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Model 4 membrane keyboard - anyone know how to fix it ?

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    Model 4 membrane keyboard - anyone know how to fix it ?

    I have a membrane keyboard on a model 4 and to be honest they are a bit rubbish but I hate to throw out a whole keyboard because one or 2 key switches are non-responsive...

    Has anyone had any luck fixing one of these types of keyboard and if so how is it done?

    Cheers,

    Ian.
    *There is never a charge for Tech Support even if you don't purchase from me - We are Enthusiasts Helping Other Enthusiast and that is just the way it is

    #2
    This is a disassembled keyswitch from my Model 4:



    That particular switch had four solder points on it, so it took a little care to remove it.

    If the rubber dome is intact then the problem is probably the little black disc on the underside of it. The black disk loses whatever magical properties are that make the circuit complete. Usually if you just press harder it works, but at normal typing pressures it is not enough. There are kits out there for restoring remote controls that consist of a chemical that you apply to the black disc to restore its conductive properties - find one that works, and then tell me. ; - 0

    I have to do almost my entire keyboard .. that project has been on the shelf a long time because of the effort require to remove all of the key switches.

    Comment


      #3
      If those black disks are the same as the ones in the similar mechanism contained inside a Commodore PET keyboard what worked really well for me was swabbing the metal contacts clean with alcohol, dabbing the rubber disk clean with water, and finally before putting it back together *very* gently stroking the side of a sharpened pencil lead across the disk. Two keyboards that were essentially completely unresponsive after a "normal" cleaning were good as new after that.
      My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

      Comment


        #4
        That's the older style keyboard. Tandy released a newer version with the Gate Array and 4D if I remember correctly. Mine has the same as TRS-Ian does. And it a totally different beast. And I am not sure how to clean the contacts in them TRS-Ian. Good luck
        *FrankG*

        Comment


          #5
          Thanks Frank.

          For people's reference, here is the keyboard chronology:

          1983: Maxi-switch keyboard (see mbbrutman, above) with separate bezel for the first few thousand NGA M4s
          1983-4: ALPS keyboard with separate bezel for all the rest of the NGA M4s
          1984-5: membrane keyboard (so shitty the manufacturer didn't even put their name on it) with integrated bezel for all GA M4s
          1985-6: membrane keyboard (ditto) with extra backspace key and integrated bezel for the first batch of M4Ds
          1986- : back to ALPS keyboard with separate bezel for the rest of the M4Ds.

          Here's someones video explaining how membrane keyboards work: http://www.youtube.com/watch?v=34IFo90MuoA

          Looks like I'm just going to have to take one apart and see what I find...

          Ian.
          *There is never a charge for Tech Support even if you don't purchase from me - We are Enthusiasts Helping Other Enthusiast and that is just the way it is

          Comment


            #6
            The black dot in the green plunger has no magnetic properties. It is conductive rubber.

            If you get some Rubber Renue (used for resurfacing belts and rollers in VCR and audio equipment), dab a little on the "dot" with one end of a q-tip and wipe it off with the other, it will work fine. You might want to clean up those two contacts on the base with a soft pencil eraser.
            Legacy Computers and Parts

            Sales of, parts for, and repairs to, Vintage and Legacy computers.

            Comment


              #7
              Originally posted by Druid6900 View Post
              The black dot in the green plunger has no magnetic properties. It is conductive rubber.
              I don't think anybody said anything about magnetic properties. The phrase used was "conductive properties."

              An application of a chemical designed to restore the conductive properties will work well. I have a container of "Keypad fix" which contains carbon and a binder in liquid form; apply it and leave it for 24 hours to dry. It's similar to the pencil lead approach above, except that the carbon won't be loose and floating around.

              Is Rubber Renue conductive, or does it just make the rubber more pliable?

              Comment


                #8
                For the older style keyboard where a few keys don't want to respond try this. Take the plunger if it's still in good shape (In Mikes picture the Green part) and super glue some copper tape to the piece of carbon/conductive rubber. The glue seems to like the carbon/conductive rubber and adheres very well. Have used couple of years now this way in my older MIV and Works every time! But then I have said this before!
                Attached Files
                Last edited by Chromedome45; June 14, 2012, 04:02 AM.
                *FrankG*

                Comment


                  #9
                  Originally posted by Chromedome45 View Post
                  For the older style keyboard where a few keys don't want to respond try this. Take the plunger if it's still in good shape (In Mikes picture the Green part) and super glue some copper tape to the piece of carbon/conductive rubber. The glue seems to like the carbon/conductive rubber and adheres very well. Have used couple of years now this way in my older MIV and Works every time! But then I have said this before!
                  I have done this mod with aluminium foil and super glue in calculators but I hadn't very lasting results.Maybe with copper works better..

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                    #10
                    2 Years on and still working! I think copper is a much better condictor. Plus my copper tape is about 2 times thicker than Aluminum foil.
                    *FrankG*

                    Comment


                      #11
                      Originally posted by mbbrutman View Post
                      It's similar to the pencil lead approach above, except that the carbon won't be loose and floating around
                      Yeah, in the case of the PET I decided I didn't care too much if the pencil lead eventually got loose because the design of the PET keyboard makes it really easy to get in there and clean/renew it. (Removing the PCB exposes all the plunger tips at once.) If you have to desolder the keyswitches and pry them all apart separately I'd recommend something more "professional".
                      My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                      Comment


                        #12
                        Try looking at;

                        Caig Laboratories Part #: K-CK44-G

                        It works on remote controls and other
                        rubber type switches.

                        Comment


                          #13
                          Originally posted by mbbrutman View Post
                          I don't think anybody said anything about magnetic properties. The phrase used was "conductive properties."

                          An application of a chemical designed to restore the conductive properties will work well. I have a container of "Keypad fix" which contains carbon and a binder in liquid form; apply it and leave it for 24 hours to dry. It's similar to the pencil lead approach above, except that the carbon won't be loose and floating around.

                          Is Rubber Renue conductive, or does it just make the rubber more pliable?
                          Sorry, I thought I saw magnetic in there somewhere.

                          Actually, rubber renue is a resurfacer. It takes off a thin layer of oxidized rubber and presents a new conductive surface since the rubber is conductive all the way through.
                          Legacy Computers and Parts

                          Sales of, parts for, and repairs to, Vintage and Legacy computers.

                          Comment


                            #14
                            Here is a picture of the Model 4D membrane keyboard, from the top it looks like any other Model 4 keyboard:

                            membrane1.JPG

                            and here is what it looks like underneath:

                            membrane2.JPG

                            Ian.
                            *There is never a charge for Tech Support even if you don't purchase from me - We are Enthusiasts Helping Other Enthusiast and that is just the way it is

                            Comment


                              #15
                              Yep same one as I have in my MIV GA!
                              *FrankG*

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