As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN TESTING FIRE DETECT LOOPS, ENGINE NR 1 FIRE WARNING LIGHT ON MASTER WARNING PANEL WILL NOT COME ON EITHER ON -A- OR -B- LOOPS. REPLACED MASTER WARNING CONTROLLER AS PER M/M 33-15-11. OPS CHECKED NORMAL. TEST PER M/M 33-15-00. OK FOR SERVICE.