Major Knight at Mojave is the first guy. If you are friends with the BOS Paladin Sato will fix it when he's at the safehouse, which is once or twice a week. Raul will also fix it, but I think there may be some bugs with that. There's other people that fix things, but I think those are the big 3 that can fully repair anything.
the guy at 188 trading post who is at the food stand right next to where veronica is, also the female ghoul scientist assistant at jacobstown repairs stuff, also lady gibson etc.