequence of the connection and disconnection process shown in the diagram is mandatory.
(a) Open the SDCU circuit breakers 11WQ and 12WQ. One digital multimeter that can measure 24VDC, with a CAPTURE MAX/MIN function, is necessary.
The sequence of the troubleshooting procedure (step (a) to step (n)) is mandatory. Do not stop if you find one defective smoke detector at the start of the troubleshooting procedure. One or more smoke detector(s) that follow(s) can have a defect.
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. The sequence of the connection and disconnection process shown in the diagram is mandatory.
(b) Disconnect the cargo smoke detector 5WH for A319/320 or 7WH for A321.
(c) Connect the red lead of the DC meter to the pin G and the black lead to the pin F at the aircraft-side connector of the detector.
(d) Close the SDCU circuit breakers 11WQ and 12WQ for 40 to 60 seconds.
(e) The DC meter pulses between DC voltages.
1 If the highest voltage peak shown on the voltmeter is less than 22VDC,
- For A319/320: One or more smoke detector(s) of 1WH, 2WH, 3WH, 4WH is(are) defective (between SDCU channel 2 and 5WH).
- For A321: One or more smoke detector(s) of 1WH, 2WH, 3WH, 4WH, 5WH, 6WH is(are) defective (between SDCU channel 2 and 7WH).
- For A319/320: The smoke detectors between the SCDU and 5WH (channel 2) are serviceable.
- For A321: The smoke detectors between the SDCU and 7WH (channel 2) are serviceable.
NOTE: If the measurements of step (e) are done after short intervals, it is not necessary to do step (f). If not, it is necessary to do the step (d) again.
(g) Connect the red lead of the DC meter to the pin A and the black lead to the pin B of the aircraft-side connector of the detector. (h) During the subsequent 40 to 60 seconds, do a check of the voltage with the voltage-meter. The DC meter pulses between DC voltages.
1 If the highest voltage peak shown on the voltmeter is less than 22VDC,
- For A319/320: One or more of the smoke detector(s) between SDCU channel 1 and 5WH is(are) defective.
- For A321: One or more of the smoke detector(s) between the SDCU channel 1 and 7WH is(are) defective.
- For A319/320: The smoke detectors between SDCU channel 1 and 5WH are serviceable. Smoke detector 5WH apparently is defective. Replace the smoke detector.
- For A321: The smoke detectors between SDCU channel 1 and 7WH are serviceable. Smoke detector 7WH apparently is defective. Replace the smoke detector.
(j) Connect smoke detector 5WH for A319/A320 (or 7WH for A321) to the loop again.
(k) If step (e) 1 applies, do a test for each smoke detector in the sequence of channel 2, that is between SDCU channel 2 and 5WH for A319/320, between SDCU channel 2 and 7WH for A321.
NOTE: The test for the last smoke detector is completed when the smoke detector 5WH for A319/A320 or 7WH for A321 was disconnected and connected to the loop again.
1 Disconnect the n-th smoke detector of channel 2. NOTE: "n" gives the position of the smoke detector in the loop. At the start of this procedure, "n" refers to the second cargo smoke detector n=2. Cargo smoke detector 2WH (n=2) is disconnected to examine the detector 1WH (n-1) before it in the loop (adjacent to 2WH).
2 Close the SDCU circuit breakers 11WQ and 12WQ and stop 40 to 60 seconds. 3 Measure the voltage (DC mode) between pin F and pin G of the aircraft-side connector.
a If the highest voltage peak shown on the voltmeter is less than 22VDC, the smoke detector in the location (n-1) is defective. Replace the smoke detector.
b If the highest voltage peak shown on the voltmeter is equal to 24+/-2V (voltage level pulses between 0V and 24V), the smoke detector on the location (n-1) is serviceable.
4 Open the SDCU circuit breaker 11WQ and 12WQ.
5 Connect the n-th smoke detector to the loop again and disconnect the smoke detector on the location (n+1).
6 Do the steps (k) 1 to step (k) 5 for each smoke detector that is in a subsequent position in the loop to examine each smoke detector.
NOTE: An incorrect voltage measured at the location number n shows a defective smoke detector on the location (n-1).
(l) If step (h) 1 applies, do a test for each smoke detector in the sequence of channel 1. That is between SDCU channel 1 and 5WH for A319/320, between SDCU channel 1 and 7WH for A321. NOTE: The test for the last smoke detector is completed when smoke detector 5WH for A319/320 or 7WH for A321 was disconnected and connected to the loop again.
1 Disconnect the n-th smoke detector of channel 1. NOTE: "n" gives the position of the smoke detector in the loop. At the start of this procedure, n refers to the second lavatory smoke detector n=2. If there are three lavatories in the cabin, on the locations A, D and E: The second lavatory smoke detector 4WQ (n=2) is disconnected to examine the detector 1WQ (n-1) in the loop before 4WQ.
2 Close the SDCU circuit breakers 11WQ and 12WQ and stop 40 to 60 seconds. 3 Measure the voltage (DC mode) between pin A and pin B of the aircraft-side connector.
a If the highest voltage peak shown on the voltmeter is less than 22 VDC, the smoke detector on the location (n-1) apparently is defective. Replace the smoke detector.
b If the highest voltage peak shown on the voltmeter is equal to 24+/-2VDC (voltage level pulses between 0VDC and 24VDC), the smoke detector on the location (n-1) is serviceable.
4 Open the SDCU circuit breakers 11WQ and 12WQ.
5 Connect the n-th smoke detector to the loop again and disconnect smoke detector on location (n+1).
6 Do the steps (l) 1 to step (l) 5 for each smoke detector that follows to examine each smoke detector.
NOTE: An incorrect voltage measured at the location number n shows that the smoke detector on the location (n-1) is defective.
(m) Close the SDCU circuit breakers 11WQ and 12WQ again and stop for approximately 80 seconds (SDCU power-up is 20 sec. and SD initialization is 60 sec.). (n) Do a check of the "ON GROUND FAULTS" indication.
(5) 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.
- Do a check and repair the related wiring which is shown in the WIRING REPORT ASM 261602, ASM 261701, ASM 261702 and ASM 261703.
E. Do the test given in the Para. 3.
5. Close-upSubtask 26-17-00-860-052-A ** ON A/C NOT FOR ALL
A. Put the aircraft back to its initial configuration.