My buddy has an original Donkey Kong cabinet, has had it for years and one day the monitor was like this when turned on. Recap, flyback, both? I don't believe the monitor has been swapped so all the electronics are original to the cabinet. Any advice would be much appreciated.
The Screen knob on the flyback is turned on way too high, that's why you're seeing those lines. Use a plastic tool and turn it down until you no longer see them. Hopefully its just that, if you can't dial in an acceptable brightness and colors after adjusting the screen I'd look into recapping or something else going on