My thermador gas stovetop has a downdraft fan. When you push a button at the back, a panel raises at behind the stovetop and you can then adjust the speed of the fan. The panel no longer raises when the button is pushed. I checked the voltage at the button and there is no voltage present. I checked the voltage at the terminal strip and it is good. There is a gear motor which is easy to acces and a gear motor switch which is a little harder to access. how can I check either the gear motor (windings?) or the switch. There is green corrosion on the GM switch connections but it is a small amount. If you could tell me how to check either one or what you suggest for troubleshooting, I would appreciate it. I have an electric meter to use for checking voltage or impedence.