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Re: [midatlanticretro] Re: So... Who's coming this weekend? And what should I bring?

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  • Mr Ian Primus
    ... I ve already done a fair bit of troubleshooting. The only thing I lack is card extenders. I ve got the schematics and the microcode listings printed out,
    Message 1 of 15 , Jun 29, 2012
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      --- On Fri, 6/29/12, s100doctor <hjohnson@...> wrote:

      > You will need an oscilloscope, docs for BOTH boards with
      > schematics, a hex extender. A book of TTL logic data would
      > help (I will bring that for my use.) And (excuse me) some
      > clue about using these. But I don't think a public email
      > discussion, is a very good place to discuss how to repair a
      > control board or to describe whatever difficulties you
      > yourself may have in its repair. Certainly not in 24 hours.

      I've already done a fair bit of troubleshooting. The only thing I lack is card extenders. I've got the schematics and the microcode listings printed out, and I did spend a fair bit of time checking the TTL associated with the nonworking function (deposit[1]). I do not fully understand the microcoded portion of the logic, although I have verified the bits I do understand. Another set of (experienced) eyes would also definitely be beneficial here.

      Lacking card extenders, I've had to extend the individual signals from specific chips to probe them. This gets tedious and is difficult. I'm pretty sure I can find the fault, given full access to the board while it's installed in the computer.

      > Someone will have to commit to bring extender cards.

      One person has already mentioned that they'll bring some extenders.

      > You will apparently have an opportunity to compare your
      > NONworking 11/05, to a WORKING 11/05, side by side. Take
      > advantage of that as best you can, down to the chip and
      > logic level.

      That was how I was able to quickly and easily verify that my fault lies on the Control board. I've got a friend that has a working machine. We've compared some things between the machines, and done some swapping and testing, but again, lack of card extenders makes individual logic checks tedious and difficult. I DO know that my computer works properly when a functional Control board is installed. And that the symptoms move to a working computer when my faulty Control board is installed.

      But yes, having card extenders, and a working control board borrowed from one of MARCH's machines would greatly help to clarify what is supposed to be happening on the board when the deposit switch is pressed.

      -Ian


      [1] For those of you playing along at home, the fault is that when the deposit switch is pressed, the address increments but nothing is written to memory. Examine works. The CPU can write to memory itself - if you write a program that will alter memory when run, toggle it in with a good Control board, then swap in the faulty Control board, and run the program, it WILL write to memory. The only fault is that the deposit switch itself does not write to memory. I've tested the flip flops and gates connected directly to the deposit switch, and everything appears to function correctly. *Part* of the problem is that I don't fully understand exactly how the microcoded portion of the logic is supposed to work, however. Another difficulty is that the available schematics are of very poor quality and are difficult to read in places. Either they're bad scans, or just good scans of bad photocopies. Either way, they do add an extra level of frustration to an already
      difficult process.
    • Dave McGuire
      ... 11/05 CPU cards don t. Precisely three have hit eBay in the past 4-5 years. The 11/05 is one of the earliest PDP-11s, from 1972. Not many of these
      Message 2 of 15 , Jun 29, 2012
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        On 06/29/2012 11:06 AM, s100doctor wrote:
        > http://bitsavers.org/pdf/dec/pdp11/1105/
        >
        > may have sufficient hardware docs, otherwise look around if you don't have them already. "bring" them on a laptop.
        >
        > These old cards go by on eBay but there's none there today.

        11/05 CPU cards don't. Precisely three have hit eBay in the past 4-5
        years. The 11/05 is one of the earliest PDP-11s, from 1972. Not many
        of these systems were made (comparatively speaking), and they dried up
        many years ago.

        Other Unibus cards, appropriate for use in that system, aren't tough
        to find. The two CPU boards, though, really need to be repaired because
        finding replacements is nearly impossible now.

        -Dave

        --
        Dave McGuire, AK4HZ
        New Kensington, PA
      • s100doctor
        Glad Ian has done a fair amount of testing and diagnosis down to the chips. But...it s too much work to diagnose chips by email. (shrug) so I respect his
        Message 3 of 15 , Jun 30, 2012
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          Glad Ian has done a fair amount of testing and diagnosis down to the chips. But...it's too much work to diagnose chips by email. (shrug) so I respect his analysis but won't reply to it.

          Reading between the lines, Ian needs a set of bus extenders to expedite his work, and maybe better schematics. Someone with 11/05 prints or photocopies of them would expedite his work.

          I misplaced my DEC bus extenders, I actually looked for them. But Gesswein will bring his.

          Herb
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