on the back of the dial is a clock motor driven gearbox. inside this gearbox is a set of contacts which is a permissive for the m-wave to run (fan and lights also start). these contacts warps under long term use and won't close. BUT, the folks at sharp knew this and provided a peel-off cellophane window over the contacts where you can clean the contacts and bend them until they work again. how cool is that.