As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: DURING BOARDING EXTERNAL POWER CAUGHT FIRE, AIRCRAFT HAD A HARD CHANGE OVER TO APU POWER, SUBTLE SMELL OF ELECTRICAL SMOKE IN COCKPIT, UNSURE OF EXTERNAL POWER DAMAGE. MAINTENANCE REPLACED GROUND AUX PANEL CONTROL UNIT AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK PER AMM 24-41-34.