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IBM 5155 Keyboard Problem

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    IBM 5155 Keyboard Problem

    I get an IBM 5155 for 250$ wich is a great price, i think.
    Everything is ok, but the Keyboard isnt. If I hit keys, sometimes
    there appears letters on the screen wich arent they, what i've hit.
    So if i press E, there appears EX, and with O, there appears OU.
    What can I do there? (I havent testet it with the CP/M OS, so just with the ROM BASIC because of floppy problems on other computer)

    #2
    Originally posted by Manello View Post
    What can I do there?
    It sounds like a faulty keyboard, but I guess that the problem cause could be the keyboard circuitry on the motherboard. It would be good to quickly prove which of the two is the cause.

    If you look inside the 5155, you will see a black cable that runs from the front-panel keyboard connector, along the right side, to the motherboard. You can see the black cable in the photo that is [here]. If you have an XT-class keyboard (an AT-class one will not work), then you could unplug the black cable from the keyboard socket on the motherboard, plug your XT-class keyboard into the socket (when the the 5155 is powered off), and see if that changes the symptom.

    Comment


      #3
      I will try that over the weekend

      Comment


        #4
        That's a cool looking machine there Manello. Very tight and tidy.

        Here's another photo showing the connector at the back: http://oldcomputers.net/pics/5155cards.jpg

        I too have a faulty keyboard on my portable 8088 clone (Eagle PC "Spirit"). Fortunately it has an outside DIN connector for an external keyboard, which works fine, but PC/XT compatible keyboards are becoming hard to come by.

        I have heard somewhere, (can someone more knowledgeable than I confirm?), that keyboards have their own ROM which can occasionally develop Alzheimer's. For example, I once had a notebook that forgot how to type a "c". It was NOT a physical switch problem, because shift-c produced a "C" just fine. I couldn't figure it out, and the computer was not worth saving so I stripped it of RAM and its dinky hard drive and threw it away. But I would like to repair the Eagle if at all possible.

        If the ROM thing is true, it would be the second reason popping up today to urge me to buy an EPROM programmer of some sort.

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          #5
          Keyboard hasnt got his own ROM. If you press a Button, The Keyboard sends a package of Data in bits to the computer. Only keaboards with "extra programmable keys" habe got theyre own rom.
          (The Package of Bits is determinatet of an Matrix in youre keyboard, and it is generatet physical when pressing buttons)

          Comment


            #6
            First rule out the cord being the cause of the problem.
            @ BillDeg:
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              #7
              Mine does this kind of thing. Leave it running for ten minutes or so, then give the keyboard and bit of a bash on the bench (not to destruction!), restart and mostly it will work OK until next time you turn it on

              I thought I read somewhere that they have a foam in them that disintegrates and goes dusty, but someone else on there posted that there is no such foam.

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                #8
                Originally posted by pearce_jj View Post
                Mine does this kind of thing. Leave it running for ten minutes or so, then give the keyboard and bit of a bash on the bench (not to destruction!), restart and mostly it will work OK until next time you turn it on

                I thought I read somewhere that they have a foam in them that disintegrates and goes dusty, but someone else on there posted that there is no such foam.
                All model F buckling spring keyboards have foam padding *inside* the spring assembly.
                Here's a photo of the foam.

                I would wager the problem has to do with the ancient electrolytic capacitors on the controller board. Those should be replaced. They'll probably be axial.

                Comment


                  #9
                  At post #5, the OP indicated that he was going to do a simple test to prove that it was indeed the keyboard at fault.
                  In my opinion, I don't think it is worth adding posts to this thread until the result comes in.

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