So both my Saturns stopped reading game discs. They both can read music CDs and most of the time they can even read the audio on game discs. On rare ocassions they will try to load the game, maybe even show the "Game licensed by SEGA" But then will remain stuck on a black screen.
Im afraid it'll probably has to do with the lasers, I haven't replaced neither since... ever (1995). Or maybe is the disc spindle distance? How can I narrow down the problem? (And solve it)
I don't have a multimeter and my soldering skills should be classified as "Highly dangerous to himself and others", so in case I need to adjust the laser lens, I'll go with the "turn a little and try".
If you're looking for a quick but temporary fix you can adjust the small trim pot on the disc drive. Mind you you should only turn it extremely slightly clockwise and then test again. This method will likely reduce the life of your lens in the long run.