2nd hand PS-One: artifacts on RGB output

[keropi]

Hello!

I purchased a 2nd hand modded PSone... but it's output has many artifacts... like RF noise in the background. I have tested 2 different scart cables and 2 TVs, one LCD and one CRT. It behaves exactly the same... Interference from other devices/signals is out of the question, as both sets have excellent quality with other console's rgb cables (ps2, saturn, snes, etc)

I have made a video so you can see , pay attention after the 15th second, where I zoom in an area: those are actually the artifacts the system has and not video compression ones...  

VID 00013-20100618-1838.3GP

is there something I can do to fix this?
thanks for any info!