N64 S-Video Interference

[LaminGaming]

Over the past few years, I’ve been dealing with a peculiar issue when running S-Video from my PAL N64 through the Koryuu Transcoder. There seems to be some type of grounding issue that’s causing unwanted interference in the image (scrolling diagonal lines that show up prominently in primary colours) when the cable is fully connected to the Koryuu. As a workaround, I discovered that the interference goes away if you have the cable slightly disconnected, which works, but I was wondering if there was a permanent solution. Does anyone here know of a fix or what might be causing the interference?

Here’s an edit I made comparing the cable fully connected (on the left) and slightly disconnected (on the right).

[BuckoA51]

Which S-video cable are you using or doesn’t it make a difference?

[LaminGaming]

The one I used for the screenshots is this one by Retro Verse: https://videogameperfection.com/products/pal-n64-svideo/

It happens with every cable I’ve tried regardless of how well shielded it is, so it doesn’t seem to be an interference issue with the cables themselves, I think it’s probably got something to do with how the PAL N64 is outputting the signal or how the Koryuu is treating it. I don’t know if this issue happens with an NTSC N64. I also checked the composite output and that was okay, so it’s only the s-video output.

Here’s another edit this time showing composite on the left and s-video on the right. With the s-video you can clearly see the lines on the red and blue of Mario’s clothes.

[LaminGaming]

Thought to make another post after some further investigating. Still not sure what the issue is exactly, but I noticed that the interference seems to increase gradually whenever the Koryuu is turned back on after being turned off for a bit. It also seems to vary in how fast/slow the interference scrolls across the screen over time, even changing direction.

Thinking it was the power, I decided to check the PSU’s voltage output. It read 11V and 3.5V, which is close enough to 12V and 3.3V that the N64 needs, so nothing wrong there.

I even tested the cable on my SNES and had no issues, so it can’t be the cable. The interference is most likely inherent to the N64 internally, I just don’t know what’s causing it. Since the interference mitigates when the cable is slightly disconnected, it makes me think it’s the grounding, maybe a ground loop. Admittedly, I don’t know much about ground loops, but I read a post a while ago from someone else who thought the same thing.

This post: https://videogameperfection.com/forums/topic/koryuu-s-video-interference/page/3/#post-42287

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