Audi 5000S Quattro not charging

[Lokkju]

Hey all, hoping some one can give me a suggestion here...

I have a 1987 Audi 500S Quattro, and it has been throwing it's
alternator belt about once every couple months (the star type thing on
the bolt that tightens the alternator is a bit stripped, so I have
been trying to get it to stay in place by torque alone).  Anyway, I
was driving home last night when my battery light started to blink,
telling me that it was dying - I figured oh well, I'll change the belt
(since that is what has always happened in the past).  But after
getting it home, and taking a peek, the alternator belt is still on
there, and tightly enough that it seems to be turning the alternator. 
Before replacing the alternator, is there anything else I should
check?

Thanks