Master Warning Lights

 (1)  
AIRPLANES WITHOUT RESETTABLE OVERSPEED SIREN AURAL WARNING; The red master WARNING lights are located on both ends of the pilots' glare shield P7. The lights come on when the Master Warning module in the Warning Electronics Unit generates a warning signal. Pressing the indicator light cap will turn off the light.

 (2)  
AIRPLANES WITH RESETTABLE OVERSPEED SIREN AURAL WARNING (POST-SB 31-68 OR PRR 54813); The red master WARNING lights are located on both ends of the pilots' glare shield P7. The lights come on when the Master Warning module in the Warning Electronics Unit generates a warning signal. Pressing the indicator light cap will turn off the light and the siren overspeed warning.

Discrete Warning Light

 (1)  
The red CONFIG discrete warning light is located on the center instrument panel. The light comes on when the Configuration Warning module in the Warning Electronics Unit generates a warning signal. The light is powered by the master dim and test circuit (AMM 33-16-00).

Loudspeakers

 (1)  
The aural warning loudspeakers are located above the captain's and first officer's seats. Each loudspeaker is a permanent magnet speaker driven by an internal single stage amplifier. The two speakers provide aural tones and messages when turned on by either the left or right Siren/Owl Aural Warning module. The aural warning loudspeaker amplifiers are powered from the 28 volt dc standby bus.

Aural Reset Switch

 (1)  
The aural reset switch generates a ground signal to the Aural

 Warning module to stop the fire bell sounds.Speed Brake Handle Position Switch

 (1)  
The speed brake handle position switch is located inside the P10 panel. The switch is a thru-contact microswitch with a roller control arm. If the switch is set at the down detent position, a ground is applied to the configuration warning module. This activates a warning during takeoff.

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A

757
MAINTENANCE MANUAL

 3. Operation
_________
 A. Functional Description
 (1)  Warning System Interfaces (Fig. 2)
 (a)  
The Warning Electronics Unit (WEU) power supply modules receive 115 volts ac from the WARN ELEX A and B circuit breakers. The warning speakers receive 28 volts dc from the AURAL WARN circuit breakers. The master WARNING lights receive 28 volts dc from the master dim and test circuits (AMM 33-16-00).

 (b)  
The WEU receives digital input signals from four sources. These include the Radio Altimeter, Ground Proximity warning computer, Air Data computer, and the Autopilot systems on the ARINC 429 digital bus. It also receives analog status discrete signals from many airplane systems. These signals are processed by different modules in the WEU under microprocessor control to provide the warning signals.
　
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