It's a known trick on Sega Saturns too. I had to do it to mine. Changing the potentiometers increases the laser strength, which a) shortens the life of the laser (but hey, if it's not working anyway what've you got to lose!?) and b) sends a higher intensity laser beam which reflects better because it's stronger, so the receptor picks up the data better.
Eventually, though, all the lasers will be put up to max power and still not work, then it's new-laser-time.....
Edit: Incidentally, I've not tried this but in theory this should allow the drive to read CD-RWs too, if you up the voltage enough....
