Custom SCART cable questions - AC Coupling, Grounding etc

[slikvik]

I have a few questions around custom SCART cables for various retro systems.

Do most SCART cables need AC coupling caps on the RGB lines? I know the Mega Drive ones need 220uf for example but I've heard the PS2 has the caps built into the system, so wondered if that was common for other retro systems?

Same question for the 75ohm resistors. Again the MD cable has these on the RGB lines but do some systems have those built in too?

Do all the ground pins on a SCART connector need to be wired?

Can the ground pins come from one conductor, or should you really keep them separate along the cable (assuming you have more than one ground conductor in your multi-core cable? Given you only have one ground from the console side usually, it doesn't seem like it would make a difference?

Any reason the coupling caps can't be wired at the console end of the cable instead of the SCART end? (Apart from ease of fit)

[BazookaBen]

I can't give you good answers on most of those questions, but I can say that there is probably some misinformation out there muddling things up.

Like I think it was RetroRGB that said Sega Saturn needs a resistor + cap on the sync line in the SCART head, even though the R,G,B lines do not. Insurrection Industries, maybe because of what they read from RetroRGB, included these components in the SCART cable I bought from them a few years back.

I had unusable picture with those cables until I removed both the resistor and cap, then it worked well on all my CRT setups. And I tested this on four different Saturns

So I'm wondering if there was something wrong with Bob's Sega Saturn, or if it was some odd revision that didn't include correct attenuation like the four I have

Any reason the coupling caps can't be wired at the console end of the cable instead of the SCART end? (Apart from ease of fit)

From what I've read, it would actually be better if you did. I think the closer to the source of the signal, the better. Less chances of reflections. So if you were going to make custom RGB cables, you'd want a little box a couple inches away from the connector to house all the caps and resistors. Sort of like what a lot of cables house their ferrite chokes in.

[slikvik]

From what I've read, it would actually be better if you did. I think the closer to the source of the signal, the better. Less chances of reflections. So if you were going to make custom RGB cables, you'd want a little box a couple inches away from the connector to house all the caps and resistors. Sort of like what a lot of cables house their ferrite chokes in.

This was my understanding too, thanks.

Annoying about the discrepancies around decoupling cap and resistor values from various designers of SCART schematics. For some rarer systems (like the Amstrad CPC) the "de-facto" schematics for SCART show no decoupling caps or resistors but I suspect this is more to do with fact that they're designed by people many years ago, who don't really know enough to design a proper SCART cable compatible with the system.