Anyone knows how the speed control of the Kenwood Chef works?

My Kenwood Chef suffers from very low power. I took it apart and tried to understand how the speed control system works. The speed control nob moves a plate up to increase the speed. I couldn't figure it out! I will check the capacitors and the resistors, but I have no idea if this will solve the problem. Any rocket scientists around to explain it to a simple soul?

Attie
August 2009