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Thread: A little survey for (IBM) CGA owners

  1. #1

    Default A little survey for (IBM) CGA owners

    It's really just a short question or two, so feel free to skip the ramblings and go directly to "1." below...

    I've been toying with some ideas for squeezing interesting things out of the CGA's composite output. As discussed here, not all IBM CGA cards were created equal: early models generate the composite signal differently from later ones, and the effect can be quite visible. Some known IBM part numbers for the Color Graphics Adapter Card are:

    • "early" type: 1501486 (PCB# 1501453), 1804472
    • "late" type: 1501981 (PCB# 1501982), 1504910 (?- possibly a generic box number, card could be either type)
    • unknown type: 1804456, 1804464, 6278550, 6447058 (source)

    I'd like to find out what's out there in the wild - which type of card is more common. Granted, what you guys own might not be a very large sample size, but it's a start. So...

    1. If you have one or more IBM CGA card(s), can you post the respective part number(s) that appear on the board itself?
      .
    2. Bonus question:
      For "unknown type" part numbers, I put together a small test image that could help determine their type. The only catch is, it must be viewed on a composite monitor or TV. RGB monitors (5153, etc) wouldn't tell us anything useful, since RGB output is visually identical across CGA models.

      The .COM file is attached here. If you do have a composite display hooked up, you should be able to tell if your CGA is an early- or late-type model simply by running the program and looking at the results. Here's the actual output from an early-type card (left) vs. a late one (right):


    If you have access to a CGA board, your participation would be appreciated. Hopefully my little experiments will result in cool stuff for you to look at, so there's that.

    Thanks go to fellow poster Reenigne and his awesome XT Server project for help in testing this!
    Attached Files Attached Files

  2. #2

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    How about 3rd party cards? I have a full length CGA card out of a (long gone) rackmount 8088 I can test. Lets hope the card POSTs in a 486 since I don't have a real XT laying around.

  3. #3

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    Clone cards are a whole other can of worms... wasn't really aiming for that, but if the card has a composite output it could be interesting to test.

    Though I'm not sure how well this would work in a 486 system, unless the card has its own clock crystal. IBM CGA cards don't have one - they depend on the system clock to generate the NTSC frequency (a 14.318 MHz oscillator as in the original PC or XT).

  4. #4

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    I have a Datamedia CGA card with composite output in my XT. But I don't use the composite output -- only the 9 pin CGA connector.
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  5. #5

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    Quote Originally Posted by el_VR View Post
    Clone cards are a whole other can of worms... wasn't really aiming for that, but if the card has a composite output it could be interesting to test.

    Though I'm not sure how well this would work in a 486 system, unless the card has its own clock crystal. IBM CGA cards don't have one - they depend on the system clock to generate the NTSC frequency (a 14.318 MHz oscillator as in the original PC or XT).
    I think the card has its own clock. The last machine I tested it in with the composite output was an ITT XTra running at 8Mhz, seemed to work fine. The 486 is an EISA machine with a 8.33Mhz fixed clock on the ISA side.

  6. #6
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    Default

    Quote Originally Posted by el_VR View Post
    Though I'm not sure how well this would work in a 486 system, unless the card has its own clock crystal. IBM CGA cards don't have one - they depend on the system clock to generate the NTSC frequency (a 14.318 MHz oscillator as in the original PC or XT).
    All ISA-compatible systems should have 14.31818 MHz on OSC signal, so the card will work. But this signal's frequency is not tunable (as it is on IBM PC/XT/AT), which as far as I know can cause problems specifically with the color when using component output.

    BTW, I have a CGA clone with composite output. It is a pretty small card, with much of the logic in an LSI IC, but interestingly enough it has a real MC6845 IC on it. If there is an interest, I can test it with TV. (I don't have a CRT-based TV, only an LCD one, so not sure if this will be a valid test).

  7. #7

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    True; not having an IBM-style 'color adjust' trimmer on the motherboard could mean incorrect or missing color output (though not always).

    Anyway, you are all welcome to test non-IBM boards with the program included above - it would actually be interesting to see how they behave compared to true blue models. But my intention here is more to get a rough idea about the distribution of different IBM CGA models (and hopefully, to find out more about the unknown ones); so what I'm really looking for is IBM part numbers.

  8. #8
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    I have three cards:

    CARD #1

    One with black bracket.
    Component side, middle of card: "1804472" stamped in white.
    Photo [here].

    CARD #2

    In my 5155.
    Component side, bottom-left corner: "FS-1501982" stamped in white.
    Component side, left edge: "1501981A4859266819" stamped in white.
    Component side, left edge: "YB 110 1501982 01" on PCB itself (like a copper trace).

    CARD #3

    Spare. Per item 2 above except that "1501981A?970262708" stamped on left edge.
    Photo [here].

    I have nothing suitable for looking at the composite output of the cards (in colour).

  9. #9

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    @modem7: thank you - appreciated!

    Anyone else with an IBM CGA? all I ask for is the number... if you have a TV/composite display you don't even have to open up your machine - just run the program attached at the top.

  10. #10
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    If I don't have to open up the machine, I can definitely run this for you. I've got a composite display hooked up; do you just want a photo of what it looks like?
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