Garmin GTN 6 series Maintenance Manual - page 70

GTN 6XX/7XX Part 27 AML STC Maintenance Manual

190-01007-B1

Page 6-6

Rev. 1

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.