As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN DISCONNECTING THE GROUND POWER UNIT, THE GPU AVAILABLE LIGHT AND ALL CABIN LIGHTS STAY ON. SHORTLY BURNT SMELL APPEARS MAIN BATTERIES DISCONNECT FOR SAFETY. TROUBLESHOOTING CARRIED OUT, FOUND DIODE CR046 AND SOME WIRES BURNT, CR0465 SHORT CIRCUIT AND THE BACK UP BATTERY VOLTAGE TOO LOW. DIODE REPLACED AND WIRING REPAIRED. FUNCTIONAL CHECK OF ALL AFFECTED SYSTEM IN PROGRESS.