What was found
AIR TURN BACK - FLT 0051 - ON CLIMB OUT OF LAS EN ROUTE, RECEIVED AVIONICS VENT SYSTEM FAULT, AIRCRAFT PRESSURIZED NORMALLY, TURNED BACK TO LAS AND LANDED WITHOUT FURTHER EVENT. MAINTENANCE ISSUED MEL 21-26-04 COND 1, "SKIN AIR OUTLET VALVE INOP". ON 05/31/2004 IN BOS: MAINTENANCE REMOVED AND REPLACED SKIN AIR OUTLET VALVE IAW AMM TASK 21-26-53-000-001, OPERATIONAL CHECK WAS GOOD. FUNCTIONAL TEST OF SKIN AIR OUTLET VALVE S/N 47 WAS NO FAULT FOUND. REMOVED ACTUATOR (S/N 188) AND TESTED ON ACTUATOR BENCH, NO FAULTS FOUND, REINSTALLED ACTUATOR. RETESTED UNIT AND RETURNED TO SERVICE IAW CMM 21-26-53, REV. 6.