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Thread: Osborne I - no disk drive response

  1. #41

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    Gentlemen - could someone comment on why I see *no* matrix (cross hatches) at all in those two exposed areas of my keyboard? But the cross hatches are clearly visible on the one from the Desktopia site?

    Before I proceed with the slitting, poking, and membrane separation ... I need to be sure a "membrane matrix" is what I've actually got. I'm afraid I don't follow Dave's suggestion about squeezing the 5 key area; do you mean pressing down on it? What would I be squeezing? I'm really surprised I see no cross hatching at all.

    Thanks.
    Tom M.

  2. #42
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    2,313

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    They *must* be there, otherwise the keyboard won't work! I think you just can't see them because of the deterioration that has occurred...

    Read up on how the keyboard works at https://en.m.wikipedia.org/wiki/Keyboard_technology. You have a full-travel membrane keyboard. Basically, you have two plastic layers (top and bottom) printed with the matrix pads (the 'bread' of the sandwich) separated by a 'spacer' that has holes where the key intersections are (the sandwich filling). When you press a key, you are forcing the top contact through the hole in the spacer to make contact with the bottom contact.

    Yes, squeeze = press.

    What I think has happened is the silver has deteriorated (causing the black/blue colour) and somehow (chemical growth maybe) caused a bridge through the air gap spacer between the two conductive pads of the switch.

    Hope this makes sense now?

    Dave

  3. #43

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    OK - certainly makes sense now. I've been mystified by mine not showing evidence of a matrix - just a discolored grey/blue "sheen" in that area instead.

    If this deterioration has spread, as it appears it has, I think this would indeed be reason for replacement of the keyboard. It is unfortunate that there is so little (none?) information on refurbishing that membrane, altho' as you say, it was never meant to last this long. Like my 1953 MG!

    MG apples Ercoupe.jpg

  4. #44
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    2,313

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    Nice car!

    Rather bizarrely at Church this morning on our PC used for visuals guess what, the right cursor key stopped working! This is the most important key we have as it is used for moving the 'slides' on... Fortunately, we had an old keyboard that we could replace it by. Tested the 'duff' keyboard on another PC - yep, the right cursor key is as dead as a dodo. Replacement now ordered !

    Even modern PCs (with a membrane keyboard I would guess) fail!

    The reality with a membrane keyboard is that it is not designed for repair. Like modern electronic assemblies (microwaves, fire and burglar alarms etc.) if they fail, you replace the bit that has failed, or replace the entire unit. It is not like a keyboard with a separate switch for each key that can be replaced providing you can get the individual key switch units themselves.

    Why go for a membrane keyboard in the first place? It is probably a cheaper sub-assembly than a key switch variant I suspect.

    Yes, you now have a problem of sourcing a replacement. But, you will find that a replacement may also be well into its life expectancy...

    Welcome to the hobby of keeping vintage computers going... It is like vintage cars, you have to spend money on them to keep them running.

    Dave

  5. #45

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    Nice car indeed! Single owner from new in 1953 until I bought it two years ago. All original: paint, leather upholstery, canvas weather gear, brightwork, engine, even original tools and repair kit, etc. A true time capsule.

    I can't help but make the comparison: my O1 works perfectly, boots, processes, drives, CRT, etc. But without the keyboard, it's just a lump.

    My MG works perfectly: Starts on first crank with full choke, settles to an 800 rpm idle, pulls right out in first gear, accelerates through the gears to 80, then safely brakes to a halt. But if the ignition coil were to fail, it's just a lump. Fortunately, it uses a standard 12 volt coil, which are readily available!

    Onward through the fog!
    Tom M.
    (PS - good luck with the Brexit situation. Sounds like a real quagmire.)

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