ADSB issue

[Capnrob]

I have a RV7 with GRT HX/HS EFIS and a G430waas. It also had a GTX330 and everything worked great. Then I upgraded the GTX to a GTX330ES for ADSB out and have lost mode C . Two trips to the avionics shop and hours on the phone with GRT, Garmin and the panel builder have not solved the problem. The avionics tech put another ES box in my airplane from a different a/c and mode C worked fine. At that point assuming the mode C was bad I sent it back to Garmin for repair. A week later it's back in my airplane with the settings in the 330ES carefully entered- mode C still inop. Anyone seen anything like this or have some suggestions I might try? Only 11 days until my FAA rebate reservation expires.

[PJM6A]

I'm having a similar problem. Dual GRT Horizon HS. Upgraded transponder to Garmin 330ES, upgraded all software in Garmin 430W. Failed the ADSB validation flight due to no altitude data being received. My avionics shop has not been able to figure it out.

By the way, I'll comment the GRT tech support has been helpful and responsive. Garmin has offered no help whatsoever. Even though 2 of the 3 units involved are Garmin.

Your suggestions are welcome !

[dtw_rv6]

Borrow the working transponder for the qualification flight before the rebate expires.