My son in law's machine had the same problem. I took off the cover of the machine by removing the four star screws. This exposes the motor. There are two brush assemblies on the top of the motor, one on each side. You can remove the brush by loosening a single star screw. I found that one of the brushes was not moving freely in its sleeve. I very lightly filed the brush to allow it to move freely, reassembled the brush assembly and the motor runs. The question is how long will it continue to run. There seemed to be more arcing at the brushes than seems healthy. If you want a good diagram of the motor, there is one at toolpartsdirect.com.
poppahess
November 2006