The smaller wheel is the idler wheel. Check it to be sure that it is indeed hard like plastic. I've never seen one in that condition, unless it's been stored in some old shed somewhere. Sometimes, a light sanding and some rubber renew will bring it back to life.
The larger wheel is for the change cycle and works off the motor, too. The changer will cycle even when the platter is removed. Maybe it's stuck and that's why you can't use the auto function. Look at those links for both wheels and see if you can move them.
Click on the file name, not the pic, or it will be too big.