As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE, THE MAIN DECK FIRE WARNING BELL SOUNDED AND LIGHT ILLUMINATED. AIRCRAFT DECLARED AN EMERGENCY AND DIVERTED TO YWG AND LANDED WITHOUT INCIDENT. REPLACED THE MAIN DECK 1B FIRE DETECTOR AND TEST SWITCH. OPERATIONAL CHECK GOOD.