you need to test the motor and see if the insulation value to earth is low.this requires a test meter.sometimes you can see segments on the motor discoloured/lifted when brushes removed.difficult to know if pcb has been damaged from your description.Always worth bearing in mind though!!.Motor or pcb are going to be expensive.If it's any age it might be time to invest in a new one!!
CK
February 2013
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