Garmin GTN 6 series Maintenance Manual page 70

6.3.3.2.2 Failsafe Operation Check
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. During power-on operation, this
short will not damage the audio panel.
1. Power the GMA 35 off by pulling the audio panel circuit breaker.
2. Check the failsafe operation by exercising the COM1 microphone, microphone key and audio over
the pilot's headphones.
3. Verify that COM1 can key and transmit the pilot's microphone audio by verifying received
sidetone or checking reception of the transmission with another radio tuned to receive this
transmission (verify Pilot PTT and microphone operation is delivered to this transceiver).
4. Turn the unit back on to continue testing.
NOTE
If the configuration setting "COM 1 is connected as COM 2" is set to True, then the
COM 2 microphone should be exercised rather than COM 1.
6.3.3.2.3 COM Transceiver Operational Check
1. Connect a headset to the pilot's headset output and microphone input jack.
2. Verify that each installed transceiver (COM) can be heard when selected.
NOTE
Depending on configuration settings, the mic-selected COM radio may mute audio from
other COM radios.
3. Verify that each installed transceiver keys for transmission and transmits clear audio from the
pilot's mic when selected for transmission and the Pilot PTT key is pressed. Because the audio
panel can be configured to simulate received sidetone internally, verifying transmission with a
separate radio not in the system is recommended.
NOTE
Depending on configuration settings, other transceivers may be muted during transmit.
Also, the audio panel may mute the speaker during PTT.
4. Move the headset to the copilot's headset jacks and verify that any one of the installed transceivers
(testing each is not necessary) receives and transmits copilot mic properly as above.
GTN 6XX/7XX Part 27 AML STC Maintenance Manual
Page 6-6
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190-01007-B1
Rev. 1