This like new powerful 1/2” Milwaukee 5380-21 corded hammer drill rarely will turn on. When it does, it seems full power. 120volt ac is ALWAYS measured on both sides of both brushes when switch is depressed, but only rarely will it run. It’s completely dead, no click, no hum, no heat, no smoke! Brushes look smooth and almost new. Armature appears smooth, but I have not dismantled. I’m convinced the switch is OK. What’s my problem?