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Thread: PAL Gamecube c-sync

  1. #21
    gorgyrip - Are you using a Samsung? Surely Samsung can fix this issue with a firmware update if enough people complain.

  2. #22
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    Yes, Samsung 40C8000
    I don't think Samsung cares about it because these days most people use HDMI.

  3. #23
    I opened a ticket with Samsung with before/after pictures and they said it been forwarded on to their engineers to look into it. No harm in opening a ticket? Seems ridiculous that we have to mod all our RGB equipment or use an SLG3000 kit to get around the problem which is inherently a Samsung TV issue.

  4. #24
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    It would be nice if they solve the problem. I'm having another problem with. Old systems (nes, snes, pc engine) have huge problems. For exemple:
    1. The title screen of smb3 is full of horizontal lines.
    2. Pc engine street fighter 2. When Honda moves fast his hands, the character is full of horizontal lines
    And the list continues....

  5. #25
    Just use an LM1881 on composite video line to strip out the CSYNC. http://www.gamesx.com/grafx/lm1881.gif

  6. #26
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    Doesnt work, as already mentioned in this very thread.
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  7. #27
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    When using a LM1881 does anyone actually bother to attenuate the output to TV level? Or impedance match? It seems kind of wrong to blame the TV manufacturer for it not working with a bastardized signal. Either of those could be part of the problem. Failing to attenuate could cause the amplifier to oscillate around noise. You also can't count on a TV to have automatic gain correction on EVERY SINGLE SIGNAL so do it right and send inputs the correct level. Correct termination to reduce reflection and ringing is important to consider even on 15 kHz signals which due to their square wave nature REQUIRE components into several MHz for adequate rise times/NOISE IMMUNITY.

    If you design a circuit correctly around a LM1881 (which honestly doesn't really belong anywhere but a TV input, if that) there won't be ANY difference between a true C-sync and separated C-sync apart from negligible delay which probably corresponds to the video being offset to the right by a couple pixels but shouldn't affect operation in the slightest.
    Last edited by Calpis; 04-16-2012 at 06:48 PM.

  8. #28
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    I was thinking a straight forward SCART in>out device with LM1881, placed after an RGB SCART switch, should let multiple consoles benefit from one. Then again if TVs did their job there'd be no reason for this.

  9. #29
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    Quote Originally Posted by Calpis View Post
    When using a LM1881 does anyone actually bother to attenuate the output to TV level? Or impedance match? It seems kind of wrong to blame the TV manufacturer for it not working with a bastardized signal. Either of those could be part of the problem. Failing to attenuate could cause the amplifier to oscillate around noise. You also can't count on a TV to have automatic gain correction on EVERY SINGLE SIGNAL so do it right and send inputs the correct level. Correct termination to reduce reflection and ringing is important to consider even on 15 kHz signals which due to their square wave nature REQUIRE components into several MHz for adequate rise times/NOISE IMMUNITY.

    If you design a circuit correctly around a LM1881 (which honestly doesn't really belong anywhere but a TV input, if that) there won't be ANY difference between a true C-sync and separated C-sync apart from negligible delay which probably corresponds to the video being offset to the right by a couple pixels but shouldn't affect operation in the slightest.

    TV manufacturer is getting the blame because RGB doesnt work with composite video (which pretty much EVERY scart cable will use for any console) as sync. Is that their fault? Maybe... or maybe its Nintendos. But facts are, all other TV's seem fine.

    Oh and the circuit is in the datasheet.


    This only seems to happen with Nintendo stuff (n64 and apparently gamecube) + Samsung TVs.... I suspect its nothing to do with the output of the LM1881, its the source (Nintendo Console, as others work fine)
    Last edited by Bad_Ad84; 04-17-2012 at 02:55 AM.
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  10. #30
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    OK, so the RGB input doesn't work with composite video, but we aren't talking about a SCART input are we? A broken design of a SCART input would be Samsung's bad, but insisting a VGA input for example should gather sync from the composite video input, or that it should accept composite on the Hsync input is reaching.

    ?? There is no circuit in the '1881 datasheet providing a TV-suitable output. It outputs a logic level signal, that's the whole point of the chip, it's your job to turn it into standard sync level* and impedance match. Also from the internal overview the RC components are not of any use for C-sync separation, they're just to trigger Vsync. With pre-AC coupled video you needn't a single other component to use the chip.

    *VGA inputs use logic level signals, but cannot be expected to separate composite sync, though they sometimes do

    I don't know why it would only happen with Nintendo stuff, well besides Nintendo terminating video in the A/V connector in PAL consoles. I'm willing to bet there is no sync separation at all on whatever input is being used and composite is being taken directly as sync which means it's being open-loop amplified and clipped, then as the level shifts depending on the picture content with low frequency components you get false triggers.

    If it actually were the frame timing it's the older consoles I would expect to have problems since they generally have more deviant (sometimes variable) timing. IIRC N64 uses the same timing as MD, PS, PS2 and GC literally has PERFECT video output as it follows BT.601 as seen in all digital TV and DVD players. Misuse is the best explanation.

  11. #31
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    We are talking about scart input. Using RGB with composite video as sync (which is correct for scart to allow fallback to composite video for scart inputs that lack RGB).

    But ALSO

    Using a LM1881 to take out csync and use that gives the same result - but ONLY with N64 for me (and GC according to this thread, but I have never tested that myself) and a samsung TV (from my experience and the constant issue arising from other people and its always a samsung TV).


    The issue is, you get a cross hatch looking interference over the picture. Swapping to CSYNC from the console (rather than via the LM1881) resolves the issue - which is why the OP is looking for pure CSYNC from the GC.
    Last edited by Bad_Ad84; 04-17-2012 at 04:59 AM.
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  12. #32
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    Can composite video be viewed through the same SCART input?

  13. #33
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    How do you mean exactly? by forcing the TV to use the composite video signal rather than RGB?

    Disconnecting pin 16 should do it... 0v is composite 1-3v is RGB
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  14. #34
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    Yes, has anyone tested it though? Maybe it isn't connected to an ADC, or maybe like most TVs there are 3 ADC that are multiplexed to each input. Without 4 there's no chance of simultaneous RGB and digitally separated composite video so the SCART RGB sync must be an analog amplifier/comparator circuit.

  15. #35
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    Not tried it, can do at some point though.
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  16. #36
    Here you go - PAL Gamecube with RGB lead on a Samsung photos.


    Before: RGB Lead. Checkerboard pattern on screen.



    Remove PIN 16 from the cable to force composite:



    After: RGB Cable but forcing composite signal because PIN 16 is removed:


    You know, at this point I prefer composite to RGB on the gamecube - it's blurry but at least the checkerboard crosshatch problem is gone.



    And just for fun, here is an example of N64:
    Before: Normal RGB cable and RGB modded N64 - crosshatch checkerboard problem


    After: Svideo Y Luma pin from N64 multi out wired to composite video in the scart. Perfect image! (using either Svideo Y Luma or the CSYNC pin from the multiout works)
    Last edited by fathertime; 04-17-2012 at 08:10 AM.

  17. #37
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    I really hate this X pattern. In the case of n64, c-sync didn't worked right for me, but luma as sync it's working great.

  18. #38
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    Is the checkerboard static or does it roll or shimmer like composite video artifacts?

    This thread gets more and more confusing. The first thing that come to mind from those pics is that the N64 and probably the GC have dithering on their DAC. It *really* looks like unfiltered dithering assuming it's static and this would be a Nintendo-only problem.

    Using luma instead of composite video gets rid of the checkerboard on GC as well?

    Do they go in and out over time? If so it could have something to do with the comb filter which should be turned off.

    First, composite and luma should not affect video in RGB mode whatsoever. Second, it's very strange that composite but not luma could causes this because they're almost the same signal in terms of varying amplitude over the course of the line. The added chroma in composite would have to be the culprit. Clearly sync has nothing to do with it which makes even less sense about the LM1881. The LM1881 produces the checkerboard but C-sync from the console does does not?? The LM1881 output is a digital signal, it cannot be used to modulate the RGB inputs apart from electrical noise, but there are no video components for the TV to derive green from (as it can with composite and luma).

    It'd be interesting to get to the bottom of this but things aren't adding up:

    -Dithering can be tested by putting a low value capacitor in parallel with the TV input. If this were the issue, it would stand to reason that the presence of chroma causes the TV to change its filter coefficients. No explanation for the 1881 here since it doesn't have chroma.

    -If the TV really does only have 3 ADC and no analog sync input, it must use composite video in place of green similar to YPbPr, but with a different matrix. This would be plausible if C-sync didn't show video at all. In this case chroma would directly affect the image this way, but the pattern couldn't be static, you'd have much lower green bandwidth and again it doesn't explain the 1881.

  19. #39
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    Quote Originally Posted by Calpis View Post
    The LM1881 produces the checkerboard but C-sync from the console does does not??
    When I modded my N64 (some time ago now) it didnt seem to help. Also mentioned above for cory - pure CSYNC apparently didnt resolve it either - only Luma. (which composite -> lm1881 -> TV should give the same as just csync)

    And again, this seems Samsung specific. I have a Philips downstairs and its fine, as well as a few cheapy small tvs around the house which also all work.

    I will retest lm1881 when I get chance, just so thats not leading fault finding astray
    Last edited by Bad_Ad84; 04-17-2012 at 02:56 PM.
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  20. #40
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    Quote Originally Posted by Calpis View Post
    This thread gets more and more confusing. The first thing that come to mind from those pics is that the N64 and probably the GC have dithering on their DAC. It *really* looks like unfiltered dithering assuming it's static and this would be a Nintendo-only problem.
    Hence why I'm such an advocate in favor of putting GC's digital output to use. For 480p games there would no longer be any DAC, ADC, composite video, or YPbPr involved. Purely digital (YCbCr) all through to the TV.

    I'm not sure how many TVs accept interlaced digital however...
    Last edited by Lum; 04-17-2012 at 04:10 PM.

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