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Thread: Sync level adjustement for PCB

  1. #1
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    Sync level adjustement for PCB

    Hi,

    Just grabbed a small LCD TV with analog RGB input (scart).
    I have tried several boards and obtained different results (MVS, ST-V, KI, CPS1)
    Refresh rate probably differs from one board to another, however is there a way to adjust the sync level by adding a dedicated device or a pot on the sync line?
    The whole idea is to get rid of the Framemeister for arcade+supergun.
    No, I do not have a PVM/BVM.

    Note: KI works great as it is. MVS being the most affected.

    Thanks,

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    what is the problem exactly? It is a little unclear to me. When you say refresh rate, do you mean flicker or vertical hold issues?
    If using a PAL TV you may have issues with 50/60hz sync signals.

    if using SCART you need to make the PCB Sync into 1vp-p, not 5V TTL coming from JAMMA conn.

    "boosting" the Sync is not usually necessary, it is TTL already (logic high or low). However, JROK sells a great little sync cleaner that fixes issues with messy sync from some PCBs. However, it doesn't sound like thats your problem (MVS has very clean sync).

    if you *must* amplify your sync / adjust it, Extron made a nice sync box you can find on ebay probably.

    -Segasonicfan
    Last edited by segasonicfan; 12-28-2016 at 03:34 AM.

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    You could always run whatever PCB through an Extron RGB or similar device. These input/output devices condition the sync along with RGB so that they're acceptable to a wide range of displays. I personally use an Extron RGB 160xi but thats more for conditioning before the PVM so I don't need resistors.



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    will Extrons fix PAL / NTSC issues though? I would love to get something that takes 50hz in and puts out 60hz (RGB). my old extron stuff wouldn't do it.

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    No I don't believe so, that said Extron has a lot of hardware models to choose from. I would not be surprised if they have something that would help.



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    Quote Originally Posted by segasonicfan View Post
    will Extrons fix PAL / NTSC issues though? I would love to get something that takes 50hz in and puts out 60hz (RGB). my old extron stuff wouldn't do it.
    You will get terrible screen tearing and/or jerky scrolling doing that. Better to have a display that natively supports 50hz.
    Last edited by Yodd; 12-28-2016 at 07:32 PM.
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    how come? Ive always wanted to know more about that conversion process.

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    Well, I don't know the science behind it, but every device I have tried that forced it (GBS boards, XPC-4) or allowed to control it (Framemeister) always resulted in pretty crappy 50 to 60Hz conversion. I mean, it's ok...but smooth scrolling gets butchered something fierce.


    I own a boatload of PAL hardware, mostly retro computers like Atari's and Amiga's, and no way do I find it even remotely acceptable to use 50 to 60hz refresh rate conversion.
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    Quote Originally Posted by segasonicfan View Post
    what is the problem exactly? It is a little unclear to me. When you say refresh rate, do you mean flicker or vertical hold issues?
    If using a PAL TV you may have issues with 50/60hz sync signals.

    if using SCART you need to make the PCB Sync into 1vp-p, not 5V TTL coming from JAMMA conn.

    "boosting" the Sync is not usually necessary, it is TTL already (logic high or low). However, JROK sells a great little sync cleaner that fixes issues with messy sync from some PCBs. However, it doesn't sound like thats your problem (MVS has very clean sync).

    if you *must* amplify your sync / adjust it, Extron made a nice sync box you can find on ebay probably.

    -Segasonicfan
    Sorry for the late reply, I've stopped checking that thread after a few days.
    The picture from the MVS was flickering and had some bad sync with the ST-V.
    This was due to a flaw in my first supergun design. I have added potentiometer on the RGB + Sync lines which improved the picture quality tenfold.
    It is confirmed that the pot on the sync line is mostly useless like you mentioned it is TTL.
    I use SCART but I do not understand what you mean by "1vp-p". SCART PIN 8 is connected to +5v from JAMMA connector while I read +12v is more suitable.

    Thanks for the replies!

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    Quote Originally Posted by Yodd View Post
    Well, I don't know the science behind it, but every device I have tried that forced it (GBS boards, XPC-4) or allowed to control it (Framemeister) always resulted in pretty crappy 50 to 60Hz conversion. I mean, it's ok...but smooth scrolling gets butchered something fierce.


    I own a boatload of PAL hardware, mostly retro computers like Atari's and Amiga's, and no way do I find it even remotely acceptable to use 50 to 60hz refresh rate conversion.
    very good to know! thanks for posting this. If micomsoft doesn't handle the conversion well, then definitely nothing else will.

    Sorry for the late reply, I've stopped checking that thread after a few days.
    The picture from the MVS was flickering and had some bad sync with the ST-V.
    This was due to a flaw in my first supergun design. I have added potentiometer on the RGB + Sync lines which improved the picture quality tenfold.
    It is confirmed that the pot on the sync line is mostly useless like you mentioned it is TTL.
    I use SCART but I do not understand what you mean by "1vp-p". SCART PIN 8 is connected to +5v from JAMMA connector while I read +12v is more suitable.

    Thanks for the replies!
    What country are you in? Are you sure your TV supports 60hz Sync? This is what all arcade PCBs use...

    Pin 8 on SCART is a select pin, it is used to detect your input. If you get any image at all it is unlikely this.

    Your other issue is that your Sync is +5v TTL. If you are using SCART, you need to make sure your TV can accept this. many SCART things dont, they pull Sync from composite video. Composite video is around +1V (p-p means "peak to peak" its an AC signal). You need your sync, which is DC, to mimic a composite video signal.

    Viletim taught me about this almost 10 years ago. the thread is still online (cool ) I had the same questions as you did:
    http://nfggames.com/forum2/index.php?topic=2814.0

    You need a voltage divider like he shows. I found that running C Sync through 4k7 x2 resistors with a 1k resistor to ground at the end worked best. This will make a signal your SCART TV is more likely to understand.

    -Segasonicfan

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    Thanks for your reply,
    The TV is 60Hz compatible and takes C sync on PIN 20. The main issue must have came from the RGB lines supplying higher voltage.
    However it was interesting to read about the difference between sync on composite video and composite sync (c sync). I will try out the voltage divider circuit you've proposed and see if there is any improvement.
    Right now the boards I have work well on that TV.
    Thanks for sharing!

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    Jump into the service mode of your Television and see if it has a "free running" sync which can be enabled.

    This will typically give 10+- Hz room of play.

    I don't know what TTL voltage that C-Sync is spit out as. But you'll definitely want to convert that for 75 ohm source terminations.

    If it's around 4.5V logic level, a simple 450ish ohm series resistor on the C-Sync output should do the job. This will form a voltage divider between the 75 ohm termation, dropping it down to around 1000mV or below.
    Last edited by Voultar; 01-08-2017 at 02:01 PM.
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    Thanks for all the insights guys!

    The TV indeed syncs on composite video which I found out by testing a megadrive with both c-sync and composite video. Results were obvious.
    Since then I have tried out the mentioned circuits with no good results.
    1. 75ohm+220uf+0.01uf and pull down potentiometer 2kohm
    2. 75ohm+450ohm....
    Tried several combinations w/o real success. The pot connected to the ground makes it rather useful though.

    Right now I have tapped the composite video directly from the video encoder and it kinda works.
    I guess the LCD TV cannot deliver a better picture in NTSC.

    IMAG0073.jpg

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    Really confused here as to what the problem is, could you describe clearly the issue you are having with a pic or video? that will help to diagnose the issue. I cannot tell much from this pic whats wrong.

    Also, LCDs suck at composite video. especially for neo geo / classic games.

    Quote Originally Posted by Vendest View Post
    Thanks for all the insights guys!

    The TV indeed syncs on composite video which I found out by testing a megadrive with both c-sync and composite video. Results were obvious.
    Since then I have tried out the mentioned circuits with no good results.
    1. 75ohm+220uf+0.01uf and pull down potentiometer 2kohm
    2. 75ohm+450ohm....
    Tried several combinations w/o real success. The pot connected to the ground makes it rather useful though.

    Right now I have tapped the composite video directly from the video encoder and it kinda works.
    I guess the LCD TV cannot deliver a better picture in NTSC.

    IMAG0073.jpg

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    Quote Originally Posted by segasonicfan View Post
    Really confused here as to what the problem is, could you describe clearly the issue you are having with a pic or video? that will help to diagnose the issue. I cannot tell much from this pic whats wrong.

    Also, LCDs suck at composite video. especially for neo geo / classic games.
    Sorry for the late reply.
    Using RGB scart from supergun to LCD.
    A short video is available at the link below.

    https://www.dropbox.com/l/scl/AACucE...GuocVIP7p31P0g

    Thanks for your help!

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    Quote Originally Posted by Vendest View Post
    Sorry for the late reply.
    Using RGB scart from supergun to LCD.
    A short video is available at the link below.

    https://www.dropbox.com/l/scl/AACucE...GuocVIP7p31P0g

    Thanks for your help!
    the video wasnt public so it was kinda hard to download...
    anyway, thats not actually a sync issue. looks like interference or an improper grounding / impedance matching issue.

    your RGB signals are to blame. try a pot to ground (500ohm) and using only one color to the monitor at a time, turn it and see what happens.

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    Thanks!
    Should I do something like this?

    Circuit.PNG

    X1 = 75ohm resistor
    X2 = 0.1uf capacitor
    X3 = 500ohm pot to ground
    Last edited by Vendest; 01-26-2017 at 09:00 AM.

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    @segasonicfan

    I have followed your instruction with a 500ohm pot to ground and tested with one color connected at a time.
    Couldn't really see anything with blue or red only. The noise was there with green and with all of them connected again.

    Now this might sound crazy but the signal gets better or worse depending on the home appliances in use at the same time (microwave, water heater....)
    I have noticed a similar pattern with the original Xbox hooked to the TV with component. Whenever a switch in the house turns on some noise will appear on the screen.

    Overall it is playable since the supergun sync on composite video instead of C sync.
    Thanks for your help!

  19. #19
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    Quote Originally Posted by Vendest View Post


    Now this might sound crazy but the signal gets better or worse depending on the home appliances in use at the same time (microwave, water heater....)
    I have noticed a similar pattern with the original Xbox hooked to the TV with component. Whenever a switch in the house turns on some noise will appear on the screen.
    The power pole outside your house doesn't look like this does it? could be the source of your problems.

    3409369082_4fcfbbbe8b_o.jpg



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