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    Repairing (some) cheap keyboards.

    Sorry I don't have any pictures, I did these repairs at work and didn't have a camera. No capacitors involved!

    Most inexpensive keyboards today use an internal construction like the one shown in the first picture here:

    http://en.wikipedia.org/wiki/Keyboard_technology

    The 3rd layer down is the internal wiring from the keys to the logic board. The logic board is often (but not always) located in the upper right corner of the keyboard, above the keypad. (Generally where the numeric lock, caps lock, and other LEDs are seen.)

    We had a batch of Keytronic KT800USBBUS-C keyboards, which were failing one by one, in every case losing the space bar and certain other keys. So I opened one up to see what was going on. It turned out that the connection from the internal wiring layer to the logic board consisted of two sets of exposed contacts on plastic (mylar?) sheets. These were held together solely by the pressure of a foam rubber "spring", which pushed on one side on the back of the case, then on the internal wiring layer, the extension from the logic board, and finally the front side of the case. After seeing this, I found that all of these keyboards would work correctly if one pressed down on the top of the keyboard above this connection.

    The first attempt at a fix was to cut a thin piece of cardboard (the backing from a yellow lined paper pad) and fasten it to the back of the keyboard above the spring. This was done by roliing up some scotch tape into tubes, sticky side out, and taping the cardboard in place. This repair worked for a while (months) but eventually failed.

    What else to try? Well, there were hollow cylindrical standoffs coming up from the front of the keyboard on both sides of the spring. These appeared to be screw mounts, but were unused. It looked like some earlier incarnation of the design had used a physical clamp over the spring. This had been eliminated, leaving the two closest screws to the clamp a couple of inches away in either direction. Over time the case plastic would loosen up, the spring wouldn't have enough oomph to keep the connectors together, and some keys would stop working. Of course, it worked long enough to test good at the factory, and in most instances, long enough to outlast the warranty.

    To repair this problem on a test keyboard two screws were scavenged from another failed keyboard. A lot of careful measurements were made on the positions of the two unused posts with respect to the used screw posts, and then this was mapped onto the back of the case, in this case using the corresponding screw holes, to determine where the two new holes were to be drilled. Then the new holes were drilled (with a drill press for the first one, later I just used a hand drill). Reassembled the keyboard, screwed in the two borrowed screws, and voila, the keyboard worked again.

    A small cardboard template was made from the first repaired keyboard. It indicated the new screw hole positions with respect to other features in the molding. For the subsequent keyboards the keyboard was disassembled, the template used with a center punch to mark the two new holes, the holes drilled, the cardboard spacer added (probably not necessary with the clamps, but it does up the spring pressure slightly), and the keyboard reassembled with screws in the two new holes. In every instance this let the keyboards function again.

    The extra screws were 4-24 pan head hi-lo screws from McMaster-Carr

    http://www.mcmaster.com/#97975a110

    These were very similar to the other screws in the keyboard, except with a different finish and driver (Philips instead of T8 Torx). I only needed 18 of them (2 * 8 keyboards plus 2 missing screws) but the smallest number that could be ordered was 100. So I'm set to repair a large number of crappy keyboards should they ever come my way.

    The materials cost was about $10 for the screws, which was a lot less than 8 new keyboards would have run. I think this fix should last a reasonably long time because the front and back parts of the case are now firmly held together right at the edges of the rubber spring. Most likely several years from now the rubber in the spring will get old and not push hard enough, but I will cross that bridge when I come to it.

    #2
    Re: Repairing (some) cheap keyboards.

    Very interesting repair. Most poeple wouldn't even think about fixing a keyboard - out with the old, in with the new.

    I've had only 1 keyboard give me a little bit of problems - it was an old Logitech Delux 104 (don't remember exact model). After many years of service, some of it's keys wouldn't work that well.
    Turns out there was just a bit of crud under some of the rubber domes. I just cleaned them, and all was well again.
    Actually, it was a lot more work that, though. This being an old keyboard, it had separate rubber domes for each key rather than one big rubber sheet with domes. Also, this keyboard doesn't use contact grid sheets separated by an insulating sheet but rather the rubber domes have graphite contacts in them and they pressed directly onto a single contact grid sheet. Because of that, I had to clean every single rubber dome for every single key separately. Took me about half hour for that.
    Of course I figured if I'm going that far, I might also wash the plastics - and I did. I gave the top part with the keys a good scrubbing with a water, detergent, and a toothbrush.
    It came out spotless and even smelled like new .

    Needless to say, this is still my favorite keyboard.

    Comment


      #3
      Re: Repairing (some) cheap keyboards.

      Originally posted by momaka View Post
      Of course I figured if I'm going that far, I might also wash the plastics - and I did. I gave the top part with the keys a good scrubbing with a water, detergent, and a toothbrush.
      It came out spotless and even smelled like new .
      I like to clean keyboards with 409. Windex will work in a pinch, but it takes much longer to get the keyboard clean. The 409 removes accumulated skin oil/dirt without scrubbing.

      For the quality keyboards, where the keys can be removed, pop them all off, put them in a plastic lidded storage container a little bigger than all the keys, fill it about 1/3 of the way up with 409, and soak for 10 minutes or so, shaking gently once and a while. Decant the 409 and put in water, rinsing a couple of times this way until the 409 smell is gone. Finish up with distilled water (if your water is as hard as ours is, otherwise there will be water spots.) Lay the keys out on some type of low lint towel to dry.

      With the keys off one can clean the top of the keyboard carefully with a 409 dampened paper towel. If there are lots of little nooks and crannies it is best to take the keyboard apart and wash it in the sink.

      When everything is completely dry, reassemble, and it looks like a new keyboard. The only downside is that as keyboards age the plastic can become fragile, so that keys which are supposed to snap off may break instead.

      Also, for a quick "clean", just turn the keyboard over and shake it gently. Tapping the back once and a while. All sorts of little bits of crud get down between the keys and can be released this way. Think of it as keyboard dandruff ;-). I have over the years repaired a few keyboards where keys had stopped working because they had this crud jammed into the switch mechanism - repairs in those cases just meant carefully cleaning out the crud.

      Comment


        #4
        Re: Repairing (some) cheap keyboards.

        Originally posted by mathog View Post
        I like to clean keyboards with 409. Windex will work in a pinch, but it takes much longer to get the keyboard clean. The 409 removes accumulated skin oil/dirt without scrubbing.
        I don't mind the scrubbing that much. It's only to get some of the dirt loose and get soap/detergent everywhere. After that, I give it a strong blast with hose, which is what removes most of the crud and whatnot.

        Originally posted by mathog View Post
        For the quality keyboards, where the keys can be removed, pop them all off, put them in a plastic lidded storage container a little bigger than all the keys, fill it about 1/3 of the way up with 409, and soak for 10 minutes or so, shaking gently once and a while. Decant the 409 and put in water, rinsing a couple of times this way until the 409 smell is gone. Finish up with distilled water (if your water is as hard as ours is, otherwise there will be water spots.) Lay the keys out on some type of low lint towel to dry.
        Wow, distilled water? That takes keyboard cleaning to a whole new level .

        Originally posted by mathog View Post
        Also, for a quick "clean", just turn the keyboard over and shake it gently. Tapping the back once and a while. All sorts of little bits of crud get down between the keys and can be released this way. Think of it as keyboard dandruff ;-).
        Lol
        I used to do that before, but it doesn't get everything out. And yes, I did share and tap the keyboard - actually it was more of a pounding that tapping, but anyways (my Logitech has a metal backplate, so not much of a problem for it).

        Originally posted by mathog View Post
        I have over the years repaired a few keyboards where keys had stopped working because they had this crud jammed into the switch mechanism - repairs in those cases just meant carefully cleaning out the crud.
        Yes, that's what was happening with my Logitech and why the keys didn't work.
        Back when I was in high school, I used to eat every once in a while in front of the computer and that's where part of the crud came from. Nowadays, I don't. Moreover, I wash my hands too before and after I use the computer. It really does help keep things much cleaner.
        Last edited by momaka; 07-26-2011, 10:23 PM.

        Comment


          #5
          Re: Repairing (some) cheap keyboards.

          Interesting.

          Somewhat unrelated but I know that the IBM M2 keyboard often had issues due to poor capacitors. They're actually supposedly really nice clicky keyboards so worth a repair.
          http://geekhack.org/showwiki.php?title=Island:5065

          Comment


            #6
            Re: Repairing (some) cheap keyboards.

            I tried to repair my keyboard after the spacebar broke. It could only be pressed in the center or on the right side. On this keyboard, there was a metal bar under the key that slid into two clips. One of the two clips had broken, so I glued it back on and reinforced the other. A few days ago, the spacebar broke again. Both clips had broken off this time, so it could only be pressed in the exact center. I was able to fix it again, but I might need a new keyboard soon.

            Comment


              #7
              Re: Repairing (some) cheap keyboards.

              Originally posted by lti View Post
              On this keyboard, there was a metal bar under the key that slid into two clips. it could only be pressed in the exact center.
              Typical keyboard problem.
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                #8
                Re: Repairing (some) cheap keyboards.

                The metal thing is the stabilizer and it basically allows for you to hit longer keys off center with ease.

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                  #9
                  Re: Repairing (some) cheap keyboards.

                  When gluing that plastic (with solvent, like MEK, lacquer thinner, or the brush-on stuff sold by hobby shops, not super glue), it can take 48-72 hours for the joint to develop full strength, as I learned when I tried to fix a plastic tailgate latch, several times in a row.

                  Comment


                    #10
                    Re: Repairing (some) cheap keyboards.

                    I like to clean keyboards with 409. Windex will work in a pinch, but it takes much longer to get the keyboard clean. The 409 removes accumulated skin oil/dirt without scrubbing.

                    For the quality keyboards, where the keys can be removed, pop them all off, put them in a plastic lidded storage container a little bigger than all the keys, fill it about 1/3 of the way up with 409, and soak for 10 minutes or so, shaking gently once and a while. Decant the 409 and put in water, rinsing a couple of times this way until the 409 smell is gone. Finish up with distilled water (if your water is as hard as ours is, otherwise there will be water spots.) Lay the keys out on some type of low lint towel to dry.

                    I just open the keyboard up, put the electronics and the film stuff inside away then go to the bathroom with the keyboard.

                    Take out the shower nozzle, turn on warm water, put my finger to partially cover the water output, therefore making a high pressure stream of water.

                    Excellent and simple way to clean the gunk from below the buttons - as I direct the high pressure stream on the buttons they basically lift up by themselves and the bad things go away in the drain.

                    After this, just some dish washing liquid dissolved in plain water works great, leave it in a bucket or something for 5-10 minutes, then wash again with plain cold water and dry it up. If I'm in a hurry, pull out the hairdryer, set it on lowest heat and dry out everything.

                    Comment


                      #11
                      Re: Repairing (some) cheap keyboards.

                      Originally posted by mathog View Post
                      These were held together solely by the pressure of a foam rubber "spring", which pushed on one side on the back of the case, then on the internal wiring layer, the extension from the logic board, and finally the front side of the case. After seeing this, I found that all of these keyboards would work correctly if one pressed down on the top of the keyboard above this connection.
                      A year later and two of the repaired keyboards have failed again, in exactly the same way. Since the screws are all still tight the only remaining variable is the spring pressure exerted by the neoprene like rubber, which apparently degrades over time. On opening the keyboard the rubber only partially rebounded, whereas a year ago they opened up much more, which tells us that these rubber "springs" are a really poor design - unless the goal is to sell more keyboards. I could not find any similar rubber at work to replace these "springs" so patched it temporarily with another thin piece of cardboard (from the back of a steno-pad), this time between the rubber and the circuit. Even with the degraded spring that was still enough force to keep the circuits in contact.

                      As an aside, a similar rubber "spring" in the latch of a sort of scanner at work used to fail regularly too - and the replacement part from the equipment manufacturer was ridiculously expensive. A couple of years ago I got sick of that and put in a small wide metal spring from the local hardware store, held in place by its own force and a bit of tape. That has held up much longer than any of the official parts did, and it cost 1/40th as much.

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                        #12
                        Re: Repairing (some) cheap keyboards.

                        Not a bad idea. some gaming keyboards may be worth it to repair because of the new price. Then again it has been awhile since I bought one so the prices may have come down.

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                          #13
                          Re: Repairing (some) cheap keyboards.

                          I'm beginning to think a better approach would be to drill two holes through both the plastic sheet and the little circuit board, then put a bit of metal as a bridge between the holes, and bolt it in place. Kind of like the way a capo is used on guitar strings. This would eliminate the need for the not very effective spring. Spacing is pretty tight though - there may not be enough space for the holes and little bolts and bridge.

                          Comment


                            #14
                            Re: Repairing (some) cheap keyboards.

                            Originally posted by mathog View Post
                            I'm beginning to think a better approach would be to drill two holes through both the plastic sheet and the little circuit board, then put a bit of metal as a bridge between the holes, and bolt it in place. Kind of like the way a capo is used on guitar strings. This would eliminate the need for the not very effective spring. Spacing is pretty tight though - there may not be enough space for the holes and little bolts and bridge.
                            Question/suggestion...
                            Why not try to solder wires from the sheet to the circuit board? Or are there too many contacts? Or too small, perhaps?

                            Seems to me like you're doing a lot of work to get these keyboards working again. If I were you, I'd just get a bunch of surplus old Keyboards from pawn shops and the like and just clean them a bit. The older they are, the longer they will last .

                            I got several keyboards from work last winter. One of them is one of those beige Dell QuietKey (or is it LoudKey, IDK ) keyboards (model RT7D5JTW).
                            After washing it, I think this is my second most favorite keyboard after my old Logitech Y-SA2 Deluxe 104 keyboard.

                            I also got 2 slightly newer black Dell Keyboards (model RT7D20). Those are fairly nice too, but after washing, the long keys such as the Space bar and Shift become hard to press if you press them along the edges. Apparently, the lubricant they use on the mechanism of the keys gets dissolved by laundry detergent. The beige Dell QuietKey didn't have that problem because it uses a slightly more robust mechanism that doesn't need lubrication to work. In fact, the mechanism it uses is excellent - there's barely any side-play on the keys.

                            Comment


                              #15
                              Re: Repairing (some) cheap keyboards.

                              Originally posted by momaka View Post
                              Question/suggestion...
                              Why not try to solder wires from the sheet to the circuit board? Or are there too many contacts? Or too small, perhaps?
                              The conducting material on the mylar sheet isn't shiny and is probably either some funky alloy or a conducting organic compound. In any case, it is not a simple copper, aluminum, or tin conductor. Even if solder would bind to the conductor (which is I think unlikely) the mylar under it would have melted at least 100C below the melting point of the solder.

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