symptoms of worn brushes

[chippy mark]

I was using my circular saw today when it started to make a strange noise it sounded a bit like spluttering and some sparking was coming from the motor, other than that it is working ok.
Is this the first symptom of worn brushes or does it sound more serious?

 

[doorframe]

If you're lucky it's worn or stuck brushes, or possibly a dirty commutator, but you'll need to investigate to see.

If none of these then you're unlucky and it's (almost certainly) the armature windings, in which case find a nice big bin.

Sorry.

Roy