GTN-650 problem

Hey Guys,

I am having a really funny thing happen to my GTN-650. Not sure if others have seen it. For a while now that the weather is getting warmer on taxi out to the runway I would always loose GPS for about 30 seconds. Didn't think much about it, but one day I was taxiing without my headset on.

The GTN Fan Kicked on and boom, lost GPS. So it has been happening with the warmer temps, when the fan kicks on I loose GPS for a short time.

This seems really scary to me for a TSO'd IFR GPS, any thoughts on this problem? Has this happened to others?

Thx

I have noticed the fan kicking on a lot more lately, but I have yet to see it take out the GPS signal.

Never noticed any issues with the fan and GPS signal.

I would check your antenna, antenna connections, antenna location etc.

I've had the same issue twice inflight, in an R44 helicopter. Didn't think of heat, but that could well explain it.

I believe there have been other conversations about the antenna getting hot and loosing reception. Funny that it happens for you at the same time as the fan.

I wonder if the motor on the fan is creating interference with the GPS signal. How far is the antenna from the fan? Turning on the AFS 4500 near our 696 reduces signal strength in half. It does not take much EMI to disrupt a GPS signal.

George

In addition to the antenna placement, do you have the specified antenna cable length, and is it coiled up under the boot cowl?

As a point of reference, my antenna is on my canopy, right at my shoulder. The cable snakes around a little bit in an attempt to use up the excess length, but it isn't coiled on itself anywhere.

My antenna is firewall forward under the cowl on a shelf next to my Dynon antenna. The Dynon GPS has never lost a signal, but the Garmin occasionally loses lock and takes a minute or two to re acquire. I never considered temperature as a cause. Is there something in writing from Garmin on this topic??

The TSO requires something like a 60 inch minimum (don't quote me) antenna lead, AND a 3 sq ft ground plane. I just ran across the ground plane requirement in the installation manual the other night. With so many roll bar and engine mounted GPS antenna's (no ground plane), I had not considered this before.

Don't know if this is a factor or not, but it may drive me to move my antenna if I ever get serious about IFR flying.

No problem with mine, yet.

Good morning everyone,
my apologies for the delay in looking at this and responding as I've been out on business travel the last couple of weeks. The GTN units are tested per all TSO standards with a temp limit of -20 degrees C. to 55 degrees C, or -4 degrees F to 131 degrees F. The fan actually has two modes of operation with a low and high setting it is designed to kick on when the internal main board area gets to a temp of 86 degrees F in low mode and will kick to high mode when the temp reaches 104 degrees F. the fan uses an internal 12 volts DC from the GTN. the only time I've seen this issue is when there is a low voltage condition to the unit and this additional drain of current may cause some odd issues like this.
we've not had any other reports of this and the first recommendation I'd make at this point is to check the main voltage input to the unit and see if there could possibly be a low voltage condition. If this is happening on a continual basis I'd then have your local Garmin dealer take a look at it to verify there is not some other problems that may be inducing this.

Please feel free to contact me with any questions,

Ground plane?

Trek can you elaborate on the ground plane issue? First I've heard of this. I've been helping a friend install one in a glass plane and we may need to do something different here.
Thanks Tim

Response from Garmin

Hi all,

I went to Garmin Support and they mentioned that I should go to my dealer and have them replace the fan and check the wiring. My Dealer is Stein, so is this something that should be covered by warranty? Would Stein send me a new fan? Not sure what to do here, but I will follow up with Stein if he doesn't see this post.

Regarding other feedback, yes my ground plane is large as I have the antenna on my Turtledeck, also, plenty of cable length, and I used the -400 cable vs. RG-58. All is good there and this is not an antenna issue.

Also, I am using the VP-X and have plenty of Power. I can see my system power and the draw being used by my components. There is ample power being supplied to the GTN.

Also, I am going to try to get a video of the fan kicking on (audible) and then the following signal loss. This time of year, it does it fairly quick since that 86 degree mark is usually hit a couple minutes after the unit is powered on.

Thanks

704CH said:

Hi all,

Also, I am using the VP-X and have plenty of Power. I can see my system power and the draw being used by my components. There is ample power being supplied to the GTN.

Thanks

Click to expand...

I think the suggestion was to check for a poor connection or damaged power wire between the VPX and the GTN, e.g., confirm you have 12.6 volts at the GTN's rear connector, with the fan on.

Hello everyone,
one other thought one of our GPS antenna engineers thought of as well is to check the crimps on the coax's to the antenna and the GTN unit for the center conductor as a poor or marginal connection could cause some GPS voltage sag at the antenna.