As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE FLIGHT CREW REPORTED AN ELECTRICAL BURNING ODOR IN THE FLIGHT DECK, ASSOCIATED WITH POWER TRANSFER BETWEEN GROUND AND APU ELECTRICAL POWER. DURING TROUBLESHOOTING THE GAPCU UNIT WAS DISCOVERED FAILED, THE UNIT WAS REPLACED AND THE AIRCRAFT WAS RETURNED TO SERVICE. INSPECTION FOR ELECTRICAL ODORS WAS ACCOMPLISHED WITH NO FINDINGS IAW AMM-24-0 0-00-810. NO REPORTS OF ODOR ON SUBSEQUENT FLIGHTS.