E. The rotary mike selector switch enables crewmembers to select any one of seven communication facilities. The mike selector switch can direct the crewmember's microphone output and control circuits to the VHF transmitters, HF transmitters, the two interphone systems and, when pulled out of detent position, to the PA system. The mike selector switch also directs VHF and HF receiver audio, and audio from the service, flight or PA system amplifiers to the isolation amplifier input. The audio common lines, which are terminated on electronic rack shelf E2-1, are also completed through the mike selector switch. The mike selector switch also completes power for the appropriate green indicating lights when VHF, HF, flight interphone, or PA is selected. The isolation amplifier output is connected to the volume control. The volume control adjusts the audio signals to the headphones and, on the captain's and first officer's audio selector panels, the associated loudspeaker. A filter circuit ensures that voltage transients do not damage the transistorized amplifier. Audio outputs from the captain's, first officer's and observer's panels are also connected to the voice recorder system (Ref 23-71-0).
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AUDIO SELECTING SYSTEM - TROUBLE SHOOTING
1. General
A. An inoperative audio selector panel can usually be detected if audio or keying circuits are incomplete on more than one select system. Replacement of the panel will usually correct the problem. If difficulty is experienced in monitoring a particular system, isolation of the panel can be accomplished by first comparing reception with another audio selector panel. If audio signals are not available at any of the audio selector panels, then probably the monitored system is inoperative. Refer to Chapter 34 for those systems not covered in Chapter 23.
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AUDIO SELECTING SYSTEM -ADJUSTMENT/TEST
1. Test Audio Selecting System
A. General
(1) The audio selector panels are tested as part of the individual communication and navigation systems tests. Refer to Chapter 34 for those systems not covered in Chapter 23.
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AUDIO SELECTING SYSTEM - DESCRIPTION AND OPERATION
EFFECTIVITY
UC ALL EXCEPT CC-CIM WA N236WA thru N239WA and N4571M GJ B2509 and B2510
1. General
A. The audio selector panels enable the control cabin crewmembers to transmit or receive on the radio communication systems, communicate using the flight and service interphone systems, or make announcements over the PA system (if installed). Airplane VHF navigation, DME, marker beacon, and ADF receivers may also be monitored.
B. Audio selector panels are located on the control stand at the captain's and first officer's stations. The observer's audio selector panel is located on overhead panel P5.
C. The flight interphone system headphones, handheld mikes, boom mikes and oxygen mask mikes are connected through jacks to the audio selector panels at each crewmember's station. All audio selector panel functions are connected in parallel by the paralleling network on shelf 1 of electronics rack E2.
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