RESET
UNTIL M/W RESETAPU FIRE
NEXT
FWD CARGO FIRE

WARNING
LANDING CONFIGINPUT
WARNINGAFT CARGO FIRE U PROCRESET
ARINC
FIRE/OVHT LOGIC >400
429
TEST  L RA BUS #2
FT
RCVR
MASTER
DET INTERNALS
DC DR
SOFTWARE DIM & TEST SAME ASEA
STDL RADIO ALTIMETER HARDWARE
CAPT MASTERWARN & CAUTION
RESET B
CABIN P
MASTER LIGHTS
HIGH L & R
PRESSURE
DIM & TEST PS RESET
RESET A
10,000 FT
SIREN/OWL HIGH ALT
CABIN ALTITUDE L/R EICAS
1
SEL SW
WARNING SW
COMPUTER POWER
A & B
F/O MASTER WARN &SUPPLY
CAUTION LIGHT/SW+5V DC
-12V DC
CABIN P
1 GUN 004-007,206
PRESSURE +12V DC
14,680 FT
CABIN HIGH ALTITUDEMASTER WARNING
1
WARNING SW
Master Warning Module Schematic
Figure 4

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757
MAINTENANCE MANUAL

 (4)  Bell/Chime Aural Warning Module Function (Fig. 5)
 (a)  
The Bell/Chime Aural Warning module generates the signals to drive the firebells and the communication system chimes. The module receives +5 volts dc and |12 volts dc generated by the power supply modules.

 (b)  
Fire bell function

 1)  The fire bell logic circuit receives five analog discrete fire warning signals from the fire detector control panel. These signals are the left and right Engine, the Auxiliary Power Unit, and the forward and aft Cargo compartment Fire signals. The analog discrete inputs provide a logic 0 signal to the inverting input buffer circuits.
 2)  The buffer circuit digital output is sent to the microprocessor that controls the firebell sequence. The processed signal is routed to the firebell aural generator through the takeoff inhibit logic. If there is no inhibit signal, the warning is routed through to the preamplifier and out to the loudspeakers.
 3)  The preamplifier gain control provides either high or low volume for the aural signal. A high gain will occur if one or more of these conditions are true: a) Landing gear is down and locked. b) Airplane is on the ground. c) T/O inhibit mode is activated. d) Altitude is less than 32,000 feet and MACH number is
 greater than 0.6.
 4)  The firebell warning is inhibited during takeoff. The inhibit is initiated when a logic 0 signal from the No. 2 AIR/GND relay is applied to the interface buffer circuit. The buffer circuit output is fed to the microprocessor. It processes the signal through the inhibit override logic to generate a logic 1 takeoff inhibit signal. It also starts the 20-second delay timer.
 5)  After 20 seconds or after 400 feet of radio altitude is reached, the microprocessor generates a logic 0. This signal is applied to the inhibit logic to cancel the inhibit functions.
　
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