What was found
AIRCRAFT WAS GROUNDED. PILOT REPORTED AT AROUND 6000 FEET, THE SAFETY VALVE WENT TO FULL OPEN, DEPESSURIZATION ENSUED. THE CABIN RATE OF DESCENT GOT TO 1400 FPM. MAINTENANCE RESET FCU IAW TSM 24-00-00-817-818-C1. NO FAULTS, OK FOR SERVICE.