Unless you are at a tech level where you are at least confortable disassembling a computer (totally) and re-assembling it from memory, I recommend staying out of your PS2. Unless it is very broken, and you don't care about getting it fixed economically.

Many of the online instructions are for specific versions (they don't always mention that) and some parts can be very easily knocked out of adjustment. If you don't mark the adjustment point of certian parts before touching them, you can be assured it will never read another disc.

I am of the opinion they were specifically designed to be difficult to service.