What was found
CABIN PRESSURIZATION FAILED DURING CLIMB. AUTOMATIC PRESSURE CONTROLLER NR 2 WAS IN USE. AUTOMATIC PRESSURE CONTROLLER NR 1 WAS ON PLACARD. EMERGENCY DECLARED, FLIGHT LANDED WITHOUT FURTHER INCIDENT. THE AIRCRAFT WAS GROUNDED. MAINTENANCE ACCOMPLISHED FIM 21-30-00, FOUND THE NR 2 AUTOMATIC PRESSURE CONTROLLER WOULD NOT WORK ON POWER. REPLACED THE NR 2 CONTROLLER IAW AMM 21-31-02, AND PERFORMED A SATISFACTORY OPERATIONAL CHECK.