I replaced the speed control board as my mixer was running 3X as fast at setting 1, and topped out at setting 3, with no appreciable increase in speed up to setting10. Yet when I replace the speed control board, there is no change in the performance. Clearly the speed control board is not the problem. Yes I did adjust the upper screws in to slow and out to speed up, and the bottom screw as well. No significant effect. Mixer "rolls" at any speed; not keeping an even speed. Any recommendations?