PS Engineering PMA6000M-S - Manual (Page 12)

PS Engineering
PMA6000 Series Audio Selector Panel and Intercom System
Installation Manual
200-066-0006 Page 2-5 Rev. 6, March 2005
NOTICE: To reduce the amount of heat dissipated in the audio selector panel, when used in a 28
Volt aircraft, a 15
Ω, 15 Watt dropping resistor (p/n 701-015-1501) must be installed in series
with the power input.
2.4.6 Existing KMA-24 Installation
If the installation replaces a KMA-24 (series -01, -02 or -03), the existing 44 pin connector can be used for
the bottom connector of the PMA6000 tray as it is, if it is properly installed and wired. A dropping resistor
must be in series with the power in a 28V KMA 24 installation. No other changes are required except for
external marker lights (see Section 3.7.2 for details). The "key" in the existing connector must be located
between pins 7 and 8. This connector will be used in the bottom connector position. (See appropriate Ap-
pendix for complete wiring harness details.)
2.4.7 "Swap" Mode
When a normally-open, momentary, push-button switch is connected between pin 10 on the top connector
and aircraft ground, the user can switch between Com 1 and 2 by depressing this switch without having to
turn the mic selector switch. This yoke mounted switch eliminates the need of removing your hands from
the yoke to change transceivers.
NOTICE: Some older model radios may cause the Swap mode to activate on the release of the
PTT switch, due to the excessive back EMF from the collapsing relay coil field. Verify that back
EMF suppression, in the form of a diode across the T/R relay coil, is present if un-commanded
Swap occurs.
2.4.8 Backlighting
The PMA6000 has an automatic back-lighting system controlled by a photodetector. Additional control can
be gained by the aircraft avionics dimmer control. Connect the dimmer control line to bottom connector pin
D for 14 volt systems, and to bottom connector pin F for 28 volt systems. Pin E is light ground. This instal-
lation provides the ability to bring the back-lighting level to zero. If dimmer control is not used, a constant
low level back light illumination has been established for night-time viewing. The photocell located at the
lower right hand side of the unit face will automatically adjust the backlight of the push-button lamps as
well as the rotary mic selector switch light intensity.
2.4.9 Speaker Loads
Certain VHF Nav/Comms, such as King KX170-series have internal speaker amplifiers. These are not used
with a PMA6000, but must be loaded to prevent unit failure. Connect the speaker output from the
Nav/Com to the appropriate load on the PMA6000 (bottom connector 19 and L for COM 1, etc).
2.4.10 PA Mute
Bottom connector pin 18 is a TTL logic output that is pulled low during PTT operation. This serves as an
input to external public address system to prevent feedback during transmissions.
2.4.11 Middle Marker Sense
The MM Sense output is connected to specific autopilots, and goes high only when a middle marker signal
is received, not in test.
2.4.12 Unswitched Inputs
The PMA6000 has two unswitched inputs. Bottom connector pin 17 is unswitched, but muted by transmis-
sions. This signal can be used for less critical inputs such as airborne telephone ringer.