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RGB problems with consolized NeoGeo MV1c

Discussion in 'Arcade and Supergun' started by erkan, Sep 7, 2013.

  1. erkan

    erkan Spirited Member

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    Hi,

    I have some problems with a Neo Geo MV1-C that I have consolized.

    The RGB cable I built does not work 100%. It shows normal startup graphics output when I turn on the MVS on my Sony CRT but when the horisontal and vertical bars shows up (if I do not have a game inserted) the screen goes black as if the display is lost. The same thing happes if I boot with a game inserted. Its like the display output is dropped once the game is supposed to run.

    But when I run the MVS on my Sony flat screen TV instead then the display is never lost! Instead I get a rolling image of the game so the game is running and there is display output all the time but it is not stable, looks like a f"n sinus scroller from an Amiga demo.

    I tripple checked my RGB cable and it is based on this one: http://www.neo-geo.com/forums/showthread.php?220333-Jamma-to-Scart-question

    I tried taking ground from pin 14 and pin 2 and there is no difference.

    On my SCART-plug I got, red, green, blue, sync, 5v, left channel and right channel (did not bother with audio ground before picture is working), ground is connected to pin 5,9,13,18.

    I put a 100ohm resistor on red/green/blue and sync and put a 100ohm resistor also on pin 16.

    I assume something is wrong with the sync line, but what can be wrong? Do I need another resistor or something?

    Maybe the MV1-C is broken, however I can see the game running on my Flat screen so I assume it is something I have missed on the cable.
     
  2. retro

    retro Administrator Staff Member

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    Sounds like the way your television deals with no signal.

    Regarding resistors, use whatever value brings the appropriate line to the right value within Péritel spec. And I wouldn't use fixed resistors on the RGB lines - use pots if you want to use something.

    Why haven't you wired pin 8?
     
  3. erkan

    erkan Spirited Member

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    There is a signal, on my flat screeen I can see the game but the screen is rolling. On my CRT it just goes black after boot when the game should be showing. Is the signal too strong perhaps?

    Do you think the fixed resistors is the reason image disapears? Same thing happened before I added the 100 ohm resistors to RGBS-lines. My first cable did only use a single 100ohm resistor on the 5v line.

    As I understood it, if you feed 12v to pin 8 your TV auto switches to 4:3 mode, since my TV is already 4:3 I assumed I did not need it. My MV1C runs on 5v only so I do not have 12v. Also, I can just press a button on the TV and it goes to AV1 witch is RGB.
    Do you need to have 12v on pin 8?

    Thanks!
     
    Last edited: Sep 7, 2013
  4. sanni

    sanni Enthusiastic Member

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    Putting a 100 Ohm resistor into the sync line really doesn't sound right.
     
  5. retro

    retro Administrator Staff Member

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    Sorry, I slightly misread your original post - I thought the issue was only when no cart was inserted, not during gameplay as well.

    If the cable works on one display but not another, it's your display that's doing it. It could be that it's more sensitive on the switching.

    Fixed resistors could cause problems if they're wrong, but I wouldn't think they'd completely lose image, no... and especially as you had the same without them in place. You should try without first, then add pots if the colour needs attenuation.

    Pin 8 is a function switch, sometimes the RGB switch. Some televisions require it. Pin 16 needs 1-3V if you're running RGB mode. I wouldn't wire it direct to +5V as per that diagram. And don't take other people's values for granted - test it. 100 ohms should be OK if you're using +5V, though.

    A rolling picture could be a sync issue, but it might be fixed with a tweak of the vertical hold on your television, if it has one. Why did you put a resistor on the sync?

    Oh, and you will want to connect audio ground. And I'd connect to common ground on the SCART, and check all grounds on the JAMMA end are common, tie them if not.
     
  6. Bad_Ad84

    Bad_Ad84 Keyboard Error: Press F1 to Continue

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    Doesnt the MVS output a slightly off sync signal anyway?

    Rings a bell, which could explain why one tv works and another doesnt
     
  7. synrgy87

    synrgy87 Well Known Member

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    removed earlier post due to incorrect info, while i don't think i needed them for all displays, i do have resistors on the Red(75ohm) Green(75ohm) Blue(75 ohm) and SYNC(75ohm) lines and pins 8 and 16 hooked up to +5v via a resistor(180ohm), all the grounds hooked up to common ground. which gives me a nice stable picture on both 1994 sony trinitron CRT and my acer LCD monitor / TV, also on my JVC CRT and via a GBS-8220 converter to a VGA display.

    I double checked this as it was bugging me :) hope that helps, 100ohm on the sync line might just be too much for the sony TV

    le video of said cable setup working on the sony tv: (this is on my faulty MVS 4 slot)

    [video=youtube_share;dGnLF-33AQs]http://youtu.be/dGnLF-33AQs[/video]

    hope this helps
     
    Last edited: Sep 7, 2013
  8. retro

    retro Administrator Staff Member

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    I'd certainly try without the sync and double check the voltage on pin 16 and try pin 8 ;)

    Bad_Ad, could be right, yeah. I seem to remember seeing something odd with the sync in a Neo Geo RGB cable many moons ago.
     
  9. erkan

    erkan Spirited Member

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    Thanks for suggestions! :encouragement:

    I will try sync without 100ohm resistor, let you know how it went.
     
  10. Bad_Ad84

    Bad_Ad84 Keyboard Error: Press F1 to Continue

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    http://www.jamma-nation-x.com/jammax/cmvs1fs.html

     
  11. erkan

    erkan Spirited Member

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    Ok, tried sync line without 100ohm resistor. The only difference was that the picture was more stable on the flat screen but the screen was still wavy and a bit shaky, unplayable. Same behavior as before on the CRT.

    I am kind of burned out on this project now, can you for example buy a PS2 RGB-cable and just wire up the right wires from the MV1-C to a female PS2 video connector and use that cable?

    Or is there any site that can build a SCART to DB9 cable for an MVS system?

    Thanks!

    Ah.. many thanks, maybe I will try it later in the fall, I will let you know how it went off course.
     
    Last edited: Sep 7, 2013
  12. Calpis

    Calpis Champion of the Forum

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    *head explodes*

    Remove the resistors. Don't use pots! They're a cheap hack and will hurt signal integrity and change color characteristics. The NG's sync frequency is fine, if your display doesn't sync to it it's because of the cheap analog circuit used (or system damage), and this can be fixed with a better sync driver. Don't add a capacitor ANYWHERE on sync, it will only make things worse. Do NOT wire the NG's 5V to the display if that's what you mean (!!!).

    MVS like most arcade systems do not output TV level signals; the only way to properly "consolize" the system is to use voltage dividers to attenuate the RGB signals, put them through a video amplifier (internal level shifting), and series terminate the output with a 68/75 ohm resistor depending on whether the amplifier has a little output resistance. My suggestion is to copy the Neo AES's output circuit, but replace the encoder chip with a dedicated video amplifier chip.
     
  13. kuze

    kuze Peppy Member

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    Are you saying that one can't simply tap rgb and sync from an MVS board and feed that (along with 5v and ground) to a TV without an amplifier circuit? I'm working on a 2 slot cmvs currently and haven't had much luck so far getting my framemeister to accept the signals.
     
  14. synrgy87

    synrgy87 Well Known Member

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    you can do that, as the video i posted shows, but i've never tried it on a framemeister.

    PAL tv sets with SCART will accept the R G B and S from a MVS and many other arcade PCBs directly or with little else added(Provided the SCART socket is an RGB enabled one). As said 75ohm resistors on the R G B and S lines worked for me on multiple TVs and devices. but some will be more sensitive than others. +5v going to pin 8 with a resistor of 180ohm going to pin 16 and all the grounds hooked up. should work fine, no video encoder needed. separate video encoder circuit only needed if you're going to go to S-Video or Composite video from the RGBS.

    from the OP's profile saying "Sweden" and his post saying "Sony CRT" i assume he has a RGB SCART enabled CRT TV and is just losing sync and/ or something isn't grounded right. or the 100ohm resistor on the sync line is too much

    but then again i could be completely wrong :)

    4,5,9,13,17,18 and 21 should be grounded
     
    Last edited: Sep 7, 2013
  15. Calpis

    Calpis Champion of the Forum

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    You can try, but you cannot expect it to work reasonably well or at all, and it is certainly not the correct way to proceed. Signals out of the MVS (and most arcade boards) are vastly different to what TVs are designed and calibrated to accept. Most people use potentiometers to attenuate the signals to a working level, and that may be acceptable to them, but truthfully it affects the signal's integrity severely and the only reason it works/appears to work at all is because the display is very forgiving and compensates for the mangled signal. The only correct way is to use an amplifier. It doesn't have to be an IC amplifier specifically for video, although that would yield the best results. You could instead use just a common-collector amp, but then you have to design a good attenuation/level shift frontend (1 transistor and 5 resistors per color component at its most basic design).

    DO NOT CONNECT 5V FROM THE NEO GEO (OR ANY CONSOLE) TO A DISPLAY'S 5V LINE, EVER. GND YES, 5V NO!
     
  16. synrgy87

    synrgy87 Well Known Member

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    why not? the 5V is for the RGB/mode select/switch

    Edit: for the record i think i get what you mean, i'd source the +5v from the power supply not just a random point on the board?

    another note the instructions on jamma x are for component output and not for RGB SCART.
     
    Last edited: Sep 7, 2013
  17. kuze

    kuze Peppy Member

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    Forgive my ignorance, but where would you suggest pulling 5v from instead?
     
  18. Calpis

    Calpis Champion of the Forum

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    I thought SCART provided a power rail and that was what you guys were wiring 5V to, which would cause a low impedance path from ~5V rail to ~5V rail and possibly lots of smoke... The mode pins are obviously not that, but even still connecting 5V like that is perverse and doesn't seem like it could be the proper usage of the pin. My guess (I don't live in a SCART country and it's barely documented online), is that the TV pulls the pin up to 9-12V/whatever through a resistor, and you're supposed to set the mode with another resistor to GND, creating a voltage divider.
     
  19. TriMesh

    TriMesh Site Supporter 2013-2016

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    It is the correct usage of the pin - the basic idea is that it's used to detect if an external device is both connected and turned on, so it has to rely on an external voltage source to do that.
     
  20. erkan

    erkan Spirited Member

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    Interesting. So you should get a separate 5v power supply for the SCART pin?

    Can you buy some kind of premade video amplifier that converts RGB to RCA or super video for example (and runs on 5v, hopefully it will be safe to use 5v from NeoGeo on this?). I would rather have a system that works with all displays than just some specific TVs.

    It sounds easy saying to clone video amplifier of NeoGeo AES but then my MVS will be playable in 2050 (if it works at all).
     

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