What was found
ON PREFLIGHT, FLAPS VISUALLY APPEARED TO MOVE FREELY BUT FLAP INDICATOR HESITATED AT 12 & 20 DEGREE POSITIONS. AT 12000', STRAIGHT & LEVEL, SLATS, KRUEGERS & FLAPS ALL WORKED PROPERLY. AT 12000', LEVEL BUT TURNING, SELECTED FLAPS 12 & GOT "SLAT/FLAP MX" EICAS & NO MOVEMENT OF SLATS, KRUEGERS, OR FLAPS. RECYCLED HANDLE, & AGAIN NO MOVEMENT. ALSO TRIED SLAT BYPASS SWITCH, SAME EICAS MESSAGE BUT NO SLATS. CHECKED INTEGRITY OF WIRES ON FLAP/SLAT HANDLE. REPLACED CIRCUIT BOARDS 645 AND 82P. R & R LT AND RT NR 3 SLAT ACTUATORS IAW CMP 275227 AND CMP 275228. COMPLIED WITH FLAP/SLAT CONTROL DRIVE FUNCTIONAL TEST IAW CMP 275101 WITH NO FAULTS NOTED.