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Re: Altos 5-5AD Restoration

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  • jack99rubin
    Thanks Bill - always helpful to have real world fixit stories. RS232 drivers are always suspect in machines of this vintage since they are easily damaged if
    Message 1 of 2 , Feb 4, 2008
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      Thanks Bill - always helpful to have "real world" fixit stories.
      RS232 drivers are always suspect in machines of this vintage since
      they are easily damaged if terminals/modems etc. are dis/mis-
      connected carelessly.

      They are also susceptible to electrostatic damage since they are
      exposed to the outside world through serial cabling. One of my early
      tech jobs as a grad student was maintaining a long serial line that
      joined two buildings on campus.

      After every thunderstorm, I could be almost certain that at least one
      of these chips would be "blown" - often completely out of it's
      socket - by induced spikes due to lighting. Terminal and computer
      ends were protected by opto-isolators but the intermediate drivers
      were always at risk. The problem was eventually solved by installing
      fiber, but that was a "real" solution that took a bit more resources
      than just stringing cable along convenient fire escapes.

      Jack

      --- In midatlanticretro@yahoogroups.com, "B. Degnan" <billdeg@...>
      wrote:
      >
      > Altos 5-5AD board repair
      > With tutoring from Bob Grieb, I learned how to better troubleshoot
      the
      > motherboard. I can again see the self test boot screen, referred to
      earlier
      > in this thread.
      >
      > Here is what we did (Bob feel free to add/correct):
      >
      > Through careful observation we determined that something was wrong
      with the
      > communications between the terminal and the RS232 port. With the
      terminal
      > plugged in, powered on the computer appeared to stall early in the
      boot
      > process. With the terminal unplugged the computer appeared to go
      farther
      > (drive would spin, hard drive would light). No characters to the
      display.
      > Hmmm...
      >
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