As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED NR 3 CARGO SMOKE DETECTOR LIGHT ON. MADE A TURN AROUND AND LANDED WITH NO INCIDENT. *S/D* CHANGED NR 3 SMOKE DETECTOR, MAIN CARGO SMOKE PANE AS PRECAUTION. REMOVED AND REPLACED SMOKE DETECTOR MODULE FOR PRECAUTION. CK GOOD PER MM 21-22-00.