What was found
FLIGHT 2170. ON POWER UP, AFTER FIRE EXTINGUISHER TEST, ALL LIGHTS ILLUMINATED AS NORMAL, BUT EICAS MESSAGE APPREARED: CRG FIRE PROT FAULT.. REMOVED FROM SERVICE. PERFORMED FIM TASK 26-15-00-810-804-2 THROUGH STEP 7.Q. EXCEPT CONTINUITY CHECKS P0449-C TO P0778-BP1-11 + P0993-BP1-14. RECONNECTED ELECTRICAL CONNECTORS FOR TURNOVER. REPLACED AFT CARGO SMOKE DETECTOR IAW AMM 26-15-01-000/-400-801-A, DID NOT FIX. REINSTALLED ORIGINAL SMOKE DETECTOR PER AMM. VERIFIED SMOKE DETECTOR INSTALLATION & FOUND CONNECTOR P0449 NOT FULLY SECURE. RESECURED P0449. IN COCKPIT FOUND "DC BUS TIE" SWITCH IN OFF POSITION. PLACED SWITCH BACK TO "AUTO". POWERED ON A/C. FAULT NO LONGER PRESENT. PERFORMED FIRE PROTECTION SYS TEST IAW AMM 26-00-00-700-801-A. OPS TESTED NORMAL. NO FURTHER DEFECTS. RETURNED TO SERVICE. NO PARTS REPLACED