Take the switch and exercise it. Flip it back and forth real fast about 20 times and maybe it will clean itself out. Not real hard but enough so it gets the idea to start working. This can usually get it going at least for a short time doing that and it is quick and easy to do. Some Deoxit cleaner will usually do wonders if the exercise helps. This is the first thing I do when I get an old radio that has been sitting for a long time. I flip and turn every selector as a matter of course.