MX2 not communicating to Sandia transponder
Posted: Thu Jun 12, 2025 9:15 pm
I bought a MX2 a few months ago to replace my ageing Discovery Lite. I made a convertor cable to go from the 25 pin MX2 connector to the existing wiring in the airplane. My problem is that it will not communicate correctly to my Sandia 165 transponder. It seems to recognize there is something out there since it shows code 7777. But I cannot change the code. I'm in the US, so I worked with Michigan avionics support to troubleshoot the problem, but so far there has been no solution. I've changed serial ports, flipped RX/TX, and used the MX2 serial port test function to validate the wiring all the way to the transponder. We've tried 2 software versions. I continue to fly with my old Discovery Lite which continues to communicate correctly with the transponder. If I had a scope the problem would be apparent pretty quickly, I think. But I don't really want to burn a couple hundred dollars on a scope I would use once. I'm at a loss as to what to do next. I appreciate any ideas.