Problem with a SNES backup unit

[Vertigo]

Howdy.

I have what may be considered a problem with a Super Wildcard DX2 that I bought a while ago and has done this since purchase as new.

It was designated as NTSC version, though I think that's just because of what the bios outputs for video, than anything related to the use of it on my SNES, though it may have some bearing on what's going on. I'm using it on a PAL switched SNES and the problem is present in 50 and 60Hz modes. Always in RGB, and never present when I switch to composite.

What happens is that after a while the screen starts to vertically flicker, not roll like a sync issue, I can still see the whole picture, yet there is a sort of black vertical flickering overlaid on top, then after about 10 minutes it goes away, and returns intermittently. Like I say, this happens in 50 and 60Hz SNES modes, and I'm unsure exactly where the problem is.

I also have a US SNES but have been unable to test it on that as yet as I don't have an RGB cable for that, and there's no point testing in composite as the video is fine outside of RGB mode. I don't have S-Video. My TV supports RF, composite, PAL, NTSC and RGB. I desire to play in RGB only.

I don't like to use the unit on my TV when it's doing this problem as I'm sort of bothered there will be damage being done to the TV, but I'm unsure exactly what the problem seems to be. It's a very visible and irritating flicker, to the point where I pause and leave it until it's stopped. It's not electrical interference from any other outside source as I have used the same set-up in 2 different houses. Do you think a component in the unit or SNES is getting intermittently overheated and then cooling again, or could there just be a resistor that needs changing inside the unit itself? I have tried having a fan on it and the lid off and it still does it

Any other details, ask me.

Cheers.