What goes bad in alternator?

[bgilbert]

So I'm working on my 74 gasser. It's not charging. Everything is pointing to the alternator being the culprit. New(er) battery, voltage regulator, ammeter wires tied together. Did the full field test and other tests in the book and still no more than 11.80 volts at the battery, with no charging . I've got the alternator off the engine and split in half on the bench. What goes bad and what do we (DIY'ers) replace inside them? All I can see that possibly looks out of the norm, is the windings inside what the book calls the stator, look to be discolored, gotten hot maybe, purple-ish in color...? So what goes bad?

[BC847]

Diodes and windings would be my guess.

[PToombs]

Diodes and brushes in my experience. Just spend the money and get a new or rebuilt one, then you know what you have to start with.
I could always tell when the diodes started to go. It would charge, but when you turned anything on, it would discharge more with more turned on. Since it doesn't do anything at all, I'd swap it out. JMO.

[BobS]

I fixed a lot of those when I did alternator repairs. Most of the time it was a worn out brush. They can be replaced without dismantling the alternator. Rarely was a rectifier. Regulator is external. The other thing was an open circuit in the rotor which could be fixed by splitting the rotor in half and unwinding a few turn off the bobbin coil and resoldering the lead back onto the slip ring. That was a PIA that I quit doing after doing only a few.