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Thread: K4 keyboard keyswitch question

  1. #1
    Join Date
    Feb 2015
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    Default K4 keyboard keyswitch question

    Refurbishing a Kaypro 4 from the '80s, I recently went through the keyboard. (The machine won't start so I hadn't tested the board beforehand.)

    When I removed the keycaps, which were grubby, I could see that the housing was full of dust and there was evidence of a cola spill. I took it apart as far as I could, cleaned surfaces without immersing anything (except the keycaps) and put it back together. I then tested the keyboard with a K II running Perfect Writer [insert pejorative comment here.]

    A total of seven or eight keys were dead, some on the numeric keypad and some in the middle of the alpha characters. I assume this is due to a liquid spill.

    While I was cleaning I wanted to see what was under the "stems" but as they resisted removal, and not knowing any better, I relented. It looks to me as though the mechanism is different from the K II board, which has foam pads above a capacitive trace. It looks like the bottom half of each switch is soldered to the backplane and the upper half ("stem") snaps in and is held by plastic tabs.

    So my question is this: Can I pry out the upper parts by compressing the tabs and lifting out the stems, or is there another technique, or are they not made to be taken apart?

    Thanks for your replies.

    -CH-

  2. #2
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    With the K4/83 now booting I was able to test the keyboard against its "proper" machine. I observed the same dead keys (Y,H,L,DEL on the left and 2,3,5,7 and 9 on the right keypad) as when tested with a K II. I disassembled the keyboard once again.

    The board has a small SMK insignia among the traces and I found some reference materials on line: [https://deskthority.net/wiki/SMK_J-M0404_series] which leads me to believe these are J-M0404 series switches. I couldn't find any direct replacements as NOS but I will be experimenting with substitutions.

    After finding a picture of the disassembled switch [https://deskthority.net/wiki/File:SM...assembled.jpg] I was hopeful that I could clean the switch in-situ. However, after desoldering the dead switches I think these are not made to be disassembled, which is unfortunate.

    Edit, 2:30 PM EDT: I was mistaken; the switches can be taken apart, cleaned, reassembled and restored to operating condition. You will have to desolder them from the circuit board and pry them out of the carrier plate first because the tabs that hold top to bottom pry outwards and the plate restricts access.


    Pictures of the dirty 3/4 dozen below. Also confirmed cola spill as root cause of failure.

    -CH-

    KSW.jpg
    Last edited by clh333; April 16th, 2018 at 10:35 AM. Reason: correction

  3. #3
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    Most handset cords use 28 AWG conductors or smaller. But if you're willing to crimp up your own, the sky's the limit--just buy the proper cable in bulk and get out your telephone connector crimper.

    https://www.philatron.com/coil-cable/coiled-cords.php

  4. #4

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    Quote Originally Posted by Chuck(G) View Post
    Most handset cords use 28 AWG conductors or smaller. But if you're willing to crimp up your own, the sky's the limit--just buy the proper cable in bulk and get out your telephone connector crimper.

    https://www.philatron.com/coil-cable/coiled-cords.php
    Shouldn't this go in his other thread which is about the keyboard cable?
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  5. #5
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    Quote Originally Posted by Stone View Post
    Shouldn't this go in his other thread which is about the keyboard cable?
    "PoTAYto, poTAHto; I need all the help I can get.

    Thanks, Chuck.

    -CH-

  6. #6
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    De-soldered, removed, disassembled, cleaned, reassembled, tested, remounted and re-soldered all nine keys. Reassembled keyboard and tested on the K4 successfully, Q.E.D. It was something of a pain but at least there is no foam to deteriorate on this version of the board as is the case with the K II Keytronic capacitive switches.

    -CH-

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