What was found
CRZ FL340, CABIN ALTITUDE WARNING. CABIN APPROX 10,000FT WITH APPROX 200FPM CLIMB, DIFFERENTIAL 6.4 DESCENDED TO FL320 NO HELP DUCT PRESSURE OVER 40PSI. DECDENT TO FL280 REGAINED CONTROL CABIN DESCEND LIGHT WENT OUT AT 8400 CABIN ALTITUDE. 6.0 DIFFERENTIAL. EVENTUALLY DESCENDED TO ABOUT 7,000FT. DB RT PACK MEL CLEARED. PERF VISUAL INSP OF DOOR SEALS, ALL ARE INTACT AND SHOW EVIDENCE OF GOOD SEALING. CHKD OUTFLOW VALVE FOR DEBRIS, NONE FOUND. VERIFIED SMOOTH OPERATION AND FULL CLOSING OF OUTFLOW VALVE. PERF BITE ON CABIN PRSR CONT'S, NO FAULTS - REF AMM 21-31-00-5. NO HIST 90 DAYS.