I've bragged about the Electrolux MagicMill Assistant many times before. Its a work horse. It makes my KitchenAid Pro look like a scrawny Freshman trying to do a pull up. But it does have some minor flaws. One is that there is no on/off switch, rather there is a timer that turns it on and off. The problem is that if you want to stop the machine before the time runs out you need to manually turn the timer off. Not a problem except that it loosens and ultimately detaches the knob.
Well, I finally had to disassemble mine to fix it, so here is a pictorial on fixing this problem.
UNPLUG YOUR MACHINE
Notice the knob on the left turned past the off label. In fact, I could turn the knob back and forth a full inch or more before anything happened, and in the end the knob was clearly not attached to anything. I had assumed that I had broken the spring, so it was time to crack it open.
Start by pulling both knobs straight out - be careful to not torque them to the side - straight out. Then, if your nuts and washers are still in place remove them and remember how they attach.
Take a butter knife and pry from the side seam. Note that the bottom will pop out first. There are three flexible arms with catch triggers on the end on the bottom edge, while the top has three anchor points that will disengage once the bottom is off.
We can now see that it is a very simple mechanism inside. Be careful to not loosen any wires. The knob holder peg will stick out and just off to a side is a small pin. When the pin is in place the mechanism will sit at roughly 20º so don't expect it to sit horizontal to the machine.
See the little peg 2mm to the left of the knob holder?
Return the mechanism to its place, lock in the knob holder with a washer and nut. Be sure its tight and that the mechanism is no longer moving. Return the face plate by settling the three top anchors into their slots. Then snap the three flexible arms on the bottom into their slot. Double check your knob holder, and if its stable, return the knobs to their holders and give it a try.