Hello, I've got a Hornby J52 and a Hornby Bill (from the TTTE range) which seem to have their wheels not connected to the motor, since i hear it spinning. I don't know how to fix it. The J52 worked fine till a few days ago, now there's a low chance of it moving. While Bill just didn't move at all. Is there any way i can fix them? How do i find the problem?