What was found
ENROUTE, AT FL250, THE CABIN ALTITUDE WARNING HORN SOUNDED AS CABIN WAS NOTED TO BE CLIMBING AT 1,200 FEET PER MINUTE. FLIGHT DESCENDED TO FL 080. CREW REGAINED CONTROL OF CABIN PRESSURE USING MANUAL MODE. FLIGHT CONTINUED AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE PERFORMED OPERATIONAL CHECK OF AUTO AND STANDBY PRESSURIZATION MODES. OPERATIONAL CHECK GOOD. REMOVED AND REPLACED CABIN PRESSURE CONTROLLER AND SELECTOR PANEL AS PRECAUTIONARY. CONTROLLED PRESSURIZATION OF CABIN IN AUTO AND STANDBY MODES. AIRCRAFT OK FOR SERVICE.