If your PS2 fat reads blue and black discs, but won't read or is slow to read DVDs...and cleaning laser doesn't work.....DONT buy a new laser. Just do this in small increments
Laser Lens Cleaner for CD DVD CD-ROM XBOX Playstation with Cleaning Kit PS2 PS3 39612112375 | eBay
Sony PlayStation 2 (Play Station) Slim DVD Repair (PS2 PSX) Scratched Discs (Cleaning Scratched CD) - YouTube