Garmin GFC 500 AutoPilot Flashes

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Diane Reim

Filing Flight Plan
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Feb 7, 2023
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Diane Reim
I just upgraded my Glasair III with Garmin avionics - two G5's, 375 gps, and GFC 500 autopilot. Since new, the AP panel lights with flash randomly, making it look like a reboot. It remains engaged, and the flash intervals are random - sometimes 5 seconds apart, sometimes 45 seconds apart. Happen in flight and static on the ground. Avionics shop has replaced nearly everything (thank heavens its still under warranty), including the wiring harness and AP unit, but still has the issue. We have recorded data on SD cards in the G5's, but shows nothing. Garmin customer support is shrugging their shoulders. Anyone else with an issue like this? Any ideas?
 
Sounds like a bad circuit breaker or power supply wires being loose or a short circuit in the wires.
 
MooneyDriver78 said:
Sounds like a bad circuit breaker or power supply wires being loose or a short circuit in the wires.
Click to expand...
Thanks MooneyDriver78. The tech said he hooked it up to an outside power source and ground to rule out bad power supply or interference. Even replaced the entire wiring harness. Really scratching our heads on this one.
 
Is the dimmer for the AP panel internal?

the reason I ask is because I installed an external dimming sensor too close to the instrument itself causing it to freak out. It wasn’t a Garmin AP however. I don’t know dingus about it.
 
Great question...no dimmer that I know of. The avionics shop did the installation and rearranged the components to their standard stack. Thanks Tiimbeck2.
 
Small little voltage drop can cause. We had a garmin gmx200 that was real finicky when there was a voltage drop. Would boot up fuzzy. Or screen upside down sometime.
Does look like it’s rebooting. Light come on same sequence every time?
bench test out of the plane producing same result?
 
Yes, same result when powered and grounded outside the airplane. And no, sequence can be different. Thank you for your insight and experience.
 
Can they (or have they) disconnected all the wiring to the servos, etc, leaving only the unit powered on? That may help isolate the problem to that portion of the wiring.
 
Thanks Skyrys62. Yes, they tried that as well. No change. Just seems strange that it will flash like a reboot but does not disengage.
 
I believe so, but will ask that question again tomorrow when we take the plane in for more work on it. They powered and grounded the AP and controller externally, isolating it from the airplane, and same result. Thanks for the idea.
 
Unless they bench tested it, I would replace the circuit breaker. I had similar issues with my G255, turned out the new CB was defective. Yes the CB tested ok with a meter.
 
Thanks MooneyDriver78. Will ask the shop that question tomorrow too.
 
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