What was found
CABIN ALTITUDE CLIMBED ABOVE 15K. CABIN ALTITUDE WENT TO 15.000 FT DURING CLIMBOUT. ACFT HAD JUST PASSED THROUGH 10,000 FT AND PRESSURE WENT TO THE YELLOW LINE FOR A FEW MOMENTS, THEN WENT INTO THE RED RANGE. RAN QRH AND ATTEMPTED CONTROL WITH MANUAL MODE WITH NO RESULT. DESCENDED TO 10,000 FT AND RELEASED PRESSURE, LANDED WITH BOTH VALVES OPEN. R & R THE DIGITAL CONTROLLER AND PERFORMED OPS CHECK OF PRESSURIZATION CONTROL OPS CHECKED GOOD AT THIS TIME.