190-01878-02
GMA 342/345 Installation Manual
Rev. 5
Page 3-4
3.7 Post Installation Checkout
CAUTION
Check wiring connections for errors before inserting the GMA 342/345 into the rack.
Incorrect wiring could cause internal component damage.
An in-aircraft checkout may be performed in the aircraft on the ramp with known good microphone,
headset, and avionics receivers.
3.7.1 Failsafe Operation Check
1. Remove power to the unit by pulling the GMA 342/345 breaker.
2. Connect a mono headset to the pilot’s headset output jack and pilot’s mic jack.
NOTE
Use of a true mono headset is required for this test to ensure proper wiring even if a stereo
jack is provided in the installation. Wiring left channel (tip contact) and right channel
(ring contact) backwards will cause failsafe mode not to function with mono headsets.
Use of a true mono headset is required for this test (not a stereo headset with a mono/
stereo switch because headset manufactures differ on how they accomplish this switching).
This will guarantee the condition of the right channel (ring terminal) being shorted to the
return (sleeve terminal) by the mono headset’s plug. This short occurs because of the
physical design of the headset plug contacts and is an inevitable consequence of plugging
a mono headset into a stereo jack. During power-on operation, this short will not damage
the audio panel.
3. Verify that COM1 transceiver can be heard in the pilot’s headset.
4. Verify that COM1 can key and transmit the pilot’s mic audio by verifying received sidetone or
checking reception of the transmission with another radio tuned to receive this transmission (verify
Pilot PTT and mic operation is delivered to this transceiver).
5. Apply unit power by restoring the audio breaker to the normal operating position
3.7.2 Transceiver Operational Check
1. Perform a ramp test radio check by exercising the installed transceivers, microphone, microphone
key, and audio over the headphone.
2. Verify that communications are loud and clear and PTT operation is correct.
3.7.3 Aircraft Receivers Check
1. Select the audio source corresponding to each installed avionics unit and check for audio over the
headsets.
2. Verify each installed unswitched (alert) source can be heard when the source is instructed to play a
simulated alert/message.
NOTE
For the GMA 342 and 345 (2-COM version) unit AUX inputs, pressing the AUX1 button
selects/deselects the AUX 1 and the AUX 3 receiver. Pressing the AUX2 button selects/
deselects the AUX 2 receiver.
NOTE
For the GMA 345 3-COM unit, a single AUX button is used to select all 3 AUX inputs for
simultaneous monitoring.
