DISASSEMBLY TO INSPECT OR CHANGE BERNINA 830 MOTOR BRUSHES:
Remove the big plastic cover piece on the bottom of the machine with the single screw in the center.
Remove the machine's end panel by removing the single silver screw from underneath the bottom middle of the side panel. Pull the bottom of the side panel out and down to remove it. It comes off easily.
Remove the two screws under the motor assembly (silver screws with black washers).
Swivel the motor assembly enough to remove the belt.
There is a another plastic panel on the motor assembly over the motor itself. Remove the two phillips head screws to remove this panel.
At this point you can see the commutator and inspect the "business" ends of the brushes. (In our case, one brush was almost gone and there was nothing left of the second brush except the spring!)
You can then slide the motor out of the housing. I pushed on the motor pulley and pulled on the other end of the motor with pliers. The motor comes out rather easily, but be careful not to disturb the wires any more than necessary.
With the motor exposed, unscrew the caps over the brushes and remove the brushes.
Our motor's commutator looks significantly worn and the motor may need to be replaced. If you find a source for the brushes or a replacment motor, please let me know! Thanks, John firstname.lastname@example.org