Our playskool train will not move forward
Had the same problem - the train at first stopped moving, but still rotated the balls, then later stopped rotating the balls at all. The music still played, though. I found the issue to be a small belt that transfers the motion from the electric motor to the gear system. The belt is tiny (think small rubber band) and lost tension, finally detaching from the system altogether. Getting to it is the difficult part... mind you that taking it apart carries a very high risk of breaking the plastic, so be prepared to scrap the whole thing and buy new.
To fix, start by removing the 7 outside screws to essentially split the train body in half. You'll have to pry off the large green wheel that's opposite the screws (right side of train) - this part carries the highest break risk. Be mindful of a spring (about 1/2 inch diameter) that may go flying - that one goes on the outside of the little inside wheel that moves the balls around.
Once the train is split in half, remove all screws you find, which will allow you to remove the mechanical sections, which includes the battery pack, electric motor, on/off switch, and gear system, including the wheel that moves the balls around. By the time this entire section is lifted off the train body, you'll see where the gears (they're a bit greasy) are attached to the motor towards the bottom of the gearbox. The gearbox itself has 3 or 4 screws to address that will reveal the entire gear system.
I had to take the lower (smaller) gears apart in order to replace the gear belt.
Replace the gear belt with a small rubber band (you'll likely need a small screwdriver to wrap it around the wheels), then re-assemble the gearbox and system. i recommend constantly running the toy with every step to make sure everything's still connected.
with a healthy rubber band/belt in place, the rest of the gear systems will fall into place with enough torque to drive both the train movement and the ball wheel.
good luck
