Author Topic: Anyone here knowledgeable in RGB -> Scart hacks? (Read 2694 times)

Nipedley · « **on:** January 14, 2006, 12:33:55 pm »

Heya guys, I thought I'd have a go at wiring up my machine to a television - and well, the cable is complete but I get no picture. I'm not sure why, anyone have an idea?
I have the following wired up (in order of the picture);

Red -> Red
Green -> Green
Blue -> Blue
White (Ground) -> Frame Ground, Red Blue + Green Ground
Black (Sync) -> Comp. Video IN

When I turn it on, I just get a blank screen on A/V.. Though there is some kind of signal getting through, because the bar that has channel information starts flashing red. Any help?

Nipedley · « **Reply #1 on:** January 14, 2006, 01:58:31 pm »

Hrm... case solved..? I found that one of the wires left disconnected was the Comp. Video ground wire, now the plans I used didnt list this as one that required connecting but sense tells me that if the sync is being used through Comp. Video in, it would need to have the ground connected too. Thoughts?

Orclord · « **Reply #2 on:** January 14, 2006, 04:37:04 pm »

What plans did you use ?

I saw quite a few different ones when I done it...

I had to take +5v to scart pin 16 ( blanking) to get it to work on my Grundig, although I think there should be a resistor in there to knock it down a bit, and other people have not needed the +5v at all

Nipedley · « **Reply #3 on:** January 14, 2006, 05:36:47 pm »

Thank you =)
Can you remember if you needed to hook up the composite video ground? I should think so, but the plan's I looked at said not. For the record, they are the only ones I could find - Videogames on Alternative Monitors FAQ by Jonathan Dawes

Orclord · « **Reply #4 on:** January 15, 2006, 04:01:34 am »

As far as I can remeber I hooked all grounds up..

Here's a Few more sites..With differing versions...

http://www.mameworld.net/dosmame/advanced.php

http://www.nexusuk.org/projects/vga2scart/

http://www.idiots.org.uk/vga_rgb_scart/

Nipedley · « **Reply #5 on:** January 15, 2006, 05:51:18 am »

Thanks for the sites, I now have all my rgb, ground, and sync wires connected but I still get nothing. It almost looks as if the tv doesnt know what to do with the signal, which seems odd. Did you get a picture before you connected your blanking pin? I don't see what could be wrong, other than that

Orclord · « **Reply #6 on:** January 15, 2006, 06:23:06 am »

No I had a blank screen.......

Andy at Ultimarc used a scart hack and his works without anything to the blanking pin, so do a few others I seem to recall...

Have look here http://www.acl.co.uk/pinouts.htm scroll down and you will see for pin 16 it says 1-3v for RGB.....

It might be the others were just throwing a composite and not an RGB signal to the TV.....

By the way my TV was a Toshiba .....Now it's a Grundig...

*Edit*

Oh yea and That's where I should have used a resistor to drop the voltage to 3v, But I was lazy and just wanted to see if it would work...I would advise you use a resistor, I don't want to get the blame if things go tits up..

Nipedley · « **Reply #7 on:** January 15, 2006, 07:01:09 am »

Ah thanks =D I'll give that a shot, any idea what size resistor is needed? I have a bunch, but I know little about them. Also, is it safe to take the 5v from the machine's power supply? It'll be lovely to actually play my machine for the first time since September!

ADD: Going through the links you gave me, it seems like I need a 100 ohm resistor - and from my electronics kit thats Brown-Black-Brown? Could anyone verify that before I end up melting my television? Thankies =)

Orclord · « **Reply #8 on:** January 15, 2006, 07:20:12 am »

100 Ohm I *Think*....

Yea should be no prob from the machines supply....I took mine from the Midi/Gameport...

Yep it is 100...have a look at the scart control signal section on the idiots.org link I posted...You can kill 2 birds with 1 stone using just one connector..

Nipedley · « **Reply #9 on:** January 15, 2006, 07:57:51 am »

Success.... kinda, looks like I got no sync - but the pictures tharr!
The sync goes to Comp. Video IN right?

See attatched pic.. or if you want to watch the vid (that was just a screen cap), its 2mb:

Any ideasss..?

Orclord · « **Reply #10 on:** January 15, 2006, 08:07:51 am »

You should have the H+V sync from the vga cable twisted together and going to pin 20 on the scart....

What Videocard are you using and what Frontend..?

Nipedley · « **Reply #11 on:** January 15, 2006, 08:09:37 am »

I have negative composite sync, as for my videocard and frontend - im using my arcade machine. Wanted to have a play while my monitor's are out

It's going to Pin 20, and it's the right type of sync since its Jamma and all this is is a Jamma -> Scart adapter.. Methinks loose wires perhaps, I will go check

Orclord · « **Reply #12 on:** January 15, 2006, 08:19:57 am »

Ahhh I see.....

Jamma--->Scart....

Never done that.....

*Runs away*

Nipedley · « **Reply #13 on:** January 15, 2006, 08:24:56 am »

Ehehe, well if you ever want to try gimme a call

Thanks for your help buddy, I'll get around to re-wiring the sync soonishly.. Hopefully I can get this thing working soon

Orclord · « **Reply #14 on:** January 15, 2006, 08:32:27 am »

No prob..

I hope you get it going...

ZeroPoint · « **Reply #15 on:** January 15, 2006, 08:52:14 am »

What graphics card are you using ?

Are you sure you are using correct 15Khz timings !?

Nipedley · « **Reply #16 on:** January 15, 2006, 09:26:25 am »

Quote from: Nipedley on January 15, 2006, 08:09:37 am

I have negative composite sync, as for my videocard and frontend - im using my arcade machine. Wanted to have a play while my monitor's are out

Ahem

Nipedley · « **Reply #17 on:** January 16, 2006, 02:37:55 pm »

hmm... well, I re-wired it all today - and still no luck. The only thing left I can think of, is disconnecting the composite video ground (guide didnt say to connect it) and the function select pin.. all my ground connections are good etc. as I checked em all. Other than those two, any other ideas?

Orclord · « **Reply #18 on:** January 16, 2006, 05:34:48 pm »

Not too sure at all...

You could try a full +5v to the blanking for a short time just to see if that makes any difference, but I doubt it...

Or you could just have a TV that refuses to lock onto the Jamma signal.

Not alot of adjustments you can do on a TV unless you can get into service mode, and in there you can make a right royal cock up.

Have you got another TV handy different make just to see if you get the same result ?

As you can see I'm pissing in the wind, beacuse as I said I have never tried it..

*Edit*

Just another thought did you ground the blanking signal...Pin 18 ?

Mr-Megalo · « **Reply #19 on:** January 16, 2006, 05:52:10 pm »

try sync on pin 19 instead of 20

Mr-Megalo · « **Reply #20 on:** January 16, 2006, 06:13:03 pm »

just opened up my supergun scart lead, sync IS pin 20

i'll get mi coat

Nipedley · « **Reply #21 on:** January 16, 2006, 07:10:47 pm »

I'll see if I can get another tv out there tomorrow, and thanks for checking mr megalo.. any chance you could see for me if the comp. video ground is connected? The guide said not, but sense says yes o.O

ADD: Forgot to mention, blanking ground is also connected - I know if blanking isnt connected, as I get no picture at all

ADD2: At first I thought one of my grounds was fritzy because not only was the signal from the machine all out-of-sync but any other channel I went to was the same - however I checked em all today and they are all good - frame ground, rgb ground, comp video ground and blanking ground.. right?

Mr-Megalo · « **Reply #22 on:** January 16, 2006, 09:12:59 pm »

no probs I'll check it in the morning - I'm a bit more drunk now than I was afew hours agao

Silver · « **Reply #23 on:** January 16, 2006, 11:30:21 pm »

Not quite sure where you are at so apologies if I repeat anything.

You will definately need at least 8 wires hooked up in the scart:

Red
Red Ground
Blue
Blue Ground
Green
Green Ground
Sync (composite in its probably labelled, pin 20 as you say)
Sync ground (18 for composite in, if memory serves.

If jamma does not give you independant syncs (ie just R,G,B,Sync,Video Ground) then you will need to split the Video ground to all the above grounds. Every signal must have a ground.

This is just the signal. Scart has standards, but different tv's often try a "best guess" and will detect an RGB or a composite input. Some won't.

Also, some tv's with scart sockets will NOT take in RGB. They will only use the signal on the composite pin. I'm not familiar with jamma, so not sure what you get. If the tv only takes composite, or needs the correct scart signalling to switch to RGB (can you select the input type on remote?), then you would only see a black screen even if everything is wired correctly (you would be watching the syncs).

Again, just trying to cover the basics so sorry if you've got all that sorted.

Nipedley · « **Reply #24 on:** January 17, 2006, 01:11:27 am »

Yep I got that... managed to get the picture displayed after a bit of messing around, and it certainly looks like it takes RGB since it actually displays the picture. It just rolls everywhere and is very liney and messy and well.. out of sync

elvis · « **Reply #25 on:** January 17, 2006, 01:34:26 am »

Just a question - what gameboard are you using to test with? And does your TV have hsync and vsync trimpots on it? In the days of old when we hooked up obscure non-TV things to TVs we often had to play around with the sync fine tuning on the TV to stop the picture rolling.

Nipedley · « **Reply #26 on:** January 17, 2006, 01:35:31 am »

Wouldn't know, its still inside the case and there's nothing on the front. Not going to take it apart for such a small project, and for the record its a Megatech gameboard

elvis · « **Reply #27 on:** January 17, 2006, 01:48:11 am »

From what I can see the megatech games are all locked at 60Hz exactly. Is the TV in question NTSC compitable? I see by your location that you are in the UK, which could mean your TV might be PAL-only (ie: locked to 50Hz).

Sorry to ask such obvious questions, but I'm just trying to fill in the blanks.

Nipedley · « **Reply #28 on:** January 17, 2006, 02:06:30 am »

I believe it is, yes. It's a relatively new television, and it's a sanyo. I don't really have any way to test it right now though :/

Orclord · « **Reply #29 on:** January 17, 2006, 03:15:24 am »

And also if your TV has more than one scart socket, you must connect to AV1. That is the only one that is RGB compatable.

I would think your TV would be NTSC capable being a newish TV, my Tosh was and that was years old.

Nipedley · « **Reply #30 on:** January 17, 2006, 10:40:57 am »

It only has the one.. it must be an RGB socket though, or I wouldn't be seeing anything at all would I?

elvis · « **Reply #31 on:** January 17, 2006, 08:54:17 pm »

Quote from: Nipedley on January 17, 2006, 10:40:57 am

It only has the one.. it must be an RGB socket though, or I wouldn't be seeing anything at all would I?

Correct. The composite uses a YUV type encoding, so the colours would be missing, or no picture at all. You've got all your colours which makes it look like the pciture signal is getting through, just that the sync is either wrong, or missing all together.

Just wondering... perhaps your board is sending negative sync where the TV expects positive, or vice versa? Do you have any documentation on the board and it's output? Not that I have any idea at all how to convert one to the other mind you.

Nipedley · « **Reply #32 on:** January 18, 2006, 01:11:20 am »

The sync signal is just a "standard" jamma type sync signal, negative and composite. I guess my only real option is to try swapping out the tv's - I'll give that a go later. I'll let you know how it goes, thanks for all the help guys


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