Originally Posted by
TheAbysmalDark
This is probably not a lot of help but the usual cause of disc read problems, as for other consoles, is a laser issue. Either the positioning or a dirty lens.
I have no PS2 laser experience only with the original Xbox laser and most problems with that are indeed down to a dirty lens. YT videos suggest this is true fro the PS2 as well.
Sometimes a very small pot tweak does work for the Xbox. Problem with that is you need to know how to do this precisely or it can end up significantly reducing the life of the laser or end up not reading any disc types. Pot tweaking should be considered the last resort.
The fact that one or both of your new PS2 laser assemblies is scratching the underside of PS1 discs suggests a fundamental problem with its positioning. Whether this is caused by the replacement laser's design or your re-assembly would be guess work.
What type of PS2 are you using 'fat' or 'slim'? Are you 100% certain the laser assembly is designed for your particular PS2 model? If you're not sure check. I've found evidence that state that there are regional differences which some online sellers warn about :-
"This replacement FULL optical block is made of a brand new PVR802 lens for PStwo only (V12) and also includes the full optical block around it. CAREFUL: On some PS2 (mostly in Australia), there is another type of lens, which is wider, code name: 3170SPU, which is not compatible with the PVR802. Open your console to make sure which lens you have."
Several also state (maybe just for sales reasons) that you need to use a full replacement optical block ie. cradle, worm drive and disc spindle/motor designed for the new laser, not just the very much cheaper laser assembly itself.