My Kitchenaid K5-A mixer motor is smoking, how do I fix it?

I inherited a really nice Kitchenaid Mixer, Model K5-A, that has had little use until we brought it home. Just recently, it has been working fine. Then my wife tried to mix cookie dough and smoke started to come out of the motor area. I would like to fix the mixer, since it is such a nice one, but I don't know where to begin. Does anyone have any ideas as to why the motor would start smoking? Any help or advise would be appreciated.