What's wrong when PS2's stop reading CD (blue) disks ?

[mud ver.2]

I've heard about some PS2's being unable to boot original CD based games, but boot original DVD games fine.

What would cause that ? Seems strange.

[dust2dust]

not that strange at all
1 laser lens is used for both but many other parts that produces diff beams to either dvd or cd
it happens all the time

try cleaning with a cleaning disk with brushes on it normally does the trick although dvd are normaly first to fail

try adjusting the lasers cd pot ,there seperate pot for dvd(get a pro to do this

if still no good then it looks like the laser needs replacing

[mud ver.2]

Thanks for the reply dust.

It's not actually my console doing this. I was checking out the broken ps2's on ebay. lol:D