What was found
GUM - FLT 0975 - L/P 7963825 - AT APPROXIMATELY 25 MINUTES OUT AFTER TAKEOFF, CREW ADVISED CABIN CLIMBING AT 400 FEET PER MINUTE WITH AIRCRAFT AT FL 29.0. UNABLE TO CONTROL PRESSURIZATION AT ALL MODES AUTO/STANDBY/MANUAL. MAINTENANCE TROUBLESHOT SYSTEM AND REPLACED CABIN PRESSURE CONTROLLER PER MM 21-31-00. GROUND CHECKS OK. MAINTENANCE REQUEST CREW FOR EVALUATION AND SUBSEQUENT FLIGHTS. ALL SYSTEM WORKS NORMAL. (X)