I have a PC 3x21 inch belt sander with variable speed. It seems like there is no ddifference in speed change no matter what the dial is set at, so I just run it at full speed. I am asumming the speed control is broken. Any ideas on how to fix it? A replacemetn part is $50.00, and not really worth it since I rarely need a low speed anyway. Could I just add a router speed controller to it? I know using rounter speed controllers on routers that have VS built in is a bad idea, but it is the same concpect on a belt sander? Could I just by-pass the VS control and use the add on. Or should I just not worry if my belt sander is just single speed?