What was found
AT GATE: MAIN CARGO DECK FIRE INDICATED FOR 10 SECONDS. EICAS, DISCRETE LIGHTS, AURAL WARNING , CREW PERFORMED QRH AND PULLED EVERYONE FROM AC AND CALLED ARFF THEY CLEARED FOR REENTRY AND WAS SUSPECTED FALSE WARNING .AFTER LOADING RESUMED A SECOND FULL FIRE WARNING OCCURED =. AC WAS GROUNDED AT THIS POINT FOR EVAUATION MTX . REMOVED PRINTED CIRCUIT CARD M10427 (P/N:285N0028-136, S/N:D19762) AND INSTALLED AT POSITION M2026,IAW AMM 26-10-01. PREVIOUS FIRE/OUHT LOGIC TEST CARD M2026 (P/N:285N0028-136, S/N:D19502) WAS REMOVED. INSTALLED CIRCUIT CARD M10247 (P/N:285N0028-21, S/N:D02850) REF AMM 26-10-01. C/W AFOLTS CARD INSTALLATION TEST REF AMM 26-10-01. NO FAULTS NOTED. THEN CHEKED GROUND INTEGRITY AT MODULES TEST/ALARM INTERFACE MODULES M12276, M12277, M12278,M12279, M12284, & M12285 PINS 1,RD 26 RESPECTIVELY NO ISSUES NOTED. THEN GRND AT CONNECTOR D7990 PIN 5U (A7 P54 PANL) & CONNECTOR D 10106 PIN FAULTS OBSERVED. THEN C/W MC COMPLY SMOKE DET SYS TEST REF AMM 76-14-00, WITH SMOKE DET 1C2B (D31452) & 2C2B (D31424) DISCONNECTED GREEN LIGHTS ON A M12277 & M12279 RESPECTIVELY, TIGHTENED CONNECTORS, D31520 & D31424, NEW INDICATIONS WORKING PROPERLY. UNABLE TO DUPLICATE ON GROUND, SYSTEM OVERIDING OK. REF 56M 26-16-03. DEFERRED MDE COMPT SMOKE DET SYS PER MEL 26-16-2. PLACARD INSTALLED MB2B 10-22-24. A/C REMAINS NO ETOPS.RETURNED AC TO SERVICE .