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Thread: AT Wonder 800 EGA card not working on a particular XT clone

  1. #11
    Join Date
    Jan 2013
    Marietta, GA


    The patterns on the screen suggest to me that data is getting corrupted over the ISA bus. EGA/VGA cards usually use various tricks to speed up data transfer so it stands to reason one might be less compatible than others.

    A few thoughts:

    Although Herc and other VGA cards seem to work on this XT clone, it would be interesting to see if a more rigorous test of some type left running for longer periods of time on these working cards would actually produce any errors or not.

    Trying a different BIOS rom would not hurt, although if this is a hardware issue then it would not make any difference. These ERSO style boards can accept a number of different BIOS roms including genuine IBM XT. There are some additional ROMS here that should work. From my own experience the Phoenix ROMs generally have the best compatiblity.

    Just to rule things out, you might try a different power supply. Marginal power can cause odd intermittent behavior.

  2. #12


    Quote Originally Posted by Xacalite View Post
    ATI EGA Wonder 800+ is identical to some ATI VGA card, only it lacks the 15-pin analog output and RAMDAC, also the BIOSes must be different.
    Anyway, both are based on the same 18800-1 chipset, so it would be interesting to try that ATI VGA card in that XT clone, to see whether the incompatibility affects all 18800-1 cards.

    And heh, such things do happen, see eg. this card - and the ALE problem.
    Failed to work with IBM 5150, 5160, and direct clones, but worked fine with other clones.

    "All PCs are compatible, but some PCs are more compatible than others."
    Yes, don't have another ATI VGA card here to test but will keep it in mind should one arrive.
    For now I'll just leave it at "some PCs are more compatible than others"

    Thanks a lot for the input.

  3. #13


    Quote Originally Posted by Ruud View Post
    What about exchanging the ROMs of those clones? If the first XT now works fine, you just copy that ROM and you have two working XTs.
    You mean swapping the rom chips of the XT itself ? Also thought about that but was not sure if they were that interchangeable ?

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