If it works better when you twist the loco or put a little pressure on it, then. Open up the area with the pick-ups. Make sure the wire is connected well. I then strip some wire from a scart lead (the fine wire not the thicker one.) Lay it across the stub on the chassis pick-up. Put it back together. You should have 2 or 3 fine copper wires between the stub and the copper contact. This corrects the problem. Well it has for me.