If it is bearings you should be able to feel them when you spin the shaft by hand. It will be stiff and you would probably find some spots harder to turn past than others. If it is the switch you should see some sawdust drop out of it when you tap lightly on the side around the switch. This was a problem some Bosch routers had until the factory replaced them with one that wouldn't clog up.(Bosch sent them to all customers who had that model free of charge by the way.) Brushes have to be inspected to diagnose easily. Check the power cord while you're at it. If you get the router running lay it on its side and wiggle the cord around. If it runs normally when you get it running it likely is something simple.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.