Most likely there is NOTHING wrong with the speed control board. You have a dirty one. When you get to step 4, pivot the board out without disconnecting anything. Remove the 4 screws that attach the plastic cover to the board and CAREFULLY remove the plastic cover. Get a spray can of contact cleaner and spray the hell out of the slider slot and the black microswitch above it. Go to town on them, particularly the switch nub on the bottom of the microswitch. put the slider to full speed and the knob to full speed and reattach the plastic cover to the board. Check to see it slides freely and clicks like it should. Reassemble the mixer and enjoy its function. The reason these fail is crud gets in the slider and switch. Contact cleaner fixes them both for less than $20 a can!