As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE, MAIN DECK CARGO SMOKE DETECTOR NR 4 CARGO FIRE LIGHT AND MASTER FIRE WARNING CAME ON. THERE WAS NO SMOKE OR FIRE VISIBLE ON MAIN DECK. LIGHT STAYED ON UNTIL 12,000 FT ON DESCENT FOR LANDING (ON STEADY FOR 20 MIN). FLIGHT CONTINUED ON TO NRT, AND LANDING WAS UNEVENTFUL. MAINTENANCE REMOVED AND REPLACED BOTH 4A AND 4B MAIN DECK SMOKE DETECTORS PER MC REQUEST. OPERATIONAL CHECKED GOOD, AND AIRCRAFT RETURNED TO SERVICE.