SCART-to-BNC RGB image weirdness...any help appreciated!

[kthulhu5000]

Hello, SHMUPS forum! I'm having a video issue that I'm hoping someone recognizes and can provide some assistance with.

I recently acquired a Sony PVM20M2MDU for RGB goodness, along with this SCART-to-BNC adapter off of Ebay. The adapter, obviously, is for adapting a SCART cable to attach to the BNC inputs on the monitor. All elementary to you all, I'm sure. And something that shouldn't be peril fraught. After all, there's no signal conversion going on, the PVM accepts straight RGB, and the SCART cables I have work just fine with one of those cheapo "SCART-to-component" video boxes.

First things first, I don't think the PVM is at fault here, and I'll explain why later.

Second, the cables I'm using. For my SNES, I'm using one of those cheap SNES SCART cables from Play-Asia. For my Genesis, I'm using this cable from the Retrogamingcables folks. That's the US site; I ordered mine from the UK one.

OK, here's the issue, when using my cables with the SCART-to-BNC adapter linked above...

The picture is steady, colors are there. With the Genesis cable, though, white seems to be missing. The most notable example is Sonic 1; when the game starts, there's normally a white screen with the blue Sega logo. In my situation, the logo is still there and still blue, but the screen is all black around it. The Sonic logo looks kind of normal, except all the white elements are replaced with black. I'll try to get a picture later.

So I tried my SNES cable, and it seems to be the same situation. Maybe even worse, though! Click the link below to see my crappy cellphone pic:

http://i.imgur.com/E75p22W.jpg

Basically, a hell of a lot of red, it looks like. Notably, no white or yellow, either; that Pokey or whatever is more orange, as are the letters in the game logo that would normally be yellow.

This doesn't appear to be a PVM issue. I have an Extron 7SC scaler/switch, which uses BNC inputs and passes RGB signals through. I actually tried this SCART-to-BNC adapter on it prior to getting the PVM and had the exact same problem with the SNES cable that I'm having now (using my LCD display). That image I linked? It's from my Extron test, but it's practically the exact same thing on my PVM.

So it's not a display problem that I can see. Rather, it's a cabling problem. Has anyone experienced this before, or does anyone have any advice about what might be going on/how to fix this/what a good adapter and cable combo would be?

Apologies for the length, and any info would be greatly appreciated!

[BuckoA51]

Wiggle the cable quite a bit (no, I'm not kidding)..do the colours come back momentarily? If so, definitely a faulty breakout cable.

[PAPER/ARTILLERY]

I'm not the expert on these matters but could it be something to do with how the RGB signal is synced? I know sync on green sometimes gives a green tint so perhaps this is something similar. Where's Fudoh? I expect he'll know.

[kthulhu5000]

I ordered a BNC adapter cable from daskrabs (his thread), so we'll see how this all plays out when it arrives. If the problem still persists, it might be a SCART cabling issue. Which would be weird as hell, since my cables do work in a SCART-to-component transcoder.

But no point sweating about that until the new adapter arrives...

[kthulhu5000]

Update: I received the cable from daskrabs, and things are now working just dandy! So it looks like the previous SCART-to-BNC adapter I purchased is borked in some weird, dumb way.

All's well that ends well, though (especially since my adapter arrived in the nick of time, right before a snowstorm)!

[PAPER/ARTILLERY]

Glad you got it sorted out mate

[pixelperfect]

Hrm interesting, I bought the same cable (http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 1019249428) from the same seller around the same time and i'm having the same problem as you reported kthulhu5000, non-existent whites on my Genesis (MD1). And since I have an SCART->YUV box i can tell the MD->SCART (from RGC) cable is okay.

I'll ultimately follow the same course of action as kthulhu5000 and buy one from daskrabs if I must, but I'm wondering, after having opened both cables, if I should first try changing the grounding on the faulty SCART -> BNC cable to use pin 18 instead of 21 .. (the MD1 - > SCART cable is using 18). Could that be causing the problem?

[broken]

Yes, lack of grounds will result in all sorts of wackiness and video/audio problems.

I would run a wire from pin21 to pin 18 and then to pin 4 (audio ground). At a minimum, in my opinion, these 3 pins should be tied to ground.

[pixelperfect]

Yep that was it! Thanks broken and thanks kthulhu5000 for the accurate description of the problem. Gave me the confidence to open up both cables and try to fix it

So as I was wondering and broken confirmed, moving the grounding cable from pin 21 to 18 did the trick. Whites are back and both my PVMs look great :] Seems like the particular ebay seller we went through is using the chassis grounding and nothing more. I'll shoot him/her an email suggesting they ground 18 as well if they want to keep using 21 to hopefully prevent this problem for others.

edit: Forgot to mention pin 4 (audio) was already grounded at least.

[CrystalUnclear]

Thank you for posting this thread. I talked to the seller about this since I wanted to get an RGB21 scart to BNC from him and showed him this thread and he told me he'll interconnect all grounds (video and audio) and wire every single ground to the SCART connector

[antron]

I have one of these ebay SCART to BNC cable, and can confirm not all grounds are connected. If I unplug the audio from my PVM the video looses its ground and behaves as described by the OP.