33-15-00
 ALL  ú ú 01 Page 4 ú Mar 15/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 4.  Annunciation and Dimming Module
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 A.  The annunciation and dimming module consists of three printed circuit cards, a transistor circuit and diodes mounted within a box. Two electrical connectors are on the side of the box and a mounting plate is on the front. The module is installed with screws on the left side of the P9 control stand panel. Card A3 contains diodes which isolate individual system control of the system master caution annunciators from the master caution lights and provide diodes for various systems indicator light circuits. Cards A1 and A2 contain transistor circuits with zener diodes which cause certain system indicator lights to dim when the master dim and test switch is operated. A separate transistor circuit and zener diode is connected to the master caution lights and causes the master caution lights and system master caution annunciator to dim.
 5.  Master Dim Module
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 A.  The master dim module consists of a printed circuit card with a relay, diodes and a transistor circuit. The card is installed in a card rack in P6 load control center. The relay connects zener diodes and resistors in the light dimming circuits to the P5-4 ac systems generator and APU module and to the P5-10 air conditioning module. The diodes provide isolation between dual power sources for the master dim and test circuits. The transistor circuit is not used.
 6.  Operation
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 A.  Master Caution Lights
 (1)  The master caution lights inform the pilots that a system fault indicator light has illuminated on a pilot's instrument panel. The system master caution annunciator informs the pilots which system has a fault. Pressing either the pilot's or copilot's master caution light extinguishes the master caution lights and the system master caution annunciators; however, the system faulty indicator light on the instrument panel remains illuminated until the fault is corrected. The pilots may recall faulted system indications on the system master caution annunciators by resetting either annunciator. All annunciator lights will illuminate while the annunciator is pressed. When released, only those systems with illuminated fault indicators will cause the corresponding system master caution annunciator to remain illuminated.
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 33-15-00
 ALL  ú ú 01 Page 5 ú Nov 15/93
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 (2)  The P5 overhead panel modules with the system indicator lights and the P8-1 fire protection module are connected to the master caution. Each module is also connected to one of the system master annunciators. The master caution triggering and reset circuits are part of each system module . Two types of system indicator lights are used on the modules; a ground seeking type and a power seeking type. In a typical ground seeking indicator light circuit, when a system fault is detected, a ground is applied to illuminate the system indicator light and the master caution lights. Power for the fault light is either from a system circuit breaker or from a DIM & TEST circuit breaker. A fault causes the input to G1 to go low. G1 output then goes high, causing a pulser to trigger the SCR and bias transistor S1 on. A ground is then completed to turn on the system master caution annunciator and master caution light. Momentarily pressing the master caution light removes power from the SCR causing it to go off to extinguish the master caution lights and annunciators. Resetting the system master caution annunciator completes a ground to G1 causing the pulser to operate again and retrigger the SCR. The SCR again turns on the system master caution annunciator if the system fault is not corrected and the system indicator light remains illuminated.
 B. Master Dim and Test
 (1)  
The system annunciator lights in the control cabin are dimmed or tested with the LIGHTS switch. The switch is spring loaded from the TEST position to BRT position . Holding the switch to the TEST position applies a ground to master test relay R33. The master test relay then applies either a ground or DIM & TEST 28 volts dc to the system indicator lights . The lights then illuminate until the LIGHTS switch is released.

 (2)  
Power for system annunciator lights is from circuit breakers on 28v dc bus-1, 28v dc bus-2 and the 28v dc battery bus . A diode network in master dim module M564 provides a dual power circuit to each distribution line. Zener diodes are used for decreasing the voltage and dimming system lights. Secondary circuit breakers distribute power for the majority of the system lights. Refer to the Wiring Diagram Manual for specific circuit details. Some lights use system power for their operation, in which case either a transistor and zener diode circuit in annunciation and dimming module M469, is used to dim the light, or a ground and zener diode is applied directly to the light by master dim relay R34 or the dim relay in the master dim module. Auxiliary master dim relay R87 applies either DIM & TEST 28 volts dc or a ground for operation of the transistor and zener diode dimming circuits in the annunciation and dimming module. The dim relays are energized when the LIGHTS switch is positioned to DIM. Master dim relay R34 and the dim relay in the master dim module then insert zener diodes into the lights circuits to dim the lights. Auxiliary master dim relay R87 either removes a ground or applies power in each light circuit.
　
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