Sounds as if the little electronic phase control board has had it. You can find one on ebay (make sure it is for 110 volts). The Service Manual can be found at:
https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.kitchenaidparts.eu/documents/pdf/service-manual/classic-svc-manual-new-email-version.pdf&ved=2ahUKEwiCxJD44M3rAhWAknIEHYjGBMEQFjABegQIBBAB&usg=AOvVaw1VD7tqAQHvjW_d2cjf_nMH