AUDIO OUTPUT
ENTERTAINMENT
HI PTT-1KEYLINECONTROL SWITCH
BOARDING MUSIC
LO INPUT PTT-2
FWD ATTENDANT PANEL
TAPE REP PWR RLY
PTT-4 PTT-3
AUDIO SELECTOR PANEL
PA AMPLIFIER
PA KEYLINE 28V DC1 AIRPLANES WITH(P11) PASSAUDIO ACCESSORY UNIT
VIDEO ENTERTAINMENT ADRS AMPL CB MUX PWR RLY
Passenger Entertainment System Schematic
Figure 2
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH PASSENGER ENTERTAINMENT ú
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ú ú 03A Page 5 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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MAINTENANCE MANUAL
(1)
The passenger entertainment system is activated by rotating the PES switch to ON. The switch is located on the forward attendant's panel, P21. The PES switch supplies a ground to energize the mux power relay. The contacts in this relay close to supply grounds for the entertainment tape reproducer and main multiplexer. The ground supplied to these units will cause them to power up. The main multiplexer supplies 35v ac power for the SEBs, which in turn supply 5.6v dc for the PCUs.
(2)
Power-up of the entertainment tape reproducer will cause the 1A, 2A and 3A tape transports to enter the play mode. The 1B, 2B and 3B tape transports will rewind to the beginning-of-tape cue point and enter a standby mode. When the end-of-tape cue is detected by an A transport, the corresponding B transport will enter play mode. The A transport will then rewind to the beginning-of-tape cue point and enter a standby mode. The A transport will begin to play when the B transport senses the end-of-tape cue. This process repeats until power is removed or a PA announcement is made.
(3)
If a short power interruption (less than 15 seconds) occurs, the entertainment tape reproducer begins to play at the point of interruption when the power is restored. Power interruptions longer than 15 seconds cause the tape reproducer to initialize upon reapplication of power. In that case, all tape cassettes rewind and cue to their start positions.
(4)
When a PA PTT is initiated, a ground is provided to the entertainment tape reproducer PA keyline causing the tape reproducer to enter a pause mode. Releasing the PA PTT removes the ground, and the tape reproducer restarts at the point of interruption.
(5)
The audio information magnetically encoded on the audio tapes is detected and converted to an electrical waveform by the entertainment tape reproducer heads. The three active heads each supply 4 channels of audio. Twelve audio amplifiers (one for each channel) output the audio signal from the tape reproducer to the main multiplexer.
(6)
The main multiplexer receives the audio channels from the entertainment tape reproducer, and from the PA amplifier. The main multiplexer converts the signals to digital pulses, and combines the information into a single data stream. The data stream goes out to the SEBs.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH PASSENGER ENTERTAINMENT ú
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ú ú 03A Page 6 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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757
MAINTENANCE MANUAL
(7)
When the video tape reproducer plays a tape, the two channels of sound go to the main multiplexer. The VTR sound overrides the two channels of entertainment tape reproducer sound. The VTR sound goes into the data stream sent out to the SEBs.
(8)
The main multiplexer performs the analog-to-digital conversion of the audio waveform by sampling to determine if the wave is rising, falling or constant. For each sample an appropriate digital bit goes into the data stream.
(9)
The data stream is made up of frames of digital pulses. Within each frame is a bit for one sample of each of the 12 audio waveforms. The frame also contains a sync pulse to signal the beginning of a frame, and a command bit with stereo/mono switch information.
(10)
When a PA PTT is initiated, a ground is provided to the main multiplexer PA keyline. The PA announcement audio is converted to digital form and transmitted on all channels.
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