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Re: Repair of MARCH Commodore PET 2001 chiclet keyboard

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  • crock_aka_rob
    ... That was me providing many of the responses on that thread but unfortunately the title is misleading as there isn t much of the content focused on the
    Message 1 of 32 , Nov 30, 2012
      --- In midatlanticretro@yahoogroups.com, B Degnan <billdeg@...> wrote:
      >
      > We have more than one chicklet keyboard at MARCH? There have been a few threads and documents on the web, cctalk and vintage-computer.com in particular, that detail how to restore a chicklet keyboard. I personally have not done this work before but maybe I have something in my stuff about it.
      > Bill
      > --
      > Sent from my PDP 8/e.
      >

      That was me providing many of the responses on that thread but unfortunately the title is misleading as there isn't much of the content focused on the keyboard. However, it did make me think to ask Jeff whether there is a pattern to the non-working keys? Are you sure the problem is in the keyboard matrix itself and have you ruled out the PIA chip (6520 Peripheral Interface Adapter?)

      I have restored several of them, and unless there's multiple designs, they pretty straightforward. Responding to Jeff's mail the plunger is basically rubberised carbon. I don't know exactly what polymer is used but neither is it important. As linked to, there is plenty of kits for repairing such keypads but personally I've never had to resort to coating the plunger with anything on a PET keyboard. As long as it bridges the gap with something less than a few hundred ohm's resistance, it'll be enough to pull the input line of the PIA low and for the key-press to register. For me, it's been enough to be *very* diligent in the cleaning. As a rule, I dismantle the keyboard, thoroughly clean the PCB with ISO-propyl alcohol and, if necessary, something very mildly abrasive if there's visible corrosion, but that's never been a problem for me on 2001 keyboards. If there is, try a pencil eraser. Wipe off the PCB with a lint free cloth because even dust on the pads can make a difference.

      Then there's the problem of the plungers. Now someone has been sticking foil on them, it may be impossible to now clean them up again. As the rubber plunger deforms when the key is pressed, I can't see this being a good long-term solution unless the foil is really wafer thin and flexible. I can see it coming away from the plunger and causing more problems than it solves. I individually clean the plungers with a pad of lint free cloth. You can use cotton buds (I think you guys call them q-tips or something) but again, you need to ensure you don't leave lint behind.

      Finally, the PCB needs to be carefully but firmly screwed in place. If the board is riding high because of debris trapped between it and the keyboard frame, you will get poor contacts. All the screws also need to be present and evenly tightened for the same reason.

      In all, they're actually pretty good quality even if not fun to type on, the construction having been lifted from Commodore's desktop calculators of the time. If you really have no joy, I will swap it for a working one of mine.

      Rob
    • joshbensadon
      ... Oh well :( It was fun throwing ideas out there just the same. ... Rare or not, it definitely looks much cooler! ... I was hoping to see Bryan on the
      Message 32 of 32 , Dec 3, 2012
        --- In midatlanticretro@yahoogroups.com, "Jeffrey Brace" <ark72axow@...> wrote:

        > > Was my other advice helpful?
        >
        > Not really. I just used ordinary household aluminum.

        Oh well :( It was fun throwing ideas out there just the same.

        > I don't know the reason why there is a blue label. I just know that it is
        > more rare than the black one.

        Rare or not, it definitely looks much cooler!


        > You can ask Bryan Pope, he knows a lot more
        > about the PETs than I do.

        I was hoping to see Bryan on the weekend at World of Commodore, but I missed him.

        Cheers,
        Josh
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