Transponder error

[Max_Gieseke]

Just installed a rebuilt D10A into my RV6 as the old D10A got fried. Dyson was very good at getting me a replacement. Using a grays converter for my Terra transponder I am getting a large error when checked against the local Class B approach radar. Format is set to "1". ATC tells me that my Mode C is showing 800' when I am actually over 4500'. Any advice?

 

[dynonsupport]

Unfortunately, the advice is that you must get a transponder check. This is why the regs state that any time you change anything having to do with the altitude encoder, you must have it re-certified.

The way the gray code works, you likely have a single broken wire, which will lead to the altitude being right at times and very, very wrong at other times. An avionics shop can tell quickly which wire is broken by going through different altitudes.