What was found
(CAN) FLAP HALFSPEED MESSAGE ON TAXI OUT - EXTENDING FLAPS FROM ZERO OT 8. CB RESET OK. AFTER TAKEOFF ON RETRACTION FLAP HALFSPEED MESSAGE CAME BACK. DECISION TO RETURN A/C TO AIRPORT. (FLAP SKEW DET. SYSTEM. M TO DEACTIVATE) MAINTENANCE FOUND FLAP POWER DRIVE UNIT (PDU) LT MOTOR/BRAKE FOUND TO BE FAILED. FLAPS PDU ASSY REPLACED IAW AMM 27-52-01. FLAPS SKEW DUMMY BOX REMOVED AND ORIGINAL SKEW DETECTION UNIT P/N 80-043-01 S/N A957 RE-INSTALLED AND FUNCTION CHECKED SERVICABLE. FLAPS SYSTEM OPS CHECKS CARRIED OUT AND GROUND CHECKS SERVICABLE. RII COMPLETED ON FLAP PDU ASSY FOR SAFETY OF INSTALLATION.