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Thread: Boards from a 3270 PC

  1. #1

    Default Boards from a 3270 PC

    I have the boards from an IBM 3270 PC (type 5271). The mainboard has a lot of bodge wires. Reading the Byte review, it's hinted that the mainboard may not be completely standard.

    https://archive.org/stream/byte-maga.../n237/mode/2up

    Are all these bodge wires standard? Is it a standard 5160 mainboard?

    I got these boards, when I bought the PC chassis from a scrap dealer many years ago (early 90s). I just bought the chassis and PSU - and the boards came along... Back then I had no idea what all the strange boards were. I just removed them, and have had them since

    3270-8.jpg

    3270-9.jpg

  2. #2
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    I am not surprised it has "bodge wires" as it was pretty much thrown together and had the odd operating system that can run DOS programs alongside the 3270 emulation program, and its likely that mods were needed to get this to work. It was only ever available as a custom unit. You could not order the bits to convert an ordinary PC to a PC3270. In fact you will also find such fixes on many IBM cards.
    Dave
    G4UGM

    Looking for Analog Computers, Drum Plotters, and Graphics Terminals

  3. #3

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    Is the operating system special? I thought is was just standard DOS, with a 3270 TSR. That's the way 5250 terminal software works (for S/36, AS/400 etc). I've worked with those a lot, but never 3270 stuff until it was just software and TCP/IP

    I'm not sure I ever tested the motherboard. I guess I should do that... I remember testing the video card, and getting no output. But I probably didn't have the keyboard card installed, so the video card had no BIOS. I also don't know what monitor is correct for this card. I probably had an EGA monitor back then.

    Should I replace the 15 orange firecrackers before powering up the board?

  4. #4

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    Here are the "special" cards from the system. The video card is three boards sandwiched together. The centre board can be used on it's own, and the other two add graphics support and custom character set support (if my research is correct).

    The small board converts the keyboard from AT to XT protocol, adds timing circuits and the BIOS for the video card.

    The single full-length board is the "host connect" board.

    3270-1.jpg

    3270-2.jpg

    3270-3.jpg

    3270-5.jpg

    3270-6.jpg

    3270-7.jpg

    There must have been a floppy controller as well. But perhaps I used that elsewhere sometime during the last 25+ years

  5. #5
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    It would be nice if you could dump the BIOS if you have a way to do that

  6. #6
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    also, I've been working on putting one together and have everything now except the main board if you don't have a need for it

  7. #7

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    Quote Originally Posted by Al Kossow View Post
    It would be nice if you could dump the BIOS if you have a way to do that
    There are three of them

    The two chips on the mainboard are a TMM23256P, which has the standard 27C256 pinout, and a MK37050-4, which has the 27C64 pinout. So my EPROM programmer should be able to read those.

    The BIOS chip on the keyboard card is a ceramic package EPROM, but I can only read the date code and "JAPAN" without removing the label...

  8. #8

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    Quote Originally Posted by Al Kossow View Post
    also, I've been working on putting one together and have everything now except the main board if you don't have a need for it
    I don't need a "special" XT mainboard, if it actually is special. Perhaps the BIOS contents can reveal something...

  9. #9
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    Quote Originally Posted by mcs_5 View Post
    Is the operating system special? I thought is was just standard DOS, with a 3270 TSR. That's the way 5250 terminal software works (for S/36, AS/400 etc). I've worked with those a lot, but never 3270 stuff until it was just software and TCP/IP

    I'm not sure I ever tested the motherboard. I guess I should do that... I remember testing the video card, and getting no output. But I probably didn't have the keyboard card installed, so the video card had no BIOS. I also don't know what monitor is correct for this card. I probably had an EGA monitor back then.

    Should I replace the 15 orange firecrackers before powering up the board?
    The software is what differentiates the 3270PC from a PC with a 3270 card. Its really a sort of multitasking hypervisor. More details here:-

    https://en.wikipedia.org/wiki/IBM_3270_PC

    if you have a graphics display it ma be you have a 3270PC/G which used a different base unit.....
    Dave
    G4UGM

    Looking for Analog Computers, Drum Plotters, and Graphics Terminals

  10. #10
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    there are details here
    https://www.seasip.info/VintagePC/5271.html

    John must have dumped the firmware at some point, considering all of the details on how it works

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