backup psx won't work on PS2v4

[longlegs]

I've got loads of psx backups pal which work fine on my psx but won't load on my ps2 neo2.2.
I've adjusted the laser pot with some success.
Some of the titles have had the PSX loading screen altered, can this be the reason.
Also I have patched some NTSC titles to PAL and used Gamester for the pal region, work great on PSX but no joy on PS2.