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Re: [midatlanticretro] Acquired a PDP-8/E

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  • Dave McGuire
    ... Yes, I d err on the side of mechanical polishing rather than chemical. That s very old plastic. ... Those are little plastic snap-latches. I don t think
    Message 1 of 91 , May 20, 2013
      On 05/20/2013 12:09 PM, Kyle Owen wrote:
      > Yeah, the Sharpie marks made me sad too. Depending on what the switches are
      > made of, I may can use a light solvent, but I think a slight polishing would
      > actually do a better job.

      Yes, I'd err on the side of mechanical polishing rather than chemical.
      That's very old plastic.

      > Also, the top case doesn't seem to latch on. I see
      > two plastic squares screwed into the top case, but I don't see how they'd
      > match up to anything on the power supply side to latch the case down. Do you
      > have some photos of that side?

      Those are little plastic snap-latches. I don't think I've ever seen an 8/e
      on which they worked right. I'd not worry too much about them.

      > Speaking of switches, the SW handle is completely broken, and 0, 1 and 2 of
      > the address/data switches also are touchy. 0 feels as though it's busted and
      > can be moved horizontally, and makes bad noises when switching up and down.

      Well you can usually get away without SW, but you'll need 0/1/2. Let's try
      to ascertain why they feel funny.

      > Are replacement switches as hard to find as I'd think they'd be? I'd probably
      > need just one yellow and a couple of orange ones, if 0 and 1 are broken. Was
      > the common failure point on these simply the handle itself, or the innards
      > holding it to the machine?

      The switches are fairly standard slide switches. I've never had to replace
      one, but I'd be surprised if that were tough.

      The handles have little pegs that stick out on each side, and they snap
      into little metal brackets that are attached to the individual switches.
      Those little pegs break off.

      > I can probably get a variac and bring it up nice and slow, but I know that it
      > was certainly operational within the last 10 years. It came from Auburn
      > University surplus in the 90s and was previously installed in the
      > microfabrication lab as an embedded computer driving a step and repeat camera.

      Cool! I'm guessing your electrolytic capacitors are probably ok. I'd
      still bring it up disconnected from the backplane first to check the PS
      voltages, though. Let me know if you need the pinouts.

      > I have a photo of the tops of all of the boards in that album, but I can take
      > all the cards out and examine them individually.

      Oh? I didn't see that, sorry...imgur's user interface gives me heartburn.
      I will go back and check it out.

      > Will do! Are the keys all the same, or did each switch have its own matching
      > key?

      They're all the same, labeled "XX2247". I keep on on my go-everywhere
      keyring, for luck. :)

      > This has certainly been a "dream machine" for a long time. The front panels
      > were the best, and finally getting to play with one will be a real treat.
      > Thanks for the tips!

      :-)

      -Dave

      --
      Dave McGuire, AK4HZ
      New Kensington, PA
    • Dave McGuire
      ... OS/8 needs a random-access storage device; paper tape won t do it. Magnetic tape drives are *physically* sequential-access, of course, but the TU56 (for
      Message 91 of 91 , Jun 6, 2013
        On 06/06/2013 12:54 PM, Kyle Owen wrote:
        > That looks like a nice product, but yes, it's certainly expensive. I've got
        > some FPGA background myself, along with several different microcontrollers,
        > so I may see about creating something that will work with my high-speed paper
        > tape interface. That could be considered an OS/8 storage device, yes?

        OS/8 needs a random-access storage device; paper tape won't do it.
        Magnetic tape drives are *physically* sequential-access, of course, but the
        TU56 (for example) is logically a random-access, block-oriented device. (with
        highly variable latency ;))

        > I would
        > have no idea how to go about writing a driver for it yet, but perhaps it'd be
        > in my best interest to start reading up on the commands for the card and then
        > learn more about OS/8. Do you have any suggestions on recommended reading for
        > this?

        If this was a generally-directed question...The book you want for "most
        things OS/8" is the "OS/8 Handbook". It is excellent. Try to find a paper
        copy if you can, but it's available in PDF on bitsavers:

        http://bitsavers.trailing-edge.com/pdf/dec/pdp8/os8/OS8_Handbook_Apr1974.pdf

        -Dave

        --
        Dave McGuire, AK4HZ
        New Kensington, PA
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