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Re: [midatlanticretro] Re: Tech weekend -- everyone's projects ...

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  • Mr Ian Primus
    ... Chances are, it s the notorious little RFI filter capacitor in the power supply. These fail with frightening regularity - the particular ones used in these
    Message 1 of 15 , Jul 3, 2012
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      --- On Tue, 7/3/12, David <davesica@...> wrote:

      > I may also be in the running for a "last to smoke" prize. As
      > I was demonstrating the newly-revived Osborne back at home
      > to my daughters, fieldingĀ  questions like "So which
      > version of Photoshop does it run? 1.0? Heh, heh, heh!" and
      > "Where's the mouse?" daughter #1 suddenly yelled out "Dad,
      > it's on Fire!" and with a fresh appreciation of how portable
      > this computer is NOT, I hustled it out the back door. Oh
      > well, it continued to run right up until I pulled the plug
      > so hopefully a few caps will be the limit of the damage.

      Chances are, it's the notorious little RFI filter capacitor in the power supply. These fail with frightening regularity - the particular ones used in these old computers break down with age and fail with a plume of smoke. They don't cause damage to other components when they go, and the computer will actually function without it.

      Basically, the capacitor goes across the AC line at the input of the power supply, and suppresses the switching noise from the supply, reducing the amount of RFI the computer generates. They're "line rated" capacitors, designed not to fail in a mode that causes them to make the chassis hot, or create another unsafe situation. You should only replace them with components of the same or greater safety rating (X2 rating is current and common).

      If you open the computer and carefully inspect the power supply, you should find it easily, it will be a square yellow clearish plastic block, with a crack in it and burnt stuff coming out. It's usually a .1uf 250V X rated RIFA brand capacitor.

      You should really replace the part, but simply desoldering or clipping it out will suffice. It's not critical for the operation of the computer - it's simply there to reduce the noise on the power line, to help prevent the computer from screwing with television reception and stuff like that.

      -Ian
    • s100doctor
      ... http://www.retrotechnology.com/restore/marchfixit5_12.html A work in progress, it s my description of the event and the work I was immediately involved in,
      Message 2 of 15 , Jul 4, 2012
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        --- In midatlanticretro@yahoogroups.com, "Evan Koblentz" <evan@...> wrote:
        >
        > Could everyone who attended send a list message about their projects from this weekend?

        http://www.retrotechnology.com/restore/marchfixit5_12.html

        A work in progress, it's my description of the event and the work I was immediately involved in, or witnessed. I was simply too busy to follow everyone's work. It was, after all, a work session.

        Many of the photo links are "broken" - I need to process down the photos to manageable size. I run a 20th century Web site, not a modern one. It's my particular interest, to "report" on the event.

        I'll do what I can to add briefs on other people's work, Web links. I'm taking the liberty of quoting some of the self-descriptions in this thread. Those who attended, contact me privately to correct my errors and omissions (a contact email is at the bottom of my Web page.)

        What did I do? I worked closely with Bill Degnan on both of our Proc Tech SOL computers. Mine came up! After decades! Bill's did not, his 8080 processor (with or without in-circuit emulator) can't seem to read or write to memory or ROM. But I did not have time to complete my repairs of the keyboard, to replace all the capacitive foam/Mylar pads. It was usable anyway, "naked".

        I was prepared to add a working Northstar floppy controller but did not have a double-sided drive (or time) to try out Bill Sudbrink's SOL/N* disks - thanks for a copy of those.

        PT co-designer Lee Felsenstein looked over our shoulder to verify the operation of the divide-by-seven circuit that feeds the 8080 with a 2MHz clock from a 14MHz crystal. He read the schematic and worked it out in front of me & Bill. He's "still running on all cylinders" as we old-guys say. He had something to say about making more engineers, later in the afternoon.

        I also cleaned up my PDP-8/F, which was not nearly as "dusty" as the MARCH PDP-8. David inspected my system and commented. BTW, his work on debugging the MARCH 8's serial port was simply amazing field service. It was fun to watch him clean the club's 8.

        Oh - when the A/C timed out, I reset the controls, and figured out that no one had opened all the A/C vents in the room. Brilliant. I, and many others, noted the lack of grounded outlets in the room - namely, ONE, plus one in an adjacent room. *Evan, take note.*

        Otherwise, I took photos and ate pizza, and asked hard questions. I'm pleased with how it went.

        Herb Johnson
      • s100doctor
        ... A mistake many people make, and made during the event, was to run the Osborne without opening the vent. It will cook itself. Open the vent. Otherwise,
        Message 3 of 15 , Jul 4, 2012
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          --- In midatlanticretro@yahoogroups.com, "David" <davesica@...> wrote:
          > Ian Primus made my day by providing a fresh boot disk for my Osborne 1, which to my great delight woke right up and ran after napping for perhaps the past 20 years.

          > I may also be in the running for a "last to smoke" prize. As I was demonstrating the newly-revived Osborne back at home to my daughters, daughter #1 suddenly yelled out "Dad, it's on Fire!"

          A mistake many people make, and made during the event, was to run the Osborne without opening the vent. It will cook itself. Open the vent.

          Otherwise, various caps will short and smoke. Find them as soon as possible after ignition. Then tag 'em so you can repair them later. Wait a day, a week, and you will lose the smell of it, it will stink up the rest of the machine.

          Herb
        • Evan Koblentz
          ... Lesson learned! Will keep the vent open on the museum display unit. Thanks for showing me that -- I didn t know there was a vent. I thought that was some
          Message 4 of 15 , Jul 4, 2012
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            >> A mistake many people make, and made during the event, was to run the Osborne without opening the vent. It will cook itself. Open the vent. Otherwise, various caps will short and smoke.

            Lesson learned! Will keep the vent open on the museum display unit. Thanks for showing me that -- I didn't know there was a vent. I thought that was some kind of service panel.
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