Can't answer your question but there may be a problem with the fine adjustment knob. At the top of the shaft there is a "C" shaped clip, I can't remember it's name, that can come loose and ride up the shaft. If that happens, the fine adjustment knob will just spin and not raise or lower the motor. If this is the problem, as long as that clip isn't damaged, all you have to do is push it down until it clicks into place. If that's not the problem, I can't offer any other suggestions.