What was found
AT 35,000 FEET, EXPERIENCED CABIN ALTITUDE ALERT WARNING. CREW WAS UNABLE TO CONTROL CABIN PRESSURE USING STANDBY OR MANUAL MODES. INITIATED EMERGENCY DESCENT TO 15,000 FEET WHERE CREW REGAINED CONTROL OF PRESSURE. AIRCRAFT MADE AN UNEVENTFUL LANDING AT SJC. INSPECTED AND PERFORMED PRESSURE CONTROL TEST WITH NO DEFECTS NOTED. REPLACED MAIN OUTFLOW VALVE, O/H PRESSURE CONTROL PANEL AND PRESSURE CONTROLLER PER BOEING M/M.