As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER PULLING & RESETTING CB L15, L16, C6 & T18, CREW REPORTED A PRONOUNCED BURNING PLASTIC SMELL WAS EVIDENT ON THE FLIGHT DECK. THE SMELL CONTINUES TO LINGER 15 PLUS MINUTES AFTER FIRST NOTICED. ACCOMPLISHED TSM 05-50-00-810-831-A & FOUND SOURCE OF ODOR COMING FROM APU BLEED. ACFT WAS RELEASED ON MEL 49-10-01A. RAN APU FOR APPROX 3 HOURS IN BLEED MODE & RAN BOTH PACKS IN COOL & HOT. NO SMELLS NOTED AT THIS TIME. THIS CLEARS MEL 49-10-01A.