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MASTER WARNING AND CAUTION LIGHTS - TROUBLE SHOOTING
1.  General
A.  Trouble shooting the master caution lights and system master caution annunciators is best done in conjunction with use of the master dim and test switch. Inoperative light bulbs can be quickly located when the LIGHTS switch is positioned to TEST. If a specific section of system master caution annunciator is inoperative, the trouble can usually be traced back to the corresponding P5 module. Refer to the Wiring Diagram Manual for specific circuit details. If a specific system indicator light is inoperative but tests OK with the master dim and test switch, refer to the associated system trouble shooting procedures. Certain system indicators may always be illuminated whenever the airplane is on the ground (such as door open indicators); this is normal. The following charts indicate possible light failures, probable cause and corrective action. See par. 2 for the master caution trouble shooting chart. See par. 3 for the master dim and test trouble shooting chart. The charts assume the airplane is on the ground with power applied to all systems.
B.  All trouble shooting procedures are based on the assumption that wiring is OK and that electrical power is available. If the corrective action in the procedure does not correct the problem, check wiring using the wiring diagram.
NOTE:  When replacing component perform electrical check for proper operation before closing assembly.
2.  Master Caution Trouble Shooting Chart
TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
Master caution lights and annunciators do not illuminate for any system fault indication  Open transitor-diode dimming circuit in M469 annunciation and dimming module  Press system master caution annunciator. If master caution lights do not illuminate while annunciator is pressed, M469 module is faulty  Replace M469 annunciation and dimming module 
Master caution lights and annunciators do not illuminate for systems on any one P5 (or P8-1) module   System module logic circuit inoperative  Refer to specific system and simulate a failure for module more than one system indicator light on module. If master caution lights and annunciators fail to illuminate, system module  Replace system module 

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TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
System indicator light does not illuminate or is dim when LIGHTS switch held to TEST Group of lights do not illuminate when LIGHTS switch held to TEST Unable to dim all lights All lights do not illuminate when LIGHTS switch held to TEST Group of lights go off when LIGHTS switch positioned to DIM  Burned out bulb Master test relay contact open or one dim relay has contacts open Master dim diode is open LIGHTS switch S270 inoperative Open zener diode  Hold LIGHTS switch to TEST. Observe system indicator light illuminates. If not, bulb is faulty Hold LIGHTS switch to TEST. Observe group of lights do not illuminate Master test relay R33 or a dim relay is probably faulty Conduct continuity check through each relay to isolate faulty relay (Refer to Wiring Diagram Manual for specific circuits) Perform master caution lights power sources test (AMM  33-15-0/501) Hold LIGHTS switch to TEST. If lights do not illuminate, switch is faulty Position LIGHTS switch to DIM. Observe which lights go off. Check continuity of zener diodes M207, M208, M209, M210 and M394 in load control center P6 to isolate faulty zener diode. (Refer to Wiring Diagram Manual to check lights on specific zener diode circuit)  Relamp system indicator light Replace master test relay R33. Replace master dim module M564. Replace master dim relay R34. Replace auxiliary master dim relay R87 Replace master dim module M564 Replace either M207, M208, M209, M210 or M394 

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TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
One of the following system indicator lights inoperative  Open transistor-diode dimming circuit in M469 annunciator and dimming  Relamp system indicator light. Hold LIGHTS switch to TEST. If light is still inoperative, annunciation and dimming module is faulty  Replace M469 annunciation and dimming module. 
　
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