Next time you are working on an old Bally (or Stern) put a piece of paper in between the EOS contacts and see what happens...

If the EOS is open then the power is going through the power coil and the hold coil.  This is usually insufficient power to move the flipper at all (but if you raise the flipper by hand it will 'hold').  If the contacts are burned they will sometimes conduct some power and allow the flipper to operate but below full force.

cheers
Ian