Originally Posted by
Sheluma
open the controller and check that the full speed contacts come together when the button is depressed all the way
Why didn't I think of that? Great idea. Even if there's carbon dust buildup, it should still work at full speed when fully pressed (mine was also missing one of these, incidentally). Our own archaicarchane was my source of information when I fixed mine:
http://www.archaicarcane.com/singerattheraces/
Mike