As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON FLIGHT 4205, CREW REPORTED UPON STARTING APU COCKPIT FILLED WITH ELECTRICAL BURNING SMELL AND SMOKE. AIRCRAFT REMOVED FROM SERVICE. FOUND APU STARTER GENERATOR TO BE DEFECTIVE AFTER REMOVING PIECES OF METAL FROM INSIDE GENERATOR. REMOVED AND REPLACED GENERATOR IAW AMM 24-800-01. APU CHECKS GOOD. NO SMELL OR SMOKE DETECTED. AIRCRAFT RETURNED TO SERVICE.