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Thread: IBM/C128 CGA conversation, capture, and VGA display success stories

  1. #1
    Join Date
    Aug 2006
    Chicagoland, Illinois, USA
    Blog Entries

    Default IBM/C128 CGA conversation, capture, and VGA display success stories

    (This is an oft-repeated topic, so I felt there should be a dedicated thread for it.)
    Every so often, people see the cheap "CGA2VGA" or "CGA2RGB" arcade adapters on ebay and wonder aloud if that is a good solution for replacing their aging or broken IBM CGA or Commodore 128 monitor. Unfortunately, those adapters either don't work, or produce subpar results (only half the colors displayed, colors transposed, or both). Proper handling of digital TTL CGA requires three things:

    1. TTL RGB to analog RGB conversion
    2. Proper handling of the intensity ("I") pin so that all 16 RGB colors are output
    3. Handling of the color "yellow" so that it is displayed as "dark brown" (which matches what CGA monitors do internally)

    While there are rumors of commercial products from the late 1980s and early 1990s that can perform these conversions (Extron produced some, but I have not yet tested the units in my possession), most success stories are from homebrew adapters. These adapters massage CGA TTL into analog RGB, then another device either converts the resulting analog RGB to VGA (where a cheap "CGA2VGA" device IS used) or performs capture directly with a capture card that can deal with 15.7KHz horizontal frequencies. Here are a few success stories that I've seen:

    Here are other solutions that should work but thus far have been unverified by me:

    • Another Richard Goedeken's design board, this time revised by John Carlsen: (I have this in my possession but have not yet verified its functionality)

    Please feel free to add to this thread with additional success (or failure!) stories.
    Offering a bounty for:
    - A working Sanyo MBC-775 or Logabax 1600
    - Music Construction Set, IBM Music Feature edition (has red sticker on front stating IBM Music Feature)

  2. #2


    I've got one of these:

    That works with the GBS-8220 to convert to great. I have not carefully studied to confirm how the yellow/dark brown coloring displays. Only thing missing is a nice case to hold it all...need to do something with mine rather than having the boards laying around.

    I seem to recall reading that the board you reference is basically the same thing as what ajacocks put together in the link above. Maybe a slight tweaking, and also SMD rather than thru-hole.

    Prior to that, I actually contacted the folks at Gonbes who confirmed, as we know, that TTL CGA would not work direct into the GBS-8220. However, they did tell me that the GBS-8219 would do the job. Unfortunately, it does not handle the intensity pin...and it is quite expensive.



  3. #3


    I use an original NEC MultiSync which connects to CGA, EGA and VGA cards directly, works perfectly and alleviates the need for three monitors.

    I've got one left in storage.
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

  4. #4
    Join Date
    Dec 2014
    The Netherlands


    I have something of a question:
    These CGA TTL-to-RGB circuits would also work on low-res EGA. But have you ever seen any that would also support the extra EGA colours for high-res?
    I would think that it would not be too difficult to add EGA support to such a circuit, for the people who designed them. But perhaps they never thought of that, because they concentrated only on CGA and/or C128.

  5. #5


    That C128 adaptor looks very neat. I put together a simple resistor ladder circuit to do the same thing here:
    No brown fix though.

    Also, an Extron 202xi (not rxi) will do this, they are available cheaply on eBay.
    A scandoubler like the GBS units is still required. I was never 100% happy with these though, and ended up buying a CGA monitor eventually.
    For Euro people a Philips CM8833 or similar makes an excellent CGA monitor, I prefer mine over my IBM 5153.

  6. #6
    Join Date
    Dec 2012
    Russia, Moscow

  7. #7


    I was thinking... could this conversion be done with a small FPGA like this?

  8. #8


    CGA has more colors than 16 shades of grey???
    (From a HP 100LX user)

    Well i have been tempted to get one of these 20 dollar china converters, but if you have an ebay one where they show the input sockets you already know these ain't gonna work.

    These 150 Dollar china converter thingies work though. Well more like "150 to 200 Dollar"... Prices vary on these, but i have seen them as low as 150 bucks (If that really counts as "low").

    And then there is this one guy who sells modern TFTs (Well modern as in "the year 2003 just called and wants its TFT displays back") converted to CGA. I'd be interested in that since it also features lovely jumpers to go to mindblowing green or B&W MONOCHROME...

    HELL YEAH MONOCHROME (Note: This sentence meant to be typed in all caps and bold...Oh yeah here we are again...)

    I'd be tempted to get one just to see the internals. Well but shipping to Japan or Germany (where i usually hang out) might be even more expensive...

    I'd be interested in feedback for these Richard boards and other homemade stuff. Not so really interested in C-128 as I always used mine on a TV Set (Works fine. At least for the German C-128D...I swear!), but for CGA these converters would be great.

  9. #9


    There's also the Miracle LT15A-TTL, a 15" LCD monitor which claims to do MDA, CGA, and EGA:

  10. #10


    Quote Originally Posted by vwestlife View Post
    There's also the Miracle LT15A-TTL, a 15" LCD monitor which claims to do MDA, CGA, and EGA:
    I have one of those, works great. Pricey but has them for $275. Also takes up way less desk space and I don't have to worry about an antique monitor dying.


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