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Thread: is possible to enable color burst from dos on a cga card ?.

  1. #1
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    Default is possible to enable color burst from dos on a cga card ?.

    Have a 286 clone and installed an original "green pcb" ibm CGA card.
    After one of the tantalum caps exploded, it worked great. Composite games look good correct colors.

    But when the computer powers up the composite output is in luma only no color burst.
    So everything looks b/w until i run a game that enable color burst.

    Some games don't do this and the show up in b/w on composite.

    Theirs any program that can run to enable color burst manually ?, at least to see text mode in color also.

  2. #2
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    Have you tried "mode co80"? That should flip the colorburst on, "mode bw80" turns it off.

    Fair warning, color composite text is neigh unreadable. There's a reason bw80 is a thing.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  3. #3

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    Quote Originally Posted by Eudimorphodon View Post
    Have you tried "mode co80"? That should flip the colorburst on, "mode bw80" turns it off.

    Fair warning, color composite text is neigh unreadable. There's a reason bw80 is a thing.
    In addition, there's also that bug (feature?) in the CGA design, where the double pixel clock rate (in 80-column mode) also halves the duration of the hsync pulse. This makes many displays "miss" the color burst, or receive only a partial one, so even in MODE CO80 you may not see any color. This likely accounts for the OP's issue.
    (Possible "feature" rather than a bug, since 80-column text *is* pretty much unreadable in color.)

    Fortunately the hsync pulse duration is programmable, and can be increased a little bit; that's why we added that calibration screen to 8088 MPH. I've also written a small TSR ("TVCGAFIX") to do this from DOS and make the setting stick through mode changes.

    So @soviet9922, perhaps you should try this out and play with the settings: https://int10h.org/blog/2018/08/tvcg...output-for-tv/.

    For best results:
    1. Run TVCGACAL to find your optimal value for horizontal positioning.
    2. Run "TVCGAFIX #" where "#" is the number determined in step 1.
    3. If color is still missing or just wrong, try running "TV80 P". Or "TV80" (no arguments) to see a list of other commands you could try.
    Last edited by VileR; May 17th, 2020 at 03:57 PM.
    int10h.org :: :: :: blog

  4. #4
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    I wish there was some utility that could fix the incorrect artifact colors I get from my Tandy 1000s, but I gather that's some kind of unfixable-in-any-easy-way phase issue.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  5. #5
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    Thanks for the link, i can say that MODE CO80 don't work but TVCGAFIX works great. It indeed enable the color burst and i get all the glamorous multi color 80 column "white" text i could like .
    Anyway most of the software i tested that don't enable color burst probably reinitialize the display because it look B/W.
    Text programs show up in color and that is amazing !, i like to use a big composite tv to play old games.

  6. #6

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    Nice, glad it helps. Note that you can even use this with booters, although that should rarely be needed (use MAKEBOOT with a blank diskette - it'll boot up and apply the fix, then you can insert any other bootable disk, and it should remain in effect).

    On the other hand the TSR cannot work with any game/program that bypasses the BIOS for initializing video. Not much that can be done there, unless you patch the game/program.

    Quote Originally Posted by Eudimorphodon View Post
    I wish there was some utility that could fix the incorrect artifact colors I get from my Tandy 1000s, but I gather that's some kind of unfixable-in-any-easy-way phase issue.
    Yeah, I suppose the problem was that IBM never documented anything about an 'expected' set of artifact colors, and barely even acknowledged their existence, so most of the clone makers couldn't be bothered to get it right either.
    The Tandy 1000 is more of a PCjr clone anyway, and even the PCjr had 'incorrect' colors over composite (compared to CGA). So if IBM themselves couldn't bother...
    int10h.org :: :: :: blog

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