Unmodded Slim Wont Play Purple Discs

I have an unmodded v12 slim that wont play any cd based PS2 games(purple discs) It will play all others perfectly including(DVD Movies , DVD Games , PS1 Games , Music CD,s). If it plays the older Ps1 Games which are CD based then why not ps2 CD Based ?? It's not the laser as I have Tested two other lasers in the machine and it does the same thing and all the lasers work perfectly in other consoles. Has anyone have any idea what might be wrong. ?????

Cheers

What behavior do you see when you try to load/run a PS2 CD?

When I put in a PS2 CD it comes up blue clouds then the "Playstation 2" screen appears , then it goes to black screen. The CD spins up fast as normal but screen remains black . The disc will slow down for a split second and then speed up again. This continues to happen over and over but black screen remains.
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