26-11-00
 ALL  ú ú 02 Page 8 ú Oct 25/84
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 ENGINE FIRE DETECTION SYSTEM - TROUBLE SHOOTING
_______________________________________________
 1.  General_______
 A.  Fire detection system trouble usually is indicated by false alarm, or absence of fire warning lights and alarm bell or overheat lights when TEST switch is actuated.
 (1)  If a short circuit has occurred, the associated detector inoperative light on fire detection accessory unit M279 will illuminate. If an open circuit has occurred, the associated warning lights will not illuminate and both detector inoperative lights will illuminate during FIRE/OVHT test.
 B.  Check associated lights before trouble shooting.
 (1)  
Lights on fire control panel P8, MASTER CAUTION lights and FIRE WARN lights on panel P7 are checked by using lights master test circuit (Ref 33-15-00 A/T).

 (2)  
Detector inoperative lights on M279 are checked by pressing lights.

 C.  False alarms (engine overheat or fire warnings) are usually intermittent and rarely persist for any length of time. Intermittent false warnings can occur whenever the system is subjected to vibration; i.e. engines running, in flight, taxiing, etc. If a false alarm should persist, isolation of the individual sensor, connector or interconnecting wiring will be required. Isolation of the faulty component can be accomplished with the help of the trouble shooting charts.
 D.  AIRPLANES WITH CONNECTORS; the detector and interconnecting wiring can be checked with an ohmmeter. An open detector can be found by making a continuity check between center pins or sockets on connectors on the ends of the elements. Shorts can be found by testing for continuity between the pins or sockets and the shell of the connector. If moisture in a connector is cause of false alarm, remove moisture by blowing dry nitrogen on the connectors.
 E.  AIRPLANES WITH TERMINAL LUGS; the detector and interconnecting wiring can be checked with an ohmmeter. An open detector can be found by making a continuity check between center pins, sockets or terminal lugs on connectors at the ends of the elements. Shorts can be found by testing for continuity between the pins, sockets or terminal lugs and the shell of the connector. If moisture in a connector is the cause of a false alarm, remove moisture by blowing dry nitrogen on the connectors.
 F.  Test fire control panel P8 after installation (Ref 26-11-00 A/T).
 2.  Prepare for Trouble Shooting____________________________
 A.  Check that the following circuit breakers are closed:
 (1)  
FIRE PROTECTION DETECTION ENG NO. 1 on panel P6

 (2)  
FIRE PROTECTION DETECTION ENG NO. 2 on panel P6

 (3)  
FIRE PROTECTION DETECTION - APU on panel P6

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 26-11-00
 ALL  ú ú 02 Page 101 ú Jul 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 (4)  
MASTER WARN & CONT on panel P6

 (5)  
CONTROL CABIN LIGHTING INDICATOR MASTER DIM BUS (nine circuit breakers) on panel P6-3

 B. Open the following circuit breakers:
 (1)  
FIRE PROTECTION DETECTION APU on panel P6

 (2)  
OVHT WHL WELL WING BDY on panel P6

 C. Provide electrical power (Ref 24-22-00/201).
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 26-11-00
 ALL  ú ú 02 Page 102 ú Oct 25/84
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL

Engine Fire Detection Troubleshooting Charts
　
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