Fisher Studio-Standard Belt-drive Sem...

This Turntable is part of a Fisher Sterio stack system that I bought in 1984. It probably doesn't have 100 hrs of play time but when I tried to use the turntable now I find that it turns slow making the record drag so I ordered and got a new belt and when I put the new belt on the turn table it seems to bind and won't turn at all. When I take the belt off of the pully the platter turns freely? I put the old belt back on and the platter will turn but still turning too slow and makes the record sound terrible. Is there a chance that the set screw on the drive pully may be loose? I tried to use a 1/16 allen wrench on it to see if it was loose but I think it takes a 1/32 allen wrench? Any help or suggestions would be much appreciated.