What was found
LE SLAT ASSEMBLY ON UPPER EICAS IN FLIGHT. THIS WAS PRECEDED BY THE FLAP INDICATOR NEEDLE RAPIDLY CYCLING BETWEEN UP AND THE MID RANGE POSITION BETWEEN UP AND 1. WHEN MOVED THE FLAP HANDLE FROM UP TO 1, THE LE SLAT ASSYM CAME ON UPPER EICAS WITH MASTER CAUTION. SLATS WERE LOCKED OUT FOR LANDING. BITE CHECKED PROXIMITY ELETRONIC UNIT, MCDP AND FLAP/SLAT ELECTRONICS UNITS, NO FAULTS LOGGED LAST FLIGHT LEG. INSPECTED LEADING EDGE SLAT POS SENSORS FOR OBVIOUS DEFECTS, NONE FOUND. ACCOMPLISHED BITE CHECKS OF THE PSEU AND FSEU PER MM 32-09-04-4, 27-51-01-4 ALL TESTED NORMALLY WITH NO FAULTS. SUSPECT FSEU AT FAULT, REPLACED SAME REF MM 27-51-01-4, AND OPS CHECKED NORMAL PER MM 27-51-01-4, 27-51-45-2-0. CYCLED FLAPS SEVERAL TIMES WITH NO ABNORMAL INDICATION AND NORMAL OPERATION.