What was found
IAH- FLIGHT 3668, ON CLIMB THE CREW NOTED THAT THE CABIN ALTITUDE AND RATE WERE MISSING, AND THE CREW WAS UNABLE TO CONTROL THE CABIN ALTITUDE. THE CREW RETURNED THE AIRCRAFT TO IAH WITHOUT INCIDENT. MAINTENANCE REMOVED AND REPLACED THE NR 1 IC600 COMPUTER, PERFORMED A OPERATIONAL CHECK, NO DEFECTS NOTED. THE AIRCRAFT WAS APPROVED FOR RETURN TO SERVICE.