As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOTS SMELLED A FAINT ODOR OF SMOKE THAT SEEMED TO DISSIPATE AFTER THE ENVIRONMENTAL SWITCHES WERE TURNED ON AND CONTINUED FLIGHT. DURING GROUND CHECKS OF THE ACFT, BY MX, THE FIRE DETECTION SYS WAS FOUND U/S WHICH LEAD TO THE DISCOVERY OF THE CIRCUIT BREAKER BEING FOUND MELTED/BURNED.