PS1 (SCPH-5502) w/ mod chip color issue

Hi Guys,
I have an issue with my PS1, it is a PAL model SCPH-5502 with mod chip. I have not done the mod, it was done back in 1997 and it worked fine for years. I recently took it up, changed the CD drive that was not working and cleaned it a little. It is now displaying weird color banding (see attached image) when using NTSC games. The colors are right in the middle of the screen but off on the left and right sides.

Any idea of what is it? Is there a way to fix it?

Thanks a lot!
Alberto

 

Did you try the color mod to the CXA1645M chip?

 

Nope, I am a total noob in this kinda thing If you can address me somewhere where I can learn, it would be great!