What was found
(CAN) ATB DUE TO UNABLE TO RETRACT ALL LANDING GEARS JUST AFTER TAKEOFF, THREE RED GEAR UNSAFE/ON TRANSIT LIGHT ILLUMINATED, ALSO THE DRAG NOISE WHEN THE GEAR WAS DOWN WAS STILL THEIR.SO WE ENTERED A HOLD. PERFORMED AN ALTERNATE EXTENSION - GOT THREE GREENS. AIRCRAFT WAS TRIED ON JACK AND UNABLE TO RETRACT ALL LANDING GEARS. MAINTENANCE REPLACED LANDING GEAR SELECTOR PANEL, FUNCTION TEST CARRIED OUT, GEARS RETRACTED NORMALLY, A/C RTS (TC# 20190826022)