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Garmin GTN-650 Reboots in Flight (long)

Paddy

Well Known Member
My RV-10 has a G3X (non touch) panel with a GTN-650 as the TSO'd navigator for IFR flight, of which I do a lot. The whole shebang has been working great for +400hrs (including 2 Atlantic crossings) without so much as a hiccup. That is until recently when I installed the latest software update for both the G3X (12.20) and the GTN (6.71). All worked fine on a 20min test flight as well as on the first (40min VFR) leg of a long XC about a week later. On the 2nd leg, about 30 min into a 2hr IFR flight, the GTN turned itself off and rebooted. It continued to turn off and reboot like this for the remainder of the flight. Same for the 3rd 2hr leg back home. Put the plane away and went back to the hangar the next day to troubleshoot. Turned on the panel and the GTN boots up, then the screen goes black with a white vertical line down the middle...

A call to Garmin and they say the unit needs to be returned for service. I pony up the $1,500 or so and receive a refurb unit in short order. Slide the new unit in and it comes to life as expected. I check the software version and it's up-to-date with ver 6.71. Expecting my troubles to be over, I head out for a test flight and guess what - it reboots again...

By now I'm thinking I must have an intermittent power supply or ground issue, so I bring up the VPX Pro page on the G3X and wait for it to happen again. There it goes, but there's no fault message on the VPX, no open, no short, no over current - nothing. In fact, the breaker shows a steady 2.9 Amps throughout, even with the screen dark...

Hmm... Time for a deeper dive. I have the GTN wired through a couple of Shottky diodes as part of a dual bus system, so I disconnect the Aux power and connect the GTN power directly to the main avionics power to bypass the diodes altogether. No dice, still shuts off in flight - it's not a bum diode.

Deeper still - I have 2 (electronic) breakers feeding the GTN, one for the COM radio (connector P1003) along with my Audio Panel, and one for the Main board (connector P1001, the VHF NAV board (connector P1004) and my Airinc module, a GAD 29.

I try turning off the breakers in flight - the COM breaker kills the Audio Panel and delivers the appropriate warning on the GTN that the radio is inop, although the screen is still up and the rest of it seems to be working normally.

Pulling the NAV breaker turns the GTN off completely as expected, since the main board is turned off when pins 19 and 20 are depowered in connector P1001. I'm starting to run out of ideas for an easy fix, so I bust out the multimeter and tear into the panel looking for a bad crimp, loose connector or some other builder induced failure (I built the panel...).

I'm in deep now, screens out, avionics racks out, connectors disassembled and every one of those pesky high density pins Ohmed out, wiggled, pulled and thoroughly checked out. Nothing... I put it all back together.

Getting just a little defeated by now... One last feeble idea before I go back to Garmin and plead for help... I hook up the audio panel to the same breaker as the Main GTN board in the hopes that if there is an intermittent power interruption, maybe I'll hear a click in the system to give me a clue.

Last test flight and I wait for the inevitable reboot. The GTN turns off after 20min or so and reboots. Not a click, a flicker or a peep from anything else in the panel. The Audio Panel seems to be doing just fine. I'm exhausted.

Call up Garmin on Tues morning and talk to a member of Team X. I get a couple of sentences out and he stops me, says he's heard of something like this and will get with one of the engineers and call me back. Cool, maybe I'm gonna get this fixed! No call by 4pm, so I call again and get the same guy that helped me with the exchange unit a few weeks earlier. He seems genuinely interested in helping and says he's never heard of anything like this. I go through all my troubleshooting and ask if it could possibly be software related, since it has happened on 2 units now with ver 6.71. He says there are so many units in operation with the new software and nobody else has had a problem. Nevertheless, he takes my info again and promises a follow-up email to gather more info for the engineers. Saturday now and nothing in my inbox.

Any ideas from the collective on this one?
 
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Temporarily wire an *single* inline fused power wire to the unit. Bypass all the magic stuff and power off the main bus. Go fly. I know a guy (or two) that had issues like this with his VPX.

Does your engine monitor track voltage? Can you dump the data and graph it on Savvy looking for voltage glitches?
 
Paddy - it’s worth checking the VPX wig/wig menu to make sure the GPS is not ‘ticked’ in the menu. Don’t ask how I know about this, & it only happened once🙄
 
Had a similar issue a while back and Garmin suggested I roll back to the previous software first and see if it does it. Mine did not do it again. I downloaded the newest software again and did a reinstall and never had a problem since.
 
Thanks for the responses

Thanks for the responses,
Blaplante,
There are seven powered pins divided up among 3 separate connectors on the GTN, so a single wire test isn't practical, however I do agree that bypassing the VPX seems like good test logic and I'll give it a try. Flight data, including system voltage is captured on an SD card with the G3X, but I didn't see anything in there. I think the maximum sample rate may be too slow to catch a transient that's fast enough not to flicker any lights on the audio panel that's on the same circuit.

JakeJ
Just checked the VPX setup and the only wig-wag is on the lights. Good one there tho - hadn't thought of that!

Nova RV
Thanks for the info - was your issue the same with the GTN? I am becoming more convinced that it's a software issue - either with the G3X or the GTN, both of which I updated at the same time. I also changed a serial data setting on the GTN to get the fuel data to push over from the G3X, per the Garmin instructions.
 
Are you sure the radio is fully inserted in the rack, I can't tell you how many times I've seen similar issues when the radio was not fully seated in the rack (and check that the connectors and screws that attach the back plate are all secure).
 
Thanks for the responses,
Blaplante,
There are seven powered pins divided up among 3 separate connectors on the GTN, so a single wire test isn't practical, however I do agree that bypassing the VPX seems like good test logic and I'll give it a try. Flight data, including system voltage is captured on an SD card with the G3X, but I didn't see anything in there. I think the maximum sample rate may be too slow to catch a transient that's fast enough not to flicker any lights on the audio panel that's on the same circuit.

JakeJ
Just checked the VPX setup and the only wig-wag is on the lights. Good one there tho - hadn't thought of that!

Nova RV
Thanks for the info - was your issue the same with the GTN? I am becoming more convinced that it's a software issue - either with the G3X or the GTN, both of which I updated at the same time. I also changed a serial data setting on the GTN to get the fuel data to push over from the G3X, per the Garmin instructions.

Yes, my software issue was with the GTN update, apparently the 1st update I did was somehow corrupted. The fact that you had 2 units do the same thing though is very odd, but it can't hurt to roll back or even just reinstall the update to rule that out.
 
fan?

Is there a chance the cooling fan has died? Maybe it is overheating? Should be easy enough to check.

Jay
 
Are you sure the radio is fully inserted in the rack, I can't tell you how many times I've seen similar issues when the radio was not fully seated in the rack (and check that the connectors and screws that attach the back plate are all secure).

I was going to suggest something along a similar thought process.

Have you checked for continuity in all the power pins in the harness connector? As well as the point you split the line coming from the VPX into the multiple feeds?

The fact that this is happening on two different units may imply the issue is local to your aircraft. Perhaps vibrations are causing an intermittent wiring issue? One of the wires that is about to break or a pin that isn’t making consistent contact? I’ve also seen pins that weren’t pushed in all the way, but look ok upon visual inspection. But when the connector is mated the pin is pushed back into the dsub and doesn’t make good contact. I’ve had experience with these scenarios previously and it’s a PITA trying to troubleshoot those high density dsubs. If one of those lines goes open, there may not be enough current to power the unit.

Good luck!
 
1 wire ... RFI

When I said power it with one wire, what I meant was "single source". Yes you need to then power all the requisite pins on the unit, but I wanted all that to come from one place (and not the VPX), not some from circuit A, some from circuit B...

Some more things to look at and check - could be an RFI issue. Does it reboot shortly after you transmit on the radio? If not, can you fly somewhere that doesn't require a transponder and try a flight with the transponder off?

I had a COM radio that was locking up... replaced it and got rid of the problem but later found I had a bad connection in the main battery wire to the breaker bus bar. Strongly suspect the radio was fine! Had been wondering why my indicated voltage was a bit less than I'd expect...
 
I have had a similar issue with v12.2 software, only it’s with the SL30. It locks up after 20 minutes of flight and only in flight. I turned off the serial port to the sl30 and problem disappears. I rolled the sw back to 12.0 and problem gone. Try rolling the sw back to 12.0. 12.2 has issues. Garmin claims they can’t repeat the problem. There are so many variables with installations in terms of com ports and general configuration that they may never find it.
 
Had a reboot on my G3X 650 after 30 mins of flight last week with the latest software update. Landed 10 minutes later. Planning to fly this week to see if it repeats
 
It certainly smells like a s/w issue. Given the timing of the updates and failure, s/w is where I would be spending my time. Coincidence is real, but often a head fake. This is especially true if the problem appeared on the first or second flight after the update. The consistent 30 minute timing also suspicious and points to s/w.

I would roll back the GTN software and test. Then roll back the G3X software and test. There is a good amount of data flowing from the G3X to the GTN and it is possible that a mal-formed data packet or other transmission anomaly could cause the GTN to reboot. Testing of these occurrences is VERY hard for the s/w engineers and a lot of possible errors end up un-tested or even un-accounted for in the code, as they can't imagine all of the possible error modes that could occur out in the wild. If the s/w gets something that makes it think something bad has happened and no error code was written, it can default back to a sub-routine that forces a reboot. This is often the final line of error handling, intended as a fail safe when corruption is expected.

Larry
 
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