PS Engineering
PMA7000BT Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-780-0204
Page 2-6
Rev. 1, July 2015
2.5.8
Backlighting
The PMA7000BT has an automatic dimming of the pushbutton green annunciator LEDs and marker lamps
controlled by a photocell. Control of the unit backlighting (white LEDS) is through the aircraft avionics
dimmer. Connect the dimmer control line to J1 pin D for 14 volt systems, and to J1 pin F for 28 volt sys-
tems. Pin E is light ground.
If an external dimmer control is not used, a constant low level back light illumination can be established for
nighttime viewing. Pin D or F (depending on system voltage) must be tied to power (J1, pin 20) for the
back lighting system to work. The photocell mounted in the unit face will automatically adjust the intensity
of the push-button green annunciator LEDs.
2.5.9
Unswitched inputs
J1, pins T, 17, U and X are unswitched, unmuted inputs. These inputs are presented to the pilot and copilot
regardless of the audio configuration, and will always mute the entertainment inputs. These 510
Ω inputs
can be used for altimeter DH audio, GPS waypoint audio, autopilot disconnect tones, or any other critical
audio signal. J1
Pin T is provided to the pilot’s headset even when the unit is off, or in fail
-safe mode.
If the KMA 24 installation include
s “External Speaker” or “Internal Speaker” connections to J1 Pins X and
U respectively), these will have to be disconnected to avoid interference with the Unswitched inputs #3 and
#4.
NOTE: Inputs 1, 2 and 4 are fixed (1:1), and any audio level adjustments must be made at the input source.
Input 3 (Bottom Connector pin U) has adjustable attenuation.
2.5.10 PA Mute (J1, Pin 18)
Pin 18 of J1 is a TTL logic output that is pulled low during PTT operation. This serves as an input to exter-
nal public address system to prevent feedback during transmissions.
2.5.11 Public Address Function (J2, Pin 18)
By connecting the top connector (J2), Pin 18 to ground, the pilot’s microphone audio is placed on the cabin
speaker output. When the pilot’s PTT is activated, his voice is heard ove
r the speaker. The copilot can con-
tinue to use the selected com.
We recommend installing a toggle switch to connect the cabin speaker output (pin W, bottom connector) to
a rear or public address speaker instead of the cockpit speaker close to the pilot. This will prevent feedback.
2.5.12
Control Output (J2, Pin A)
Pin A of the top connector is pulled to ground whenever the AUX button is depressed. This serves as a con-
trol line for external devices, such as an entertainment system that the pilot wishes to control.
This could be used in conjunction with a PA to control J2, Pin 18, as well as an external relay to change to
the cabin speaker from the cockpit.
This pin can also be used to control passenger Karaoke Mode, by connecting to pin V of the J2.
This pin can also be used to control Alternate Intercom Mode (2.4.15.1), by connecting J1 pin 14 to J2 pin
A.
2.5.13 Intercom wiring
The top connector (J2) is for the intercom and additional functions. See Appendix for intercom connection
configurations. It is critical to the proper operation of this system to have this connector wiring made in
accordance with these diagrams. Use 2- and 3-conductor, MIL-spec cable as shown. Connect the shields at
the audio panel end only, and tie to the audio low inputs as shown.
NOTE: The top connector harness can be custom made by PS Engineering, Inc. Simply call the factory and
obtain a wire harness work-sheet. The harness will be made to your specifications and fully functionally
tested. All hardware is included.