What was found
AFTER TAKEOFF, FLAP RETRACTION, FLAPS WOULD NOT RETRACT (FROM 15/20) UNTIL AFTER LANDING. THEREBY CAUSING AN UNSCHEDULED RETURN TO CWF. TROUBLESHOT IAW TSM 27-50-02 FIG 101/102/103/104. AT ON SITE REP REQUEST SWAPPED NR`S 3/5/6 FLAP SYSTEM JACKSCREWS FROM LT WING TO RT WING, AND ALSO REMOVED AND REPLACED LT NR 4 FLAP JACKSCREW PER CUSTOMER REQUEST. ALSO REMOVED AND REPLACED LT NR 5 DOWN DRIVE SHAFT AND NR 5 LT JACKSCREW, AND RT NR 2 FLAP JACKSCREW, REMOVED AND REPLACED LT FLAP SYSTEM TORQUE LIMITER, SFCC NR 1 AND SFCC 2 COMPUTERS ALL IAW AMM 27-50-00-4; AMM27-50-21-4; AMM27-51-18-4; AMM 27-54-12/22/23/24/25/26/27/28-4 (SUSPECT BAD FLAP JACKSCREW AT NR 4 LT POSITION FROM OVERHAUL VENDOR).