As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT#778, LAS-BOS.(ETOPS) "ENG 1 FIRE LOOP B FAULT ( ENGINE FIRE DETECTION SYSTEMS 2) LOOP B ); (RESOLVED ON W/O: 1424411 TASKCARD: NR-00001) REMOVED AND REPLACED ENG #1 CORE LOOP B PER AMM 26-12-17. NO FAULTS NOTED. OPS TEST SATISFACTORY. THIS CLEARS MDDR 587397 MX4 UPDATED PLACARD REMOVED. REF ITEM #1 OF LP 4225103 GROUND VERIFICATION."