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Thread: Got IBM 5251 display terminal

  1. #1
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    Default Got IBM 5251 display terminal

    Hi guys, got a IBM 5251 display terminal from a friend.
    not my picture is this model:




    The terminal have seen better days the keyboard cable is cut, but i have bot ends of it.
    The keyboard is dirty but seems fine.

    The computer have some corrosion in the metal inside and is so dirty that have to wash it inside using a hose before getting it inside home.

    Therese something interesting that can be do using this terminal ?, because been token ring so no way to connect it to a modern system.

    Also where i can get a service manual and/or schematics for this ?.

  2. #2
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    It certainly isn't token ring! couldn't find a service manual, but a guide is here:-

    http://xahlee.info/kbd/i4/ibm_5250_m...1980_996c4.pdf

    maintenance manuals are here:

    http://www.bitsavers.org/pdf/ibm/525x/

    probably of interest to the owner of a mid range box such as s36/s38/as400 which used these screens...
    Dave
    G4UGM

    Looking for Analog Computers, Drum Plotters, and Graphics Terminals

  3. #3
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    It is purely a terminal for Twinax based machines and is not itself a computer.
    = Excellent space heater

  4. #4
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    Ok finish cleaning it up, and now things look much better


  5. #5
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    Tested it and in place of blowing up and melting down like i imagined
    Worked at least it powers up, the fan start the cathode in the picture tube glows.

    But no response from the digital part of the monitor, testing at the psu looking in the service manual i can see that all the DC voltages are ok they are variable but as specified on the documents

    Don't care much about that but what i found interesting is that the monitor part is separated from the rest of the unit the monitor runs at 120 volts and have it own power supply.

    Also in the service manual i can see that the motherboard send (video horizontal and vertical sync) to the monitor.
    The monitor board seems a very simple design not sure the horiz and vert frequency is not mentioned on the service manual.

    Thinking about hooking a CGA video card output to it to see if that works and if its 15 khz horizontal suppose is the most estandard don't think that this use MDA frequency for the display but i can test that.

    What is not normal at least for me from the monitor is that the cathode glow in the tube but i don't see any bright from the anode you now if you have a unplug from the computer and powered crt theres always a faint glow, not sure is this can be a fault but if the cathode is on i should have something as image on the tube i suppose ?.

    Some info from the service manual


    not 100% how to interpret this pinout numbers.



    Last edited by soviet9922; January 10th, 2018 at 05:59 PM.

  6. #6
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    No console lights? Check your switches. Again, there is very little smarts in the terminal as you might of noticed so you will not get some sort of fancy greeting screen when you turn it on (refer to this: https://www.youtube.com/watch?v=3eE35DOcCAA ). They rely heavily on a Terminal Controller that sits between the stations and the computer.

    A word of caution. The keyboards from these terminals are HIGHLY sought after by the window lickers at Deskthority, Geekhack and some of the Reddit subforums. Something about keyboard mechs in recent years has become some sort of a social status. These people and their ideas do not mix well with us VC folk for reasons. Ignore them.
    = Excellent space heater

  7. #7
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    Just got a single led half on and nothing else from the digital side of this.
    When searching for information about the terminal ended up seeing a bunch of videos of people using this keyboards seem to be the best keyboard ever or something like this ?.
    Also found that they sell an adapter from it to usb and must say i found this interesting it can be an use for the keyboard in case the terminal ends up non servisable.
    If i can recover the display and using the adapter i can install a small board using linux and hercules emulator to give some main frame feeling ?.

  8. #8
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    Normally I'm against restuffing terminals like that, however no offense you are far enough off the path I don't think it would be feasable for you to find it another home, or a machine to run it on unless by chance you come across something like an IBM 5364 or another similar system that's nice and small for a midrange that will support Twinax terminals. I don't think it would be too hard to restuff a machine into that.
    = Excellent space heater

  9. #9
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    I'm located in Uruguay, i don't know anyone here that is in vintage computer even less that have an old ibm twinaxial mainframe.
    So i have to do like always all stuff by myself, try to salvage the most possible and get a good use out of it on my backyard.
    Using the original display could be much cooler than just gutting everything and stuffing a new crt inside it :P

  10. #10
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    You can convert this thing (for effect) to be either a CGA (monochrome) or MDA driven adapter. All the signals you need are on the edge connector of the video board.

    Back in the day, I did this with a bunch of Fujitsu terminals of the same sort (twinax fed). They worked fine as monochrome displays.

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