As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INSPECTION TYPE:N/A STARTED APU N2 GOT TO 25% - 30%. THE AVIONICS SMOKE LIGHT Y BELLS CAME ON AND SMOKE ENTERED THE FLT DECK. SHUTDOWN APU AND BATTERY SMOKE STOPPED. REF TSM 21-20-00. OPERATED A/C ELECTRICAL SYSTEM ON GROUND. ENG NOT RUNNING. A/C AND DC OPS GOOD. RAN APU AND PNEUMATICS. COULD NOT DULICATE CONDITION. SUSPECT EXTERNAL FUME INGESTION.