As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IN FLT AFT LOOP A FAULT LIGHT ILLUMINATED AND EXTINGUSHED TWICE. MAIN DECK CARGO FIRE WARNING CAME ON NEXT. DURING RETURN TO PDX WARNING EXTINGUISHED. REPLACED MAIN DECK CARGO COMPARTMENT SMOKE DETECTION CONTROL UNIT 50WU 3 IAW MM 26-19-34-0401 AND 26-19-00-0501. SYS OPS CHECKS OK IPC 2 6-19-08-02.