Why many PSX games doesn´t run on my PS2???

[XXCrashXX2]

Hi i have a PS2 V7 with Magic 3

Ps2 Games no problems all games run

but PSX Games only a couple of games run.

This the games the are not running : Resident Evil all parts
Theme Hospital, Risiko.

Have anyone an idea.

I used a Pioneer A05 and Clonecd for Copys but no copy works.
has anyone an idea???

Thanks for all answers.

cu