I am looking for an exploded diagram of the spectrum 4-4-0 engine.  Specifically I need to see the wheel set assembly for the drivers.  I took mine apart to fix some wiring issues and replace the motor/gearbox assembly and now my wheels are out of gauge and I can't figure out why.  I don't think I left any parts out....but then you never know.  The website does not seem to have anything on it about this engine and the book that comes with the engine does not have enough detail for what I need.  Does anyone know if there is even such a diagram with this level of detail? 
Thanks,
Ed

Kevin:
Thanks a lot for your quick and informative reply. I will remove the pcb since I am using R/C.  I wish these manufacturers would include some basic information in with the after-market products they supply.
Ed

Just received my new motor for this engine and noticed the original motor had no pcb on the end like the new one has.  Can you tell me what the function of this pcb is?