What was found
ON CLIMBOUT PASSING ABOUT 3,000 FT FIRE WARNING BELL SOUNDED WITH NO ASSOCIATED LIGHTS. ALL SYSTEM INDICATIONS WERE IN THE GREEN. ALL ENGINE INST INDICATED NORMAL. LOWER CARGO SMOKE, CARGO SMOKE AND ENG AND WHEEL WELL FIRE DETECTIONS SYSTEM ALL TESTED WITH GOOD RESULTS. ON GROUND THE APU FIRE WARNING TEST WAS GOOD. REMOVED AND REPLACED ALL 3 FIRE & OVERHEAT DETECTION POWER UNITS, PER STANDARD PRACTICES. REMOVED AND REPLACED FIRE DETECTION CONTROL BOX PER 20-10-017-2, SYSTEM TEST NORMAL AMM 26-11-000-0. ALSO FOUND SEVERE CORROSION AT THE R-421 BLOCKING RECT CONN D4858, CLEANED. ALSO REMOVED AND REPLACED NAME-FIRE & OVERHEAT DETECTION POWER UNITS P/N 1011C.