NOTE: Since the speakers are tested when power is first
____ applied to the MAWEA, a false fail indication will be generated if speaker power is not on. Be sure that the AURAL WARNING L SPEAKER and AURAL WARNING R SPEAKER circuit breakers are on before applying power to the MAWEA.
 1)  If an internal fault is detected, the red CARD FAULT LED will turn on.
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 (c)
(d)

(e)

(f)

(g)

(h)

(i)

(j)

A
747-400 MAINTENANCE MANUAL
 2) If an input fault is detected, the yellow INTERFACE FAULT LED will turn on. 3) If both an internal and an input fault is detected, then
 only the red CARD FAULT LED turns on.The aural synthesizer cards receive discretes from the master monitor cards when a warning is issued. Depending on the level of warning being issued the aural synthesizer logic will generate:
 LEVEL_____ WARNING
 A . . . . SIREN OR BELL

 B . . . . OWL SOUND

A chime is used for flight crew awareness. Voice audio is generated by the ground proximity warning computer. Each is amplified and routed to the aural warning speakers. The master warning lights will illuminate and a message will be shown on the main EICAS display indicating the warning.Normally, the left aural synthesizer card drives the captain's aural warning speaker while the right aural synthesizer card drives the first officer's aural warning speaker.Level B aurals, except altitude alert, are activated via the EIU.The aural synthesizer cards continuously monitor each other. In the event of a software failure in one card the remaining card will drive both aural warning speakers.Each aural synthesizer card produces a fail indicator output pulse every 100 ms. Each card continuously monitors the other card's pulses.In the event of a failure of one card, the pulses from that card will stop. Thus, the other card is able to detect the failure.When a software failure in one of the aural synthesizer cards occurs, the microprocessor in the failed card senses that condition and: 1) Produces a discrete that illuminates the red LED on the
 front of the failed card
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747-400 MAINTENANCE MANUAL
 2) Stops generating the FAIL INDICATOR OUTPUT pulse
 (k)  
The absence of the FAIL INDICATOR OUTPUT pulse causes the microprocessor in the operational aural synthesizer card to disable the inhibit logic. This allows aural signals out of the operational aural synthesizer card to the output amplifier of the failed one.

 (l)  
As long as the output amplifier of the failed aural synthesizer card is still functional, the left aural warning speaker will still operate.

 (11)
 Configuration Warning Card

 (a)  The configuration warning card performs these functions: 1) Takeoff warning alert 2) Landing warning alert 3) Speedbrake alert 4) Stabilizer green band indication 5) Glide slope antenna switching

 (12)
 Airplane Tail Identification Card

 (a)  
The airplane tail identification card monitors coded information from nine character buttons. These nine characters consist of any combination of alpha, numeric, "-", ".", or blank characters.

 (b)  
These character buttons identify the airplane identification code and are mounted on the MAWEA monitor panel. Each character button consists of seven interface pins. By grounding different combinations of these pins through a ground line within the button itself, the desired characters are selected.

 (c)  
The combinations selected on each button are sensed by the discrete input interface in the airplane tail identification card. The information is supplied to an analog to digital converter. The airplane identification code information is sent to the EIUs by an ARINC 429 transmitter.

 (13)
 Signal Collection Cards

 (a)  Each signal collection card monitors the status of 64 discrete inputs from various systems and sensors. Each card can receive a maximum of two ARINC 429 inputs.
　
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