PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010
Page 2-11
Rev. 29, Sept. 2021
2.4.7
"Swap" Mode
When a momentary, normally open, push-button switch is connected between pin U (14 V) or 18 (28V
lighting) on the unit connector and aircraft ground, the user can switch from Com 1 to 2 to 3 etc. by de-
pressing this switch without having to change the mic selection. This yoke-mounted switch eliminates the
need to remove your hands from the controls to change transceivers.
NOTE: Swap mode is active if the proper DIP switch selection is made internally to the unit.
2.4.8
Backlighting
The PAC24 has an automatic dimming of the pushbutton annunciator LEDs and marker lamps controlled
by a photocell. Control of the unit backlighting is through the aircraft avionics dimmer. Connect the dim-
mer control line to J3 pin 18 for 14-volt systems, and to J3 pin U for 28-volt systems. Pin 17 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 18 or U (depending on system voltage) must be tied to power (J3, pin 25) for the
back lighting system to work. The photocell mounted in the unit face will automatically adjust the intensity
of the push-button annunciator LEDs.
2.4.9
Unswitched inputs
J3, pin 10 is the unswitched input number 1 and J3 pin 14 is unswitched input 2. These inputs are presented
to the pilot and copilot regardless of the audio configuration, and will always mute the entertainment in-
puts. These 510Ω inputs can be used for altimeter DH audio, GPS waypoint audio, autopilot disconnect
tones, or any other critical audio signal.
NOTE: In installations where an expansion unit is NOT used, the passenger and copilot audio output is
paralleled (J1, pin b). Therefore, unswitched audio will
be heard by the passenger(s).
Use an expansion
unit, P/N 11606, or 11606R (remote) to isolate passenger audio from unswitched alert audio.
2.4.10 PA Mute (J3, Pin 8)
Pin 18 of J3 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.
2.4.11 Public Address (J3, Pin B)
When the Speaker mode switch is in the PA mode, and the pilot’s PTT is activated, his voice is heard over
the PA speaker output on J3, Pin B. The copilot can continue to use the selected com.
In a dual installation, both the pilot and copilot panels can be connected to separate PA Speakers, for in-
stance, one ramp hailer, and one public address speaker.
NOTE: Connecting two audio panels to a single speaker for cockpit and/or cabin address
can result in damage to the audio panel.
2.4.12 Intercom wiring
See Appendices 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.
2.4.12.1 Push to talk intercom
The PAC24 can be used as an IntelliVox® intercom, or, as a keyed intercom. Switching J3 pin W to
ground will inhibit the IntelliVox® and the intercom squelch will not open until the ICS PTT switch is ac-
tivated.
The following pins are used to control the intercom when PTT ICS is desired. Pin 11 must be grounded
through a momentary switch for the pilot to talk on the intercom (with W also grounded). Pin M must be
grounded through a momentary switch for the copilot to talk on the intercom (with W also grounded).