Hello Rob and welcome!
Interesting, that. In my experience of using MOF177s and DW625s there are normally only three things which go wrong - brushes, bearings and (sometimes) speed controllers. What state are the brushes in? These can sometimes be an issue - I've even had cracked ones where tools have been dropped, but not that common. When powered off does the router turn freely by hand or does it stick? If it doesn't turn freely then suspect the bearings. What was it that caused you to suspect the speed controller? Sorry for all the questios, but I'm trying to come up with a solution
"Unfortunately there is lots of bad information online; some of it is really scary. It's probably not intentional, but I've seen some content that sets up the illusion that you can do whatever you want and get away with it" - Norm Abram in an interview with Jefferson Kolle