As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT BOTH TRANSPONDERS 1 AND 2 FAILED. A BURNING ODOR WAS NOTED IN THE FLIGHT DECK WITH GPS LEFT FAILURE AND BOTH CLOCKS BLANK. AIRCRAFT RETURNED TO GATE. MAINTENANCE REMOVED AND REPLACED TRANSPONDER PANEL IAW AMM 34-53. OPERATIONAL CHECK OK, AIRCRAFT RETURNED TO SERVICE.