What was found
LT ENGINE FIRE LOOP 1 STATUS MESSAGE IN FLIGHT FL 320. PERF FIM 26-11 FT 804 SUSPECT AFOLT NR 1 (M10224) CARD AT FAULT. P/N 285N0021-36 ON ORDER. TRANSFERED TO MDDR NR 135892, IAW MEL NR 26-11-01-01, CAT C, DUE DATE 21OCT20. PLACARD INSTALLED. TROUBLESHOT LT ENGINE FIRE LP 1 MESSAGE, PER FIM 26-11 804. SYSTEM LOOP INSULATION RESISTANCE BELOW MIN (20KOHMS), PER BLOCK 3 OF FIM. NO DAMAGE FOUND TO DETECTORS, BUT ALL HAD LOW RESISTANCE FROM "A" TERMINAL TO GROUND. DMI CONTINUES. PERFORMED FIM TASK 26-11 FT 804. RE-RACKED FIRE DETECTION LOOP CARD, CHECKED ALL BLEED DUCT COUPLINGS, AND REPAIRED AS NECESSARY (REF ITEM M-9). DETERMINED ROOT CAUSE TO BE RUPTURED DUCT (REF IREM M-9). PERFORMED HIGH POWER RUN FOR 15 MINUTES, PER AMM 71-00-00, OPERATIONS CHECK NORMAL, NO FAULTS.