Help with making SCART to BNC cable for PVM.

[dreadnought]

I can't solder to save my life, and so have to either buy cables or find somebody who makes them. Recently I needed some for a PVM and managed to buy a ready made VGA-5xBNC (works fine with my MiSTer), but couldn't see any female EURO to BNC ones in my neck of the woods (I'm in Poland). There are some for sale in the UK but with taxes and shipping it'd be quite an expense.

Eventually I found an auction locally which was selling a similar (but not quite) PVM-dedicated cable, and the seller said he also makes custom ones. I asked him to make one for me so I could plug my machines which usually connect via Euro SCART to my assorted TVs, into this PVM. He did, but it's not working - the image is rolling heavily. The cable is female SCART socket to 4 BNC (RGB+ Hsync - I think).

The guy is an older geezer who knows nothing about micros or TVs, he just makes cables. I'd like to get him to either correct this cable or make a new one, but now I need some concrete blueprint to feed him. Do you know where I could find a schematic for such cable, or maybe have some ideas as to why the one he made is not working? PVM is Olympus OEV 203, it's got two banks of Component/RGB inputs. The cable uses 50 Ohm threads instead of 75, but I think I read somewhere thsi should be ok?

[Guspaz]

There's no hsync with SCART. You need red, green, blue, and composite video. The problem is that SCART is unidirectional, so composite video could either mean pin 19 (composite video output) or pin 20 (composite video input) depending on the direction.

I'd use a multimeter to check which pin is connected, and then have him swap it to the other one.

[dreadnought]

Ahhh...I see, so it's all about csync. It's my fault then, since I asked him for HSync based on me thinking of that VGA - BNC cable. Though if there's no HSync why did he solder it at all (I had a look inside the plug it seems to be soldered to pins 16 & 14)...

Could you elaborate a bit on the "I'd use a multimeter to check which pin is connected, and then have him swap it to the other one." thing? Or, perhaps, de-elaborate since as you can see I'm completely clueless. I'm just not sure how to explain the whole "unidirectional" thing since I don't quite grasp it myself and he doesn't speak English. Isn't there just one unified diagram for this sort of cable I could show him?

[Guspaz]

Pin 16 is the blanking signal and pin 14 is the ground for data, dunno why he would solder to those. Are you sure you're counting right?

SCART doesn't have a concept of csync. Composite video is normally carried on pins 19 or 20, and RGB uses that for sync.

[dreadnought]

Thank you for replying. But, is there really no consistent way to tell which pin to use for composite video? Is it not constant? I mean, I can't tell him to measure anything since he's not connecting to any console or PVM, he just makes these cables. Also, the cables which are for sale, eg this one, must use one or the other - they don't mention anything about there being variations?

[Fudoh]

he probably mixed up the input and output pins for composite video.

If you want the cable to act as an adapter from FEMALE Scart to BNC, then the sync line needs to connect to pin 20.

RGB pins are bidirectional, so they're the same, no matter which direction your cable has.

So, pins 7+9+11 (RGB), pin 20 (sync/video), pin 17 (video ground) and possibly some more ground lines are the minimum to create a working adapter cable.

[MarkOZLAD]

The RGB grounds are designed to be used with the cable shields.

[dreadnought]

If you want the cable to act as an adapter from FEMALE Scart to BNC, then the sync line needs to connect to pin 20.
[...]
So, pins 7+9+11 (RGB), pin 20 (sync/video), pin 17 (video ground) and possibly some more ground lines are the minimum to create a working adapter cable.

Yes, it's supposed to be a female adapter. Thanks a lot for the concrete info, I will pass it on and hopefully it'll be ok this time.

Though now I realised I should probably ask for the sound to be pulled from the SCART as well, right (like in that cable I linked to)? Or can I just connect to the audio out on the PVM itself?

[Fudoh]

easiest way is certainly to connect two RCA breakout wires next to the BNC ones.

Like sync audio is unidirectional, so pay attention to using the right pins.

[fidde_se]

Dreadnought if you need to buy any let me know, I'll make them on a regulary basis and I'm just across the pond from you, Sweden that is.

[dreadnought]

What do you think of this cable with "sync stripper"? It looks similar to the cheaper cable, and the site says it "A composite sync signal eradicates timing problems often experienced with old gaming machines.". What does that mean exactly? That some consoles might not sync with some PVMs?

@fidde_se: thank mate, wish I knew earlier. I will see how it goes with my guy here first, maybe will give you a shout later. Do you have a website, or some sort of online presence?

[Guspaz]

Never use a sync stripper unless the device that you're connecting to requires clean csync. Few devices do. Extron switchers are a notable example.

[fidde_se]

@fidde_se: thank mate, wish I knew earlier. I will see how it goes with my guy here first, maybe will give you a shout later. Do you have a website, or some sort of online presence?[/quote]



I'm a little everywhere, some at eBay, some at VGP, the one in question can be seen here
https://www.tradera.com/item/170704/529 ... or-pvm-bvm

[dreadnought]

Alright, the saga continues...

I gave the cable back for corrections and the man did it, but it's still not working. The image is now stable, not rolling, so perhaps the sync is okay. The image in RGB mode is very faint and ghosted though, nearly invisible. When I choose COMP-INT in the PVM menu the image is okay, but is all green.

He told me then that this is how it's all connected:

5 - blue (-)
7 - blue (+)
9 - green (-)
11 - green (+)
13 - red (-)
15 - red (+)
17 - sync(-)
20 - sync(+) with 1kOhm

Does it look okay to you? He also pointed out that the earlier "RGB on 7+9+11" (suggested here) does not comply with the SCART standard - perhaps it was a typo from Fudoh?

About that 1kOhm on pin 20, that was put there on my request - I had an idea that since the signal is supposed to be coming mostly from MiSTer, there is a resistor needed? I wanted a 470 Ohm one, as per the standard MiSter advice, but he didn't have it at the time and put that 1k there. Do you think this could be causing problems (ie, there should be no resistor at all, or if, then exactly the 470 Ohm one?).

[Fudoh]

sorry about the RGB typo. It's correct on your current layout.

1 kohm on the sync line won't work. On a PVM you don't need the attenuation anyway. So either remove it, or replace it for a matching one. If go higher than 470 ohm you're decreasing the sync voltage to a level where it's probably no longer useable.

[dreadnought]

So I eventually got that cable made. It works...kind of.

-MiSTer connected via DAC HDMI-VGA dongle + UMSA VGA-SCART + this cable: image is ok, but there is a slight noise interference. Not sure why because the same setup, only using common SCART-SCART cable from UMSA works fine on my consumer TVs.
-PAL Megadrive, modded to work with NTSC and using standard DIN-SCART cable + this cable - image somewhat stable but heavily ghosted and colours off (this one works fine on my consumer Trinitron with DIN cable)
-Japanese Dreamcast - via standard SCART cable + this cable - image is out of sync/ scramble (this one works fine on my consumer Trinitron using SCART cable)
-ZX Spectrum +2 - via DIN-SCART cable + this cable - works ok.
-Japanese Saturn - via SCART cable + this cable - works ok.

So it's a mixed bag really, can't see any pattern here. Any ideas why some of these machines refuse to display properly?

For anybody interested inb buidling one here's a pretty good write up: https://strefapsx.pl/forum/strefa-obraz ... -stripper/
It's in Polish but it should be easy to translate / self explanatory, plus there are good photos all round.