As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING THE REPLACEMENT OF THE DAMAGED CB 11DA3 (NRC 21423-0291), WE FOUND A SERIOUS CASE OF ARCING BEHIND THE CB-PANEL 721VU. SUSPECT THAT THE LOSE ATTACHMENT PLATE CREATED A SHORT CIRCUIT BETWEEN THE CIRCUIT BREAKER 27TD AND THE AIRCRAFT STRUCTURE.