As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
TRANSPONDER CONTROL HEAD GIVING INCORRECT ALTITUDE TO TRANSPONDER. THE A2 LINE IS BEING SHORTED TO GROUND BY SOLDER MIGRATION FROM GROUND. THIS IS AT CR-8 CATHODE ON THE A5 BOARD. SUBMITTER STATED THIS IS THE SECOND CONTROL HEAD FOUND WITH THIS PROBLEM.