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Thread: Jamma to Scart question.

  1. #1
    drunk downunder!
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    Jamma to Scart question.

    I'm currently working on building a CMVS and I've stumbled across a Teac SCART CRT. I have no idea if it will accept RGB though as there isnt an owners manual and the service manual doesn't tell me the specification of the SCART socket. Unfortunately I do not have any scart devices so I cannot test anything.
    Checked the OSD Menu, lets me change between PAL, AUTO and NTSC for colour system, not much else though. the SCART is only on AV1. AV2 and AV3 are composite with S-video being a seperate channel (S-VHS).

    The above is now unrelated as I have a working Loewe CRT with RGB scart.



    I've found this page which is making a JAMMA -> SCART adaptor look pretty easy but I'm wondering if I'm missing something here.

    http://www.gameland.gr/geoanas/realarcade.htm#scart

    For testing purposes I'm interested if the simple diagram on above url would be sufficient.

    I've heard of adding a 100ohm resistor to the +5v to reduce that down to 2-3v. Not sure if this is needed or not as its not listed on that page. Also heard about adding 75ohm resistors to the R,G,B signals coming from the JAMMA before the SCART socket. Also not sure on that one.

    Audio I wont be bothering with as I will use the CMVS headphone sockets.

    Any help will be appreciated.
    Last edited by lachlan; 01-23-2011 at 07:02 AM.


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  2. #2
    Geese's Thug

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    It should take RGB, it's part of the SCART spec. Only really shitty knock off chinese tv's i've seen dont accept rgb.



    Just follow that.

    Put a 100ohm resistor on pin 16 of the scart, this will bring the 5v down to the 1-3v spec.

    The RGB and SYNC lines will probaly need resistors on them. Older CRT's tend to look fine but some will have really bright colours.

    Try it without first, if its too bright put some resistos in there, start about 220ohm for each.

    If you run a +12v to pin 12 on the SCART socket the TV will automatically switch to the SCART chanel when you turn the MVS on.

  3. #3
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    Quote Originally Posted by jew90
    If you run a +12v to pin 12 on the SCART socket the TV will automatically switch to the SCART chanel when you turn the MVS on.
    Well, it should. Many TV's I've come across haven't actually had this "feature".

  4. #4
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    Quote Originally Posted by Hewitson View Post
    Well, it should. Many TV's I've come across haven't actually had this "feature".
    That sucks!

    It is part of the SCART standard so TV's should follow it, but then again i've seen TV's where only the primary socket is capable of RGB and the others have had non-standard wiring like SVIDEO / Component.

    So it's no surprise.

    So, it might autoswitch depending on TV. Mine does (14" Sony CRT from late 80's early 90's)

  5. #5
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    I have gone through this process and now have a working cmvs on a 14" Philips CRT.
    I have just been given a fairly new (relatively speaking) 21" Sony Trinitron, and although the picture is nice and clear it has a green tinge.

    I have read about it before (And I know PS2/PS3 consoles have issue with DVD Playback) I am sure it has something to do with RGB Sync being sent, does anyone know a way to resolve this?


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  6. #6
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    The PS2/PS3 outputting a 'Green' screen when playing DVD's over RGB was done as a form of 'copy prevention' which Sony said.

    I presume this was to stop decent quality VHS copies being made from a good RGB source? *shrug*

    I think you can output DVD fine as Y/Pb/Pr Component.

    Did you put Potentiometers onto your RGB lines like I mentioned before?

    If one color is stronger than the other you need to increase the resistance in the line to balance it, this is different on different TV's, which is why POTS are a great option. 1K is what I used.

    In the NeoGeo bios menu, under hardware test you get a color pallete to calibrate the monitor with.

    This can be used to calibrate your RGB pots.

    The Sync line sounds fine as you have a picture.

    On my 14" CRT all my pots are in the same place, on my friends LCD I have to have the blue up more than the green and the red down slightly to make the picture look good.

  7. #7
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    Quote Originally Posted by jew90 View Post
    Did you put Potentiometers onto your RGB lines like I mentioned before?

    If one color is stronger than the other you need to increase the resistance in the line to balance it, this is different on different TV's, which is why POTS are a great option. 1K is what I used.

    In the NeoGeo bios menu, under hardware test you get a color pallete to calibrate the monitor with.

    This can be used to calibrate your RGB pots.
    I did on another one when I was trying to use it on an LCD and it made no difference.
    I thought they were used to reduce the brightness levels through each colour and as it was working on another CRT I didn;t even look into that. I thought it maybe a TV issue.

    I will try that tonight, I will also look at the BIOS and see if that helps.
    Thanks for the info.


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    The pots on the RGB lines will adjust the intensity of each color individually.

    Since the NeoGeo MVS doesn't output TV standard RGB not all TV's will display a proper picture. Many will be too bright.

    If you have a green tinge this is a sign that the intensity of the Green signal is too much, if you had a pot on there you could turn the green level down.

    The color check menu in the bios will show you four coloured squares, red green blue white.

    With this on the screen you can turn your RGB pots up and down until the image is as it should be, exactly the same way you would adjust an arcade monitor. :-)

    If you can't adjust the colours with RGB pots satifactoy then i'd look else where, but since this is a common problem RGB pots are the first thing to try.

  9. #9
    drunk downunder!
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    So basically as follows.

    Red to Red (Pin 15)
    Green to Green (Pin 11)
    Blue to Blue (Pin 7)
    Sync to Comp Video Input (Pin 20)
    Speaker - to Audio Ground (Pin 4)
    Speaker + to Audio Input A (Pin 6)
    Ground to Common Ground (Pin 21), Red Ground (Pin 13), Green Ground (Pin 9), Blue Ground (Pin 5) and Blanking Ground (Pin 18)
    5v+ to Blanking (Pin 16) With 100ohm resistor between the JAMMA and the SCART. I made the mistake of getting some 180ohm resistors, I'm guessing this is too high?

    If the colours are too bright or intense I'm supposed to add some 220ohm resistors to each of the RGB lines or some 1K pots?

    I've stripped a SCART cable and kept the above lines. As long as I wire it up as so it should work.

    In regards to a SCART CRT, I've recently found a Loewe CRT that will satisfy my needs.


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    Quote Originally Posted by lachlan View Post
    Speaker - to Audio Ground (Pin 4)
    No, that couldn't be more wrong. Do this:

    Jamma L to Scart 6
    Jamma 10 to Scart 2
    GND to Scart 4

    This way you'll have dual mono with Jamma boards and stereo with MVS multislots.

    Quote Originally Posted by lachlan View Post
    5v+ to Blanking (Pin 16) With 100ohm resistor between the JAMMA and the SCART. I made the mistake of getting some 180ohm resistors, I'm guessing this is too high?
    You want voltage to be in the 1-3V range. Use this formula to choose the resistor (R):

    R = (Vin/Vout * 75) - 75

    Vin depends on whether you use 5v or 12v. Vout is the voltage you want at the scart blanking pin, let's say 1.5V or 2V.

    As you see 180ohm is just fine.

    Quote Originally Posted by lachlan View Post
    If the colours are too bright or intense I'm supposed to add some 220ohm resistors to each of the RGB lines or some 1K pots?
    470ohm pots are enough.
    Last edited by MKL; 01-22-2011 at 09:08 AM.

  11. #11
    drunk downunder!
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    Thanks MKL, looks like I'll have Stereo with my MV-2F.

    I see what you mean with that formula, won't forget this one. I'll update here later once I've wired it up to the JAMMA.

    470ohm pots on the RGB lines to adjust, 180ohm resistor on the 5v+ line.


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  12. #12
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    It's very important to remember that in most cases a PCB has an amplifier which is of a push-pull type. Speaker - is not ground, it is the opposite of speaker +.

  13. #13
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    Quote Originally Posted by Hewitson View Post
    It's very important to remember that in most cases a PCB has an amplifier which is of a push-pull type. Speaker - is not ground, it is the opposite of speaker +.
    I was following that guide above, good to know it isn't correct or I would've wired it up like that. Cheers.

    I find it odd that the Video Ground from the JAMMA isnt connected to the scart somehow but I suppose it's just there to create a circuit, nothing different from the GND on the JAMMA edge?


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  14. #14
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    That is strange, actually. Although most boards would work fine with that configuration, the video ground should be used for the RGBS grounds.

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    The only reason I can think of for not using the video ground for the RGBS grounds is to make the wiring simpler. I can't find any other JAMMA to SCART solutions to compare this with however. Maybe I haven't looked hard enough.


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  16. #16
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    I tihnk its quite obvious whoever made that diagram didn't have a clue.. There is certain games that won't work with the ground wired that way. JAMMA provides a video ground for a reason.

  17. #17
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    The ground pins on the jamma connector are all the same. They're just supposed to make the wiring easier/tidier.

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    I have heard reports of certain PCB's not displaying a picture unless wired to video ground. Better to play it safe and do things properly I reckon.

  19. #19
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    I tend to not believe people's disgnoses. Sometimes they're really convinced of the most absurd things. Check this out:

    http://www.neo-geo.com/forums/showpo...1&postcount=12

  20. #20
    drunk downunder!
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    Well considering it's only for an MVS I'll take the tidier route but obviously for anyone using scart for a supergun, video ground would be proper.

    I'm using a male to male scart cable, on this site http://geocities.ws/podernixie/htpc/...tml#jammascart it has a note saying the following.

    "Note: if you use a standard male-male scart cable and a female socket you must change the following pins: 20 → 19, 6 → 3 and 2 → 1. This is because a male-male cable connects inputs to outputs."

    Is this true? I wouldve thought that they'd mirror each other on both ends?


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  21. #21
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    Yes, if you put a female scart on a supergun/CMVS it will be an output connector and scart cables use different pins for audio and composite inputs and outputs. On a standard male-to-male scart cable pin 19 at one end goes to pin 20 at the other end, etc.

  22. #22
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    Think of it like a null modem or crossover ethernet cable.

  23. #23
    drunk downunder!
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    Quote Originally Posted by MKL View Post
    Yes, if you put a female scart on a supergun/CMVS it will be an output connector and scart cables use different pins for audio and composite inputs and outputs. On a standard male-to-male scart cable pin 19 at one end goes to pin 20 at the other end, etc.
    Alright so If I cut one end off the male to male cable and wire that end to individual RCA's I'm assuming that this does not apply?
    Last edited by lachlan; 01-23-2011 at 06:59 AM.


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  24. #24
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    You can use whatever custom connectors you want at the end that plugs into the supergun as long as the male scart that plugs into the TV uses pin 20 for composite (sync) and pins 2 and 6 for audio.

  25. #25
    Geese's Thug

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    I use a 6 pin DIN socket on my supergun as it takes up less space. RCA's you have a chance of mixing up, your going to need a few of them.

    This has enough pins for the SCART cable. Use an 8 pin DIN if you want audio.

    I don't run audio to the TV but have a built in mini-speaker on the supergun. However, unless you add some attenuation then your feeding amplified sound into the TV which is bad for the TV's amplifier (especially if the PCB is turned up)

    Anyhow.

    6 PIN Din

    1 - 5v
    2 - 12v
    3 - CSYNC
    4 - RED
    5 - GREEN
    6 - BLUE
    Outercase - Ground

    This then goes to a SCART plug the other end.

    The +5v goes via 100ohm to enable RGB mode and the 12v feeds directly to the auto-switch/status pin.

    This puts the TV on the correct AV input and at 4:3 when I turn the supergun on.

    You can of course use a female scart plug (bulkier / bigger).

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