As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
TR1 CONNECTOR 1PU1 HAS ELECTRICAL ARCING DAMAGE. ON TAXI IN LOUD NOISE HEARD BEHIND F/O AND CAPTAIN SAW SMOKE BY JUMPSEAT. HAPPENED WHEN APU STARTED. AREA ABOVE TR1 SHOWS EVIDENCE OF SOOT & SMOKE CONTAMINATION. CLEANED CONTAMINATION OF WIRING COMPONENTS REF AIRBUS ESPM. ACP'D VISUAL INSPECTION OF WIRING FOR DAMAGE. NO OBVIOUS DAMAGE NOTED. TR1CB HAD POPPED. REPLACED CONNECTOR 1PU1.