What was found
NR 1 ENGINE FIRE PULL HANDLE DOES NOT ILLUMINATE DURING TEST. ACFT GROUNDED. DUPLICATED PROBLEM, IAW MAINTENANCE CONTROL, DUE TO CHRONIC HISTORY, REMOVED AND REPLACED ALL FOUR DETECTOR ASSEMBLIES IAW AMM 26-11-01-000-802. AFTER CHANGING DETECTORS M1757, M1758, M1759, AND M1760 OPS CHECKED GOOD. AFTER ENGINE RUN GROUND FUNCTIONAL CHECK OF ENGINE FIRE DETECTION SYSTEM WAS GOOD IAWAMM 26-11-00-710-801.