Nintendo systems jittery picture on HDTV solution?

[GUTS]

Hi, I've searched all over and I really can't find any info on this. I have an older Hitachi rear projection HDTV which I run all my older systems through a Jrok RGB->component converter. I've played almost every system out there on this TV; all Sega systems, Turbo Duo, PC-FX, Neo Geo, 3D0, CD-I, etc. You name it and it works perfectly through any input. All except the NES, SNES, and N64.

The problem is that the Nintendo systems do this weird thing where they'll look fine and stable for a random amount of time, anywhere from a few seconds to a couple minutes, then the picture will jitter extremely fast by a few pixels, then lock back to normal after another random amount of time. This happens through RGB->component, S-video, composite AV, and even RF (last ditch effort I dug out the old RFU adapters and used those, still did it).

After googling this off and on for the last year, I've basically learned that older Nintendo systems alone use some stupid resolutions that many HDTVs just don't like. So my question is; is there any possible solution? Some device I can run them through first maybe? Or am I just going to have to bite the bullet and buy an old tube TV (not really an attractive idea due to limited space in my apartment)? I figured if anyone on earth would know, it would be someone on this board. Everywhere else this question is asked all anyone gets is a bunch of inane replies about using emulators instead.

Thank you for your time!