RGB modded N64 - occasionally "stripy" picture

RGB modded N64 - occasionally striped picture

I did this RGB mod on my PAL N64 a while ago, and it works perfectly except for one thing; now and then the picture goes all "stripy", or whatever to call it. After a while the stripes starts to move more or less perpendicular to their direction, and then they disappear. I do however suspect that they're there constantly, just that they, so to say, move too fast to see when they're not visible.

This is how the signal travels from the N64 to the TV now:

The digital signal from the N64 goes in an unshielded ribbon cable to the DAC, which is built on a perfboard, and placed on CPU and GPU cooling flange. The output from the DAC then goes in four individual shielded coax cables to a DE-15 connector (VGA connector if you want) placed right above the original A/V connector. Then it goes through a modded VGA cable that I basically just put a scart connector on, each lead is individually shielded in those. The sync signal level is lowered to ~0,9v by a resistor, and the R, G and B signals are filtered by a 220 uF capacitor in the SCART connector.

My first thought was that some signal might bleed over somewhere, so I redid the cable and connections by the book, now the different picture related leads are individually shielded almost all the way, they're only "naked" a few millimeters here and there right at the solders at the DAC board and the different connectors. It might have helped a bit, but not much.

Then I tried different ways of grounding the shield. I've grounded them at the N64 side, the TV side, and both sides. No difference.

I also added 220 uF capacitors to the four leads to filter away low frequency noise, looking at cable diagrams for different consoles that seems to a common thing to do. Minimal to no difference.

I've been thinking about signal echo, but as far as I know the SCART connector's R, G, B, and sync connections are terminated internally in the TV, right? There should be no need to terminate the cable leads.

As you can see, I've had a very unscientific approach to this, just testing different tricks to try to improve the picture. None of them has really helped, so I thought it might be a good idea to really find out what the problem is instead of just continuing with the trial and error method.

This is a closeup from the intro screen of Zelda OoT on an occasion when the striping was quite extreme. The pixels on the TV are visible, and can be used as a size reference:




It might be worth to mention that the striping seems to be a lot less pronounciated if it appears when a static image is shown, for instance the ED64 menu, or if I just stand still in a game without touching the controls. Once I start to move, the striping becomes much more visible.

So, do anyone have any ideas at all what the problem might be? Perhaps a link to some documentation about troubleshooting this kind of stuff? Or maybe just some good search arguments for Google; English is not my mother tongue, and I don't know all the technical terms in said language, so I don't know if I've been using the right words so far