How to make a NTSC PSX backup work in PAL PS2?

Hi from Spain,

I've got a PAL PS2 with modchip. So far it boots PAL & NTSC PS2 backups, but I've only been able to boot PAL PSX backups and not NTSC ones. I've in fact tried to boot an ORIGINAL NTSC game (Lunar 2 USA) unsuccessfully. I've read I must make a backup of it using patch-it to pass it to PAL. I did it and the resulting backup doesn't boot in my PS2, it just freezes in the "Sony EUROPE" with the Playstation logo screen. However it actually boots in my modchipped PAL PSX, also mentioning "EUROPE" in that screen, so I guess it's actually patched, but it just doesn't work in my PS2.
Any help will be welcome.

Thanks.