trouble shooting motors

[ponch37300]

I'm trying to figure out how to tell which parts of a motor needs to be replaced when a tool stops working. For example a drill, if it stops working or just hums. Is there a way to tell if it's just brushes or armeture or field or all of them? I can test if the switch is good and power getting to motor but is there a way to tell what's bad if you have power? Signs or something to look for that one part is bad? Just trying to figure out how to order parts without spending money on parts I don't need. The armeture and fields are usually pretty expensive so don't want to just start ordering away. I have a pile of tools I just set aside when they stopped working and am attempting to fix as many as possible. So trying to learn some trouble shooting skills to make sure I'm getting the right parts.

Thanks for any advice you might be able to share on this, Scott

[ponch37300]

Does anyone have any tips on how to tell if the armeture or field are bad? How they look when they are bad? I have a couple of tools that aren't working and the switch is good and has power. So it is either the brushes or the armeture or field I think. Just wondering if there is a way to tell what is the problem, either by looks or testing? I know that if brushes are worn down or burnt but wondering about the field and armeture.

Thanks, Scott