Hi, I've got one of these and it's caused in my case by the central wheels locking up. It must be due to the drive cog or worm. Try this:- gently/slowly drive the wheels round untill they jam or slow down. The stop the loco - slide the central axel to one side and see if it frees up. If it does then you have exactly the same problem as I have. It should not be too difficult to trace the mechanical fault from there. I will add that I do not recommend using the motor or DCC to drive the loco if it's locking up. This is because you will burn the DCC Chip out very quickly as I have done in the past. This is because when a mother stalls then the current shoots up to about 10 times the normal working current, this burning the DCC Chip or even the motor out. Watts are Voltage X Current or
Watts = Volts x Current
Watts are the total power or in this case heat! Heat is the worst thing you want. I hope this helps. Cheers Neil