You have to follow the 2 sets of wires and unplug from the circuit board.  To remove the turn knob, the pointers show which screws to remove . On the lower right screw remove the ground wire that connects to the plug on the small circuit board and unplug the plug. Then gently guide the wires through the opening while pulling out the turn knob from the other side.

Once the turn knob is out turn it over like the picture to the left and you will see 3 screws. You will need a long narrow phillips screwdriver for these. While unscrewing these hold the knob in your hand so the cover doesn't fall off. Now turn it back over and remove the top cover.

Now this is what it will look like. For this part you need a small phillips screwdriver to remove the rest of the screws. Remove the screw that holds the 2 ground wires. Then remove the screw that holds the spring. Gently lift the spring up were you just removed the screw to release the pressure. Now lift the turn section of the knob straight up guiding the ground wires through the center.

Now you will see this. Remove the screw holding in the micro switch. (NOTE: This screw is longer than the other 2 you took out in the previous step so don't mix them up.) Then you remove the plastic cover piece and the red thumb button. slide up the micro switch and put a couple drops of rubbing alcohol on the button. Push button to work it in and get rid of any build up around the button. Also be a good time to check to make sure there is a good connection to the wires. Now just reverse what you did to but it back together.

When putting the turn knob back on you will need to make sure you line it up properly.  The 2 blue pointers line up the center gear with the 2 center holes. And the 2 red pointers line up with the 2 outer guides with the 2 outer groves.

When you put the turn knob back in. It will only go in one way. There is a groove on the bottom of the shaft that lines up with the dimple that the pointer is showing. Also make sure you guide the wires back through carefully and reattach to the circuit boards.

Then turn your machine on and test it. Hopefully it works as good as new.