Ignoramus15926 wrote:



What I do not understand is how could only one brush burn out?

Any idea?
If the copper braid pigtail develops a bad connection, then the thin spring
has to carry the current, and it will get annealed in a second.

The braid is supposed to be buried deep into the carbon before it is pressed
and sintered. Sometimes they cheat on material, and only a mm of braid is
inside the carbon. Or, the braid could get fatigued, corroded or not be
soldered well to the spring retainer/current contact piece. Any of these
will fry the spring, and often the whole plastic brush holder assembly.

Jon