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ACP Components
The ACP has these components:
* Power supply
* Front panel lights and switches
* Switching multiplexer
* Volume control multiplexer
* Select circuits
* Emergency circuit.
Power Supply
The ACP gets 15v dc from the REU. The ACP converts this
voltage to 12v dc and 5v dc which gives power for electronic
circuits.
Master dim and test (MD&T) sends 28v dc or 16v dc to the
microphone selector lamps. The airplane electrical system
sends 5v ac for panel lighting.
Front Panel Lights and Switches
The ACP has these front panel components:
* Microphone select switches with mic select lights
* Filter switches
* Receiver select switches and volume controls.
The mic select lights get 28v dc or 16v dc from the MD&T
circuits. A mic select light turns on when it gets a ground from
the electrical interlock programmed logic array (PLA) circuit.
When you push the microphone select switch, it sends 5v dc to
the PLA. The PLA is an electrical interlock circuit. It makes a 4
bit binary code for the selected switch.
System selection is latched into the PLA. The PLA sends the
applicable code to the switching multiplexer. The PLA also
sends a signal to turn on a receiver volume control when you
push the microphone select switch.
Push the receiver volume control to hear audio from the related
system. The receiver volume control switch sends a dc voltage
from a potentiometer (0 to 12v dc) to the multiplexer. The
multiplexer sends this voltage to the REU to set the radio output
volume level. When the audio volume control switch is off, 12v
dc goes to the REU and you cannot hear the system audio.
Switching Multiplexer
The switching multiplexer gets these signals:
* Microphone select binary code from the PLA circuit
* DC voltages from filter switches
FLIGHT INTERPHONE SYSTEM - AUDIO CONTROL PANEL FUNCTIONAL DESCRIPTION
EFFECTIVITY
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* DC voltages from the service interphone, PA, and speaker
volume controls.
The switching multiplexer sequentially selects the inputs. The
data output goes to the REU as a control system data word. This
multiplexer operation stops when the volume control
multiplexer operates.
Volume Control Multiplexer
The volume control multiplexer gets DC voltages from the
remaining receiver volume controls.
The volume control multiplexer sequentially selects the inputs.
The data output goes to the REU as a control system data word.
This multiplexer operation stops when the switching multiplexer
operates.
Select Circuits
A multiplexer selects each input in sequence for a given time. A
clock in the REU increases the value of a counter. This counter
provides the select address for the two analog multiplexers.
Two multiplexers combine the data from all the switches and
the controls. The scan inhibit circuits prevent the operation of
one multiplexer output while the other scans.
Emergency Circuits
The REU gives power for the ACP. You lose ACP power when
for these conditions:
* REU has no power
* ACP has the ALT selection.
These conditions occur when you lose power in the ACP:
* The ALT/NORM relay has no power
* The data line to the REU identifies MASK/BOOM selection
* 28 volts from MD&T goes through the ALT/NORM relay
contacts to the VHF 1 mic selector switch lamp for the captain
and observer, and VHF 2 mic selector switch lamp for the
first officer.
FLIGHT INTERPHONE SYSTEM - AUDIO CONTROL PANEL FUNCTIONAL DESCRIPTION
EFFECTIVITY
SHZ ALL 23-51-00
Page 44
D633A101-SHZ1 Feb 10/2005
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
23-51-00-013
FLIGHT INTERPHONE SYSTEM - AUDIO CONTROL PANEL FUNCTIONAL DESCRIPTION
FLIGHT INTERPHONE SYSTEM - AUDIO CONTROL PANEL FUNCTIONAL DESCRIPTION
EFFECTIVITY
SHZ ALL 23-51-00
Page 45
D633A101-SHZ1 Feb 10/2005
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
23-51-00-013
General
These components send a push-to-talk (PTT) signal to the
remote electronics unit (REU):
* Audio control panel (ACP) radio-intercom PTT switches
* Control wheel PTT switches
* Hand microphone PTT switches.
Set the radio-intercom PTT switch on the ACP to R/T to send a
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