What was found
ON FLAP RETRACTION AFTER TAKEOFF, FLAP MOVEMENT STOPPED BETWEEN FLAPS 1 AND FLAPS UP AND A "LEADING EDGE ASYMMETRY" EICAS MESSAGE WAS DISPLAYED. SYSTEM THEN TRIGGERED A "FLAP ISOLATION VALVE" STATUS MESSAGE. COMPLIED WITH COM PROCEDURS AND RECEIVED A "LEADING EDGE DISAGREE" MESSAGE AFTER SELECTING ALTERNATE FLAP SYSTEM. FLIGHT DECLARED AN EMERGENCY, RETURNED TO LAX, AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED THE FLAP SLAT ELECTRONICS UNIT. SYSTEM OPERATIONAL TESTS WERE SATISFACTORY.