What was found
CABIN ALT WARNING AT FL 370. CABIN ALT WARNING AT FL 370 FOUND #1 PACK SUPPLY DUCT AT THE CHECK VALVE ( FWD LEFT PACK BAY) ORANGE SLEEVE AND CLAMPS LOOSE AND NOT SECURED WITH LARGE AIR LEAK. READJUSTED DUCT SLEEVE AND SECURED CLAMPS AND ACCOMPLISHED LEAK CHECK AND PRESSURIZED A/C WITH #1 PACK UP TO 4.0 DIFF PRESS WITH NO FAULTS NOTED. MX ACCOMPLISHED REF 757 AMM 21-51-15-4-0 AND 21-31-00-5. REMOVED AND REPLACED AIR CONDITIONING CHECK VALVE AND BOOT ASSY, REF MM 21-51-15-4-0.