PAS -AIRPLANE SYSTEMS AND CSMU INTERFACES
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PAS -PRERECORDED ANNOUNCEMENT MACHINE
Purpose
The prerecorded announcement machine (PRAM) sends recorded announcements and boarding music to the passenger address/cabin interphone (PA/CI) controller.
General
The PRAM is a solid state device. It keeps the announcements in memory devices as digital voice data.
The PRAM keeps as many as 500 announcements.
The PRAM keeps the announcements and music on three memory cards; one for message data and two for music data. Each card has a 40 megabyte capacity.
The PRAM has a card slot for downloading data into the PRAM.
The PRAM has a maintenace port jack for shop use only.
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777 AIRCRAFT MAINTENANCE MANUAL
PAS -PRERECORDED ANNOUNCEMENT MACHINE
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PAS -SPEAKER DRIVE MODULE
Purpose
The speaker drive modules (SDMs) send passenger address (PA) audio to the PA speakers. They also send inputs from ambient noise sensors (ANSs) to the PA/CI controller.
Physical Description
An SDM is about six inches wide and seven inches long. It weighs about one and a half pounds.
Functional Description
The SDMs get digital audio from the PA/CI controller and change it to analog audio. Each SDM can control as many as four speakers independently.
The SDMs also have a chime generator to make chime sounds.
Some SDMs connect to an ANS. The SDM supplies power to the ANS. The ANS sends a signal proportional to the cabin noise level. The SDM digitizes the signal and sends it to the PA/CI controller.
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777 AIRCRAFT MAINTENANCE MANUAL
PAS -SPEAKER DRIVE MODULE
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PAS -AMBIENT NOISE SENSOR
Purpose
The ambient noise sensors (ANSs) measure cabin noise levels. The passenger address system uses ANS data to automatically adjust the PA volume.
Physical Description
The ANS is about four inches wide and five inches long. It weighs about 1/3 pound.
Functional Description
The ANS has a microphone that monitors cabin sounds. It makes a dc signal in proportion to the cabin noise level. The ANS sends the signal to the nearest speaker drive module.
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777 AIRCRAFT MAINTENANCE MANUAL
PAS -AMBIENT NOISE SENSOR
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PAS -SPEAKERS
Purpose
The speakers produce the passenger address audio in the passenger cabin.
Locations
Most speakers are in the ceiling panels over the passenger seats and aisles. There are also speakers in the galleys, above the doors, and in each lavatory.
Functional Description
The speakers get audio signals from the speaker drive modules (SDMs). They change the electrical signal into an acoustic signal.
Training Information Point
A dot on one speaker terminal identifies it as positive. Connect the red lead to the positive terminal.
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777 AIRCRAFT MAINTENANCE MANUAL
PAS -SPEAKERS
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PAS -SDM, ANS, AND SPEAKER INSTALLATION
SDM Installation
The speaker drive modules (SDMs) are above the cabin ceiling panels on the left side of the stow bin support assembly. Four screws attach the SDM to the support assembly.
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