Can someone describe the intricacies of Mode C?  I didn't install my original panel, but I have done many upgrades (I did not install the Mode C).  I have had it fail before and the avionics shop repaired it.  It failed again a few months ago and I removed the King box and replaced it.  I heard something rattling around in it, so I went ahead and replaced it.  I figured at 150 bucks from Spruce it would be worth a shot to see if that was the problem as opposed to having to fly it to my closest avionics shop an hour flight away and having to leave the airplane, get a ride back, etc etc.  Well needless to say, that's not the problem and I was wondering if you guys had any suggestions.  I haven't had it tested with any ground equipment, but ATC does not receive my Mode C.  It failed during a trip a few months ago.  Thanks for any input.

Steve Reeves
Glasair 1FT 38SR