(c)
The self-test switch on the PA amplifier front panel provides tests of the operational status of the PA system. The momentary AMP TEST position applies the PA amplifier main output to an internal load. The power applied across the load is displayed on the LED indicators. The SPKR TEST position causes a calibrated high chime tone from the main and auxillary outputs to all speakers. The NORM position is used for system operation. After performing any tests, the switch should always be returned to the NORM position.
AIRPLANES WITH COLLINS AMPLIFIERS; Passenger Address Audio
(a)
Each audio input into the PA amplifier has a PTT control signal. Priorities within the PA amplifier are in numerical order with No. 1 as the highest priority input.
(b)
Compression and amplification circuits within the PA amplifier have internal and external adjustments. The MASTER GAIN on the front panel allows the amplifier to be calibrated for full power output to a particular speaker load. The PA amplifier is capable of providing up to 120 watts from the main output and up to 20 watts from the auxillary output.
(c)
The PA amplifier has circuitry to provide system testing. All PA speakers can be checked. Loads on the amplifier output circuit can be measured. Output levels of the amplifier can be measured to allow for adjustments.
Speaker Distribution
(a)
The PA amplifier main output drives all speakers. All speakers are connected in parallel. Speakers installed near attendant station handsets have a muting relay which disconnects the speakers when the handset is taken off hook. Reference wiring diagram (WDM 23-31-42) for speaker location, equipment numbers and connector numbers.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
23-31-00
ALL ú ú 11 Page 8 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
(5)
Video System Control Unit (AMM/23-32-00)
(a) The video system control unit (AMM 23-32-00) can route the VTR sound through the PA system speakers. The VTR sound goes through the video control relay, to the priority 3 (PTT-3) input of the PA amplifier.
(6)
Tape Reproducer (Fig. 3)
(a)
On/off and volume control of the tape reproducer is provided by the MUSIC control on the forward attendant panel P21. Rotating the MUSIC control clockwise from the OFF position supplies a ground to the tape reproducer remote on/off control pin causing the tape reproducer to energize. The MUSIC control switch also provides a ground to the PTT-4 (priority 4) input of the PA amp.
(b)
Audio from the tape reproducer is provided to the PA amplifier. The PA amplifier will output the tape reproducer audio provided a higher priority input (pilot or attendant announcement) is not present.
B. AIRPLANES WITH PED PA AMPLIFIERS; BITE
(1)
PA Amplifier Front Panel
(a)
The SPKR TEST/NORM/AMP TEST self-test switch, the OVERLOAD light and the -2 to +2 dB output lights enable proper operation of the PA system to be checked.
(b)
The -2 to +2 dB display indicates the PA amplifier test output power relative to 70.7 vrms. The OVERLOAD light comes on whenever the PA amplifier is current limiting because of an excessive load.
(2)
PA Amplifier Test
(a) Holding the test switch to the momentary AMP TEST position provides an internal test of the PA amplifier. 1) The main and auxillary outputs are disabled from the
speakers. 2) All gain circuits are overridden and PTT inputs are
disabled. 3) A calibrated internal input tests the main amplifier. 4) A O dB | 1 dB light indicates a satisfactory PA amplifier
test.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
23-31-00
ALL ú ú 09 Page 9 ú Sep 28/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
PASSENGER ADDRESS AMPL
Boarding Music Schematic
Figure 3
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. GUN 001-007 ú 中國航空網 www.k6050.com 航空翻譯 www.aviation.cn 本文鏈接地址：757 AMM 飛機維護手冊 COMMUNICATIONS 通訊(39)
