As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IT WAS REPORTED FROM AIR TRAFFIC CONTROL (ATC) THAT THE AIRCRAFTS NR 1 TRANSPONDER SYSTEM WAS NOT TRANSMITTING MODE C ON MULTIPLE LEGS. THE MAINTENANCE VENDOR FUNCTIONAL CHECKED THE SYSTEM AND WAS NOT ABLE TO VERIFY THE DISCREPANCY ON THE GROUND. ALL TESTING PASSED. THE AIRCRAFT WAS RETURNED TO SERVICE.