What was found
CREW REPORTED-CRUISING AT FL360 WE FELT OUR EARS POP DUE TO A CABIN PRESSURIZATION ISSUE FOLLOWED BY A MASTER CAUTION AND OBSERVED THE CAB ALT IN RED SHOWING 13500. IMMEDIATELY DECLARED AN EMERGENCY AND BEGAN A RAPID DESCENT TO 14000 WHILE TAKING MANUAL CONTROL OF THE CABIN PRESSURIZATION. THE BEST RATE WE COULD OBTAIN WAS -450 FPM UNTIL IT STABILIZED AT 6500 CABIN ALTITUDE. NO OTHER ISSUES DURING DESCENT TO LANDING AT SDL. CORR ACTION- MX TROUBLESHOT TO BAD OUTFLOW VALVE. REMOVED AND REPLACED ELECTRO-PNEUMATIC OUTFLOW VALVE OPS CHECK GOOD, NO DEFECTS NOTED.