enwood Chef KM201 Speed control?

This is the electronic control version not like the 700 series with the centrifugal contacts, I have tried to adjust the 2 long screws to no avail, and then the carbon washer on the end of the armature shaft flew to pieces, is the carbon washer designed to rub against the two contacts or is it just the proximity to the carbon washer that regulates the speed? And should I just replace the whole controller board if the adjust screws dont work, Ray Sydney Australia