As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ATC ASKED PILOT SEVERAL TIMES TO TURN OFF THE ALTITUDE PORTION OF THE TRANSPONDER BECAUSE OF ERRONEOUS CODE. BENCH CHECKING, CODE ERRATIC AND BLANKING IN SOME ZONES. CODE TRACKS FOUND TO BE ECCENTRIC RELATIVE TO THE SHAFT PIVOTS. SUBMITTER STATED THIS WAS A FACTORY SEALED INSTRUMENT AFTER CODE DISC MADE CONCENTRIC, CODE OK.