I tried to look for a scheme but could find one here, and on google a scheme doesn't pop up ether but there must be one online somewhere.
Having one makes is a lot easier to understand what all the things on the inside are for.
Anyway, I would first look at the 33 1/3 ,45 switch. Clean the inside and make sure it works properly. Then take a look at the pot meters (the speed control thing)
I have a Technics table with the same problem, did not figure it out jet