What was found
DURING CLIMBOUT, MASTER AND PRESSURE WARNING LIGHTS ILLUMINATED WHILE PASSING THROUGH 17,500 FEET. COMPLETED COCKPIT OPERATING PROCEDURES AND GAINED CONTROL OF CABIN AT 4,000 FEET. AIRCRAFT LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED OUTFLOW VALVES AND REPLACED CABIN PRESSURE CONTROLLER. AIRCRAFT WAS PRESSURIZED ON GROUND, OPERATIONAL CHECK OK.