I still have my PS2 and I decided to play some of my old favorite games. It only plays CD games, so it plays anything PS1 and some PS2 games such as Half-Life as they are CD games. The PS2 does not read DVD disks. I have already taken it apart, and was able to fix the CD voltage, but not the DVD voltage, and I don't remember it's original position. I have the slim PS2, and I've been turning it for the past several hours.
Looking at various FAQs and instructional guides, including IGN and GameFaqs, All of them said to start trying to find where the discs will read again by turning counter-clockwise by roughly 2 degrees each time up to about a 20 degree change. If that doesn't work, return to the starting position. (An easy way to keep track is to take some sort of marker, like a sharpie, and put a dot at the 12 o'clock position on the screw) If turning counter-clockwise didn't work, next was to go clockwise by 2 degrees at a time, up to roughly 20 degrees. If neither directions worked, next instruction was to repeat both directions, increasing the maximum, For instance, going up to 26 degrees instead of 20. Nowhere could I find a default degree. Just remember to go counter-clockwise first as that decreases the voltage and giving the laser too much may render it useless.