What was found
WHILE IN CRUISE AT FL250, THE CABIN ALTITUDE WENT TO 12,000 FEET. CREW ACCOMPLISHED AN EMERGENCY DESCENT TO 9,000 FEET AND LEVELED OFF. MASKS DID NOT DEPLOY AND FLIGHT CONTINUED TO DESTINATION. LANDING AT BUF WAS UNEVENTFUL. CREW STATED THAT THE MANUAL SPRING WAS BROKEN. MAINTENANCE REPLACED THE AUTO PRESSURE CONTROLLER, THE CONTROLLER AMPLIFIER, AND THE DIFFERENTIAL SENSOR. AIRCRAFT ENTERED INTO L-CHECK AT DHN.