Need help! GTN to Dynon transponder for ADSB position

Back story: Plane finished in 2014, flew great for 2-3 years. I'm pretty sure I did a software update on the dynon transponder and the next day when I went to fly, prior to take off I noticed it said there was no GPS position. I changed the transponders position input to the GPS250 and have been flying it that way since. When it first occurred I researched and called dynon and they said the wire is broken. I didn't believe that since it worked fine the day before but I checked and couldn't find a loose or broken wire anywhere. End result I gave up working on it. Today I dug the wire out from the GTN connector to the dynon connector and even cut open my heat shrink and replaced the resistor. The wire wasn't broken but I was hoping it was fixed. NOPE, same sad story. I called dynon and they suggested maybe a firmware update or possibly the transponder has an issue. I tried the GTN on both of its ADSB-B+ formats which is only selectable under the one serial pin I used. I know the wire is good so its getting to the transponder or at least I think it is. However, if I select it as the source under the transponder setup it still tells me GPS offline. Tomorrow I'm going to try a spare transponder I have to see if that is it but is there anything I'm missing here...Its only the one wire between the two. The GTN and transponder work flawlessly otherwise and it worked fine for the first two or three years. Any help or ideas would be greatly appreciated. Thanks

Your rs232 input for the gps data from the GTN, and out from the GTN, should be set to ADSB+ format. You might call Trig (maker of your transponder) and see what software version you need to read ADSB+.

The Dynon GPS250 is not an ADSB compliant position source. Could that be the issue? Need to upgrade to the GPS-2020. The software might have just caught up with the requirements. Also, there was recently a Dynon SW update to correct a GPS issues, so make sure you have the latest release.

BobTurner said:

Your rs232 input for the gps data from the GTN, and out from the GTN, should be set to ADSB+ format. You might call Trig (maker of your transponder) and see what software version you need to read ADSB+.

Click to expand...

Although TRIG manufactures the DYNON transponder, the internal software is different so he will have to get and do any update from DYNON.

Check and make sure both your GTN and your transponder have the latest software. If they do, keep talking to DYNON and GARMIN since they are your best source.

Good luck and let us know what you eventually find.

There is no issue with running the GPS-250 receiver while using the GTN-650 as your GPS source input to the transponder. That is my normal setup.

As your install has worked before I suspect this problem is associated with the software update. There is one more connection to verify. You already verified the GTN serial out to the transponder (with the inline resistor). Note the GTN serial out has two connections, the serial out and the serial low. For the transponder serial low is aircraft ground. For it to work you need to take the GTN serial low needs to be connected to aircraft ground.

Carl

Carl, I sent you a PM.

Nick,

I have similar config in my RV-10, except that I have AFS screens.

It's going to be hard to troubleshoot remotely. Sometimes its good to get a second set of eyes on the situation. Sometime a near person will see things you don't because your too close to the situation.

It's got to be one of the following:

1. wiring issue - open, short, or wrong pins (it's not hard to be off by one pin on the high density connectors)
2. port software config - not set to the appropriate setting
3. efis/transponder software version - make sure you are on the latest release

bob

Problem solved

It was the serial ground as Carl suggested. Thanks for all the responses and ideas.