757 AMM 飞机维护手册 仪表 CHAPTER 31 - INSTRUMENTS 2(95)

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 7)  A fire bell self test is initiated by pressing the ENG/APU/CARGO switch on the FIRE/OVHT TEST panel on the pilots' aft control stand. The bell rings when the test switch is pressed.
 (c)  Chime Function
 1)  There are three analog discrete input signals that turn on the chime function on the aural warning module. These inputs provide logic 0 to the interface inverting buffer circuits. The discrete signals are generated when any of the following operations occur: a) The Audio Accessory Unit sends a signal to the aural
 warning module, when it receives an input from an attendant call to the flight compartment. b) A Crew Call is made from the P62 control panel in the nose Wheel Well. c) A Selcal signal is generated from the Selcal decoder, when installed.
 2)  The inverting buffer output signals enable the logic circuits which control the chime generator. The chime output is routed through the preamplifiers to the loudspeakers to provide the chime sound. The chime sound lasts for .9 second.
 (5)  Siren/Owl Aural Warning Module (Fig. 6)
 (a)  Two Siren/Owl Aural Warning modules are installed. The operation of the modules are identical and paralleled. The left module drives the left aural warning loudspeaker. The right module drives the right aural warning loudspeaker.
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 (b) Siren Function 1) There are five analog discrete input signals that enable the siren function on the aural warning module. These are overspeed, autopilot disconnect, cabin altitude, and takeoff and landing configuration warning signal discretes. The overspeed discrete is supplied from the left or right air data computer. Autopilot disconnect No. 1 and No. 2 signals are supplied from the left, center, and right flight control computers. Takeoff and landing warnings are supplied from the configuration warning modules. The analog discretes provide a logic 0 to the module interface buffer circuit. 2) The inverting buffer output signals enable two sets of logic circuits. These circuits control two identical siren aural generators. The output signals are then routed through preamplifiers to the loudspeakers to give the siren sound. The siren sounds continuously until the warning condition is corrected or manually cancelled for the Landing warning.
 3)  The Landing configuration warning aural can be cancelled by pressing the GND PROX/CONFIG GEAR OVRD switch. This provides a logic 0 signal to the inverting input buffer circuit. The inverter buffer output signal controls the Landing Warning cancel circuit.
 (c) Owl Caution Aural (Level B) Function 1) There are two analog discrete input signals from other systems that enable the owl caution aural. These signals provide a logic 0 to the interface inverter buffer circuits. The discrete input signals are the following: a) Altitude alert signals from the WEU altitude alert module b) Level B cautions generated from the EICAS computer
　
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