As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENROUTE, NOTICED ELECTRICAL FIRE ODOR BRIEFLY. ODOR OF SMOKE FROM TRANSPONDER. SMOKE STOPPED AND ODOR DISRUPTED. NO ISSUES WITH EQUIPMENT OR PLANE, ALL FUNCTIONED NORMAL. R & R ATC/TCAS CONTROL PANEL IAW AMM 34-53-02-004-001. OPS TESTED OK.