As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING TAXI OF ACFT, SMOKE WAS NOTICED COMING OUT FROM FACE OF TRANSPONDER. ACFT WAS SHUTDOWN & MAIN BASE NOTIFIED. AN INSPECTION WAS CARRIED OUT FROM A LOCAL AMO & DETERMINED TO BE AN INTERNAL PROBLEM WITH THE TRANSPONDER. THE UNIT WAS REMOVED & ACFT PROCEEDED WITH INTENDED FLIGHT BACK TO MAIN BASE.