Saturn SCART problem

[zyrobs]

After seeing the terrible quality of the play-asia RGB cables, I decided to do a direct SCART output onto my Saturn, removing that 10-pin bastard connector and soldering the output directly to the motherboard. Currently, I have a small ribbon cable inside the machine, that carries video output from the Saturn motherboard into an internal USB connector I removed from a spare PC motherboard - it was the only small enough connector I could find with enough pins. (soldering directly to the motherboard would be a permanent solution, which I why I did this)

This shebang is connected to the SCART output, wired up according to this diagram:



... except for pin 8 (aspect ratio control) which I omitted, and the audio/composite input/output pins switched around, as I attached a female connector while the diagram is for a male one. (just exchange pins 2, 6, 20 with 1, 3, 19). Ground pin is daisy chained.

Now, the problem is, I have this wobbly washout ontop on the picture, most visible on yellow background (ex. Virtua Fighter Kids title screen). It's the exact same problem I had with the play-asia rgb cable. I figure this happens because the scart connector takes h/v sync info from the composite video signal, and the extra video data causes interference. Now, the Saturn outputs composite sync on a separate cable, and sure enough, using that in place of composite video removes the washout entirely.

However, if I use pure sync, the picture is jumping up and down! Like, randomly once or twice every second. How should I go about fixing this? What could be the cause? The cables I use are all well shielded and high quality, so that can't be the problem...

For the time being, I've connected both c-sync and composite video to the same pin, this reduced the washout effect significantly, but it's still annoying enough.

Moreover, if I switch from 50hz to 60hz, the washout effect is removed. (I've yet to try c-sync only with 60hz output). This is only a partial fix because I have quite a few PAL games which are optimized for 50hz, so I'd like to have 50hz too.

[NFG]

I get the jumping around problem when I use my NeoGeo on my TEAC CRT TV.  It seems to be a result of the display being a little uncomfortable with the sync rate.  Basically, a modern display choking on the retro demands.  Not sure if this is your problem as well, but the problem sounds exactly familiar.

[zyrobs]

Well, it's true that I'm trying to get it working with a 2009 Viera.

Also, another minor problem: whenever the screen gets bright, the audio becomes noisy. I'd assume that this is because brighter picture = higher amperage on the rgb pins = more interference to the audio... but, if I disconnect the 5v pin to force composite, there is no audio noise at all, even though the rgb pins are still connected. Could be something in my TV, or I need to add some resistors to the rgb pins.
It's easy enough to fix though, I'll just add direct rca audio output. Or maybe the optical mod, once I get an amp that has optical input. (it can be done without touching the DAC chip, since the 4 required data/clock pins have connectors on the motherboard)

[NFG]

The Saturn has notoriously bad audio, and a ground loop results in a hum that gets louder when the screen is mostly white.  I get the same thing, which is why I use my HiSaturn Navi more often than I probably should (it has a separate headphone port with no hum).

[zyrobs]

Yeah, but I only get the hum in RGB mode. Never in composite. Also, on the play-asia cable, there was only one ground pin and it still had audio noise (but not in composite).

[zyrobs]

Okay, I took some measurements. C-Sync signal was 1.74v, which I guess is out of spec because adding a spare 300ohm resistor made the picture stable (with the resistor in, c-sync signal dropped to 0.51v)... except that now hi-res mosaics show rainbowing. I combined composite and c-sync into one line and put the 300ohm resistor onto that, and now the picture is pretty damn good in both pal and ntsc modes. Now I'll just have to deal with the noisy audio. Not sure how could I add RCA out and keeping the internal connectors - I doubt another cable would fit into that end...



Out of interest, what is the voltage spec for c-sync in scart? 0.75v? How much resistance would I need to have that exact voltage?