What was found
DURING CLIMB OUT FROM DEPARTURE, UPON SELECTING GEAR UP, ALL 3 GEARS REMAINED DOWN AND THE CREW RECEIVED AN ANTI-SKID IB MESSAGE ACCOMPANIED BY A PARK BRAKE SOV MESSAGE. THE TOWER DECLARED AN EMERGENCY AS A PRECAUTION AND THE AC RETURNED TO DEPARTURE, LANDING SAFELY. MAINT REMOVED AND REPLACED THE PROXIMITY SENSOR ELECTRONIC UNIT (PSEU); AND ALSO CYCLED THE GEARS SEVERAL TIMES. OPS CHECK GOOD. AIRCRAFT OK FOR SERVICE. (K)