What was found
IN CRUISE, FL 290 MAIN DECK CARGO FIRE WARN LTS ILLUM STEADY. EMER ACTION AND LANDING CARRIED OUT. FUEL JETTISONED IAW CHECKLIST. MAIN DECK CARGO SMOKE DET LTS ILLUMINATED STEADY ON DESCENT, WENT OUT AND CAME ON INTERMITTENTLY THROUGHOUT DESCENT UNTIL THEY REMAINED OUT AFTER 10,000 FEET. DIVERTED, FUEL DUMPED +/- 40.8 TONS. C/A: MAIN DECK CARGO FIRE DETECTION A AND B CONDITION CHECKED OK. FLIGHT, DPS/MEL ITEM REPEATED ON DESCENT. MAIN DECK CNTRL PANEL CHECKED AND TESTED OK. ALL SMOKE DETECTORS ON MAIN DECK CHECKED, OK. FIRE WARNING LIGHTS ILLUM ON TAXI IN. UNABLE TO DUP DEFECT ON GROUND REPLACED CONTROL MODULE IAW MM AS PRECAUTION. ALL SMOKE DETECTORS ON MAIN DECK CHECKED AND SYS TESTED OK IAW MM.