Flickering mega tech screens

[Arrrhalomynn]

I finally found someone to buy my spare sega mega tech. I dusted it off a bit and fixed some stuff. After some messing around I noticed that both screens flicker a bit, but when I remove one of the monitors (pull out the rgb cable) the flickering stops). It doesn't matter which screen I unplug.
Does anybody know how I can make both screens flicker-free and working at the same time?

[Arrrhalomynn]

Somebody? Anybody? (befores this goes to the next page).