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E 13M69 AUDIO ACCESSORY UNIT (E2-1)
Passenger Address System Schematic
Figure 2 (Sheet 3)

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A 737-300/400/500MAINTENANCE MANUAL

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A 737-300/400/500MAINTENANCE MANUAL
 (2)  
Announcements made from an attendants panel have the second highest priority.

 (3)  
AIRPLANES WITH A WALL MOUNTED TAPE REPRODUCER; The prerecorded announcements have the third highest priority.

 (4)
Boarding music has the lowest priority input.Keying the forward attendant PA microphone mutes the forward attendant speaker(s) and keying the aft attendant PA microphone(s) mutes the aft attendant speakers. This prevents feed-back during attendant announcements.Keying the pilots' PA microphone will disable the muting of both forward and aft attendant speakers.Discrete signals from the passenger signs system cause a low tone chime signal to be sounded. A single low chime occurs whenever the NO SMOKING or the FASTEN SEAT BELT signs are switched on or off.Discrete signals from the attendant call system cause high tone chime signals to be sounded. A single high chime occurs when an attendant call switch is pressed at a passenger service unit (PSU) or from a lavatory.Discrete signals from the cabin interphone system cause high-low chimes to be sounded. A single high-low chime occurs for a crew to attendant call.Voice announcements from the pilots are made through the flight interphone system. The announcements amplified by the PA amplifier are returned to the pilots via the flight interphone system. Amplification by the PA amplifier is enabled by PTT (push-to-talk) inputs.The PA amplifier has circuitry to provide system testing. All PA speakers can be checked. Output level of the amplifier can be determined to allow for adjustments.The system amplifier gain is increased by 6 db to compensate for increased noise levels when either engine is operating.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.AIRPLANES WITH A 346D-2B AMPLIFIER; The self-test switch on the PA amplifier front panel provides tests of the operation status of the PA system. The spring loaded CAL position applies the amplifier output to an internal load. The power applied is displayed on the LED indicators. The TEST position supplies a high chime sound to all speakers. The NORM position is used for system operation. After any tests are done, the switch should always be returned to the NORM position.AIRPLANES WITH A 255-5 AMPLIFIER; Two test switches and a meter are on the front face of the passenger address amplifier. Each switch is spring loaded to the NORM (up) position. The down position is for TEST.

 (1)  
SPKR TEST - When the NORM-SPKR test switch is held in the SPKR TEST position, a calibrated tone is applied to the input of the amplifier and applied to all speakers.

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737-300/400/500MAINTENANCE MANUAL
 (2)  CAL - When the NORM-CAL test switch is held in the CAL position, the output of the passenger address amplifier is disconnected from the speakers and placed across an internal load. A calibrated signal is applied to the amplifier input. A correct MASTER GAIN setting will provide a meter reading of 0 dB on the meter during this CAL test.
 R.  The PA amplifier main output drives all PSU, attendant and lavatory speakers. All main output speakers are connected in parallel. The lavatory speakers are five inches in diameter, each has an input transformer. All PSU speakers are 6.5 inches in diameter and utilize input transformers. The transformer inputs are connected at the COM-2K terminals on all speakers.
　
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