Mcallister MRO1250 speed control?

Hello. I have a problem with the speed control. When it's on max speed it's perfectly fine. As soon as i take it off max it stops. Any speed apart from max it's dead. As soon as I click it back on to max it's fine. In assuming it's a faulty switch. Can I buy a replacement speed control and replace it. I'm fine using a soldering iron so that shouldn't be a problem.