Supergun with RGB Scart - Sync question

[MrTimscampi]

Hello everyone

So, I'm building a supergun (Haven't got enough dedicated space for a candy cab right now...) which I'd like to be the most compatible possible with everything.
I'm laying down a schematic in EAGLE to hopefully get a PCB made which I can put in a sweet home-made control panel.

It has the standard Jamma harness and will output picture and sound to a regular RGB Scart.
I've picked bits from a few schematics I found online and mine looks like this at the moment:


It's a bit of a mess as this is the first time I design a PCB or write a schematic...
I'm using an AD8073 from Analog Device to amplify the RGB signal coming from the Jamma harness. (It was on one of the schematics I used and it was the only one having a SCART output, so I took the entire circuit for SCART OUT off of it. It had Composite and S-Video, but I don't need that and it just adds extra cost and hassle.)
But I think what I've done is right. If you find any problems, please tell me.

So on to my question.
As you see, the sync from the Jamma harness is connected directly to the Sync pin on the Scart socket.
However, I found some info about the Jamma sync and Scart sync signals and they seem quite different:
Jamma Video sync: 0-3V AC swing, 0-5V DC bias
Composite sync: 0.3V AC, 0-2V DC bias

Now, I'm not used to working with video signal (It's my first time working on a circuit that complex.)
But I can see there is a major difference here.
However, I don't understand why the website labeled "Composite signal" when RGB Scart has nothing composite... Maybe because both H Sync and V Sync are in only one signal ?
Anyway, can I just connect the Jamma Sync and the Scart sync without anything in between ? I've read some people did that and haven't had any problems, but the difference seems so huge between the two signals.

Other than that, my supergun design is pretty much complete, I think. I just need to put down the controls.

Thank you for the help.

[milkkart]

you're right, SCART uses H+V composite sync on the composite video pin of the connector. i've got my supergun wired up with no circuitry between the TV and JAMMA board except for a couple of 1k resistors on red and green and a variable resistor on blue to reduce the voltages down closer to SCART levels (was using scavenged components to jerry rig it and i've been too lazy to improve it.) i've been using CPS2 and MVS boards with it on a sony kv-2982u trinitron with no problems. of course it might not be the same with your tv and since you're doing this properly you should probably do something about it.

http://www.assemblergames.com/forums/sh ... hp?t=32766"
someone with pretty much the same question in that thread, some pretty detailed discussion in it. the recommendation seems to be a 1k potentiometer with one end connected to jamma sync, the middle pin connected to scart sync and the other end connected to ground.

what kind of boards are you looking to use this with? some boards (older ones mostly i think) can have none standard sync signals which cause problems for some TVs not sure if that's an issue with RGB SCART though.
also if you're going to be using CPS2 and MVS boards or anything else with stereo line out id suggest adding some phono sockets wired to R and L audio (pins 1 and 3) to use the stereo sound.
btw you should have jamma speaker - going to scart pin 4 (ground) and speaker + going to pin 3 (left/mono audio).

good luck with your build.

[MrTimscampi]

Thank you for the answer
I was planning to have a 3.5mm stereo jack right next to my Jamma harness. (On the right side of my panel.) to connect stereo audio from the boards.

If you read my schematic, you can see that Speaker - is connected to ground. But from what I researched, some boards offer Stereo on the harness (Like some MVS boards.) and one of the channels is thus going to Speaker -.
There is a switch that allows you to either ground Speaker - and send Speaker + to both channels or send Speaker + to one side and Speaker - to the other.

Concerning the sync, 0.3v seems to be the average. If it works when directly connecting the Jamma Sync and the SCART sync, I wouldn't care much about older boards having different sync. I don't thing It'll be much different... (After all, Arcade operators already pay a lot for a new screen. It would be messed up to fry them with different sync sequences. (At least, that's how I see it.)
I'll read the thread you linked and think a bit more about this issue, but I don't think it's that dangerous if it works on most TVs (Everyone I heard that did this seems to have no problem at all...)

As for boards I'm looking to own, I have an MVS (Model MV-1FS) coming my way as we speak. I also plan to get other systems like a Naomi and others and also older boards that are non-Jamma compatible (For which I'll make or buy an adapter.)

I'll be sure to post updates about the project
Again, if you have anything to correct in my schematic or modifications/additions you think might be useful for more compatibility.

[grobda]

I wired my test rig RGB straight to scart. sync to the comp vid/sync pin. its worked fine on 3 different tvs and 2 monitors over a period of about 10 years, all CRT's mind you.

only problem on TV's is overscan (IE picture too big), with inacessable adjustment. Also some TVs need to hook up the blanking pin, dont remember which one, fed it a line from the +5v and it worked, otherwise it was stuck in comp vid mode. (think thats covered on your schem..pin16?)

I put a 8ohm speaker in the enclosure for sound rather than hooking it up to the TVs speakers.

[MrTimscampi]

Yes, the blanking pin is covered. It actually takes +3v from what I've read. So I'm taking the +5v from the ATX power supply and I put a 220ohm resistor between the two to get the voltage down to the proper +3v required.
It seems that +5v is not a problem on the blanking pin, but for safety and to adhere to standard specs, I prefer to supply +3v instead of +5v. You never know, it might fry your next TV or one of your friends x)
I think I might go with the 1k potentiometer to allow me to adjust the sync for older boards. I don't want to buy a board and have the picture completely wrong afterward... Plus I've already got 3 potentiometers for the red, green and blue, so...

I'll finish the schematics and post it afterward. Same with the PCB design and gerber files. That way, if someone wants to use "my" design it's easier for them to get the board made.