Strange problem with NESRGB and Insurrection RGB SCART cable

[otj]

I just completed an NESRGB 2.0 install in a top loader belonging to a friend of mine, and I'm experiencing a very strange issue with it that has me stumped.

If I use SNES s-video cables or the HD Retrovision SNES cables, it seems to work fine, albeit with some diagonal noise in the s-video output. The major problem comes up when I try to use an Insurrection Industries RGB SCART cable wired for c-sync. The cable works fine with my Voultar board and marqs dejitter board equipped 1-chip 01 SNES, but if I attempt to use it with the NESRGB multiout, I get loud buzzing from the audio and the video output is mostly red and gray.



The install is using the Voultar NESRGB QSB FFC Kit and a rear multiout panel from Laser Bear Industries. I'm very happy with the cleanliness of the installation, and I don't think I goofed anything up, but maybe?



Lastly, I hauled out my scope and hooked it up to the SCART cable to see what in the world was going on. This is a white screen in the 240p test suite, and as you can probably tell, that doesn't exactly look like a white screen... Not sure what this output indicates, but I know it's definitely not right.



Any ideas? Did I perhaps mistakenly assume I could use any SNES SCART cable wired for c-sync? I'm really hoping nothing was damaged.

[otj]

So it looks like I didn't goof anything up. I measured directly at both the multiout and the NESRGB, and it's perfectly fine.
I guess the question now becomes what is it about that SHART cable that's causing it to throw a fit... Hmm.

[viletim]

It's probably a got a broken ground connection.

[otj]

It's probably a got a broken ground connection.

After taking a quick look, I think that's the problem. I get the sneaking feeling that the issue is this, or something similar: https://twitter.com/voultar/status/1356362963247132672

I have noticed that only pin 5 on the multiout kit I installed is connected to ground on the board, but not pin 6. It should be both, right?

I suspect the SCART cable has ground connecting to pin 6 only, which is why I get no continuity between ground on the NESRGB and the SCART head. I'll have to confirm this tomorrow, but I'm 90% sure that's it.

[viletim]

Both pins 5 and 6 of a multi-av port need to be connected to ground. Sometimes a cable connects only one pin, and you never know which one it's going to be.

[thebigcheese]

Possibly related, but I know that my NES just generally has audio buzz when using cables that aren't fully individually shielded. I have to use a big, thick Retro Access cable to get clean audio. And yes, on my multiout, pins 5 and 6 are wired together on the PCB itself.

[otj]

And yes, on my multiout, pins 5 and 6 are wired together on the PCB itself.

Are you using the Voultar FFC multiout?

Both pins 5 and 6 of a multi-av port need to be connected to ground. Sometimes a cable connects only one pin, and you never know which one it's going to be.

I've confirmed that's exactly what's going on. On the multiout, only pin 5 is connected to ground, and on the cable only pin 6 is connected to ground. D'oh!

Either I damaged the multiout PCB somehow, or there's a small design issue there. I doubt I can fix the cable seeing the connection is made in the sealed multiout connector, but maybe I can link the grounds on the multiout PCB...

[thebigcheese]

And yes, on my multiout, pins 5 and 6 are wired together on the PCB itself.

Are you using the Voultar FFC multiout?

No, I bought this years and years ago. I can't remember where I bought it from, but there's a trace connecting the two pads so they are definitely wired together. Regardless, I still needed the Retro Access cable to get rid of the buzz. AFAIK, Insurrection Industries cables are not individually shielded, so if connecting the pads doesn't fix it, you might also need to look into a new cable.