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Powering a dormant Altair 8800

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  • Todd Mollerup
    About six years ago I purchased an Altair 8800 (223115K). The seller told me it was his father s and he knew nothing about it - but the lights came on in the
    Message 1 of 5 , Jul 24 5:20 PM
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      About six years ago I purchased an Altair 8800 (223115K). The seller
      told me it was his father's and he knew nothing about it - but the
      lights came on in the manner expected when he plugged it in. My
      question to the forum is, what is my risk of plugging this machine
      into a power source? Could I cause serious damage to the system? Am I
      better off never plugging it in until it is inspected by someone who
      knows more about the opperations of this machine?
    • eriksklein
      ... I ... If it was plugged in six years ago it s probably safe to say that plugging it in today won t do any harm. Ideally you d want to bring any old gear
      Message 2 of 5 , Jul 24 5:34 PM
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        --- In altaircomputerclub@yahoogroups.com, "Todd Mollerup"
        <tmollerup@...> wrote:
        >
        > About six years ago I purchased an Altair 8800 (223115K). The seller
        > told me it was his father's and he knew nothing about it - but the
        > lights came on in the manner expected when he plugged it in. My
        > question to the forum is, what is my risk of plugging this machine
        > into a power source? Could I cause serious damage to the system? Am
        I
        > better off never plugging it in until it is inspected by someone who
        > knows more about the opperations of this machine?

        If it was plugged in six years ago it's probably safe to say that
        plugging it in today won't do any harm. Ideally you'd want to bring
        any old gear like this up with a variac, but six years probably didn't
        kill the caps. . .

        Erik Klein
        www.vintage-computer.com
        www.vintage-computer.com/vcforum
        The Vintage Computer Forum
      • Craig Landrum
        ... Todd; Using a variac is sensible, but I d just go for it. I ve bought and restored dozens of these things and you have to power it up in order to know
        Message 3 of 5 , Jul 24 6:04 PM
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          On Tuesday, July 25, 2006 at 8:20 PM, Todd Mollerup sent:

          >About six years ago I purchased an Altair 8800 (223115K). The seller
          >told me it was his father's and he knew nothing about it - but the
          >lights came on in the manner expected when he plugged it in. My
          >question to the forum is, what is my risk of plugging this machine
          >into a power source? Could I cause serious damage to the system? Am I
          >better off never plugging it in until it is inspected by someone who
          >knows more about the opperations of this machine?
          >


          Todd;

          Using a variac is sensible, but I'd just go for it. I've bought
          and restored dozens of these things and you have to power it up
          in order to know what needs to be fixed. On the older Altairs
          portions of the row of electrolytic caps tends to go bad and
          results in either no power or low power. but I've yet to see
          one smoke or anything, although I suppose its possible. The
          first thing I did with my Altair was to replace all of them,
          and I've had no problem with power since then. On the boards,
          I haven't seen any of the disk caps go bad, but have heard of a
          few from others. Any electrolytics on boards can go bad like
          the big power supply caps, and I tend to replace them if there
          are just a few on a board. I've needed to replace a few
          of the 74xxx chips, and that's about it. Its usually possible
          to track down a bad 74xxx chip using scope or logic analyzer
          or one of those old Bob Mullen S-100 extender cards with
          the attached probe that shows whether a line is high, low,
          or pulsing. I've seen a few of Mullen's cards on eBay and
          have one myself. To fixed 74xxx problems, you need the
          schematics and those are available for all Altair boards.

          Before I power up a old computer I try and give it a good
          cleaning - blow out the dust and make sure there are no
          solder blobs that have worked themselves down into the bus
          connectors. I use a circuit cleaner and old toothbrush to
          clean any gunk off my boards and follow that by washing it
          with mild dishwashing detergent and warm water - yes water.
          I then let the board thoroughly dry for a day, clean the
          contacts and plug it back in. Even if you skip the board
          cleaning step (its kind of hard to convince youself that those
          chips are actually sealed, isn't it?), try and clean the contacts.

          On the Altairs, be careful of the front panel - that old
          lettering chips off very easy, so don't use anything harsh
          or abrasive to clean it. I wouldn't remove and clean the front
          panel logic board unless it just doesn't work or you need to
          rewire the front panel-bus wiring (a real fun job by the way).

          My recommendation is just to plug it in. If it doesn't work
          it needed to be fixed anyway :-)

          --
          Craig Landrum
          Chief Technical Officer
          mindwrap, inc.
          Phone: (540) 675-3015 x 229
          Fax: (540) 675-3130
          email: craigl@...
        • Steve
          Electrolytic capacitors can go bad on the shelf, either by drying out and developing lower capacitance, or by developing internal leakage. If the power
          Message 4 of 5 , Jul 24 6:31 PM
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            Electrolytic capacitors can go bad on the shelf, either by "drying
            out" and developing lower capacitance, or by developing internal
            leakage. If the power supply caps go bad, they can cause other power
            supply components to fail, which may then result in damage to the
            logic circuitry. High voltage caps, as are used in old vacuum tube
            radios and TVs, are much more prone to failure than the low voltage
            types used in computer power supplies, so I don't think you risked
            much in that respect. In old radios, leaky power supply caps could
            cause rectifier tubes to fail and expensive power transformers to
            fry. Computer PS circuits are more likely to fail in other cheaper
            ways.

            "Reforming" old electrolytics can sometimes return caps to spec, but
            to do it right involves applying increased voltage, while monitoring
            leakage current, over one or more days. Bring up the voltage over
            just a few minutes won't do any good (but it won't do any harm,
            either).

            What you definitely should have done, however, is remove all of the
            daughter cards before powering up. If there were a problem, at least
            you would have saved those boards. Check the 3 buss voltages before
            replacing the boards. (NEVER install or remove S-100 boards under
            power (see the message archives for more on this subject).

            Steve
            ===================================

            --- In altaircomputerclub@yahoogroups.com, "Todd Mollerup"
            <tmollerup@...> wrote:
            >
            > About six years ago I purchased an Altair 8800 (223115K). The
            seller
            > told me it was his father's and he knew nothing about it - but the
            > lights came on in the manner expected when he plugged it in. My
            > question to the forum is, what is my risk of plugging this machine
            > into a power source? Could I cause serious damage to the system? Am
            I
            > better off never plugging it in until it is inspected by someone
            who
            > knows more about the opperations of this machine?
            >
          • Richard A. Cini
            When I got both the Altair and the IMSAI I have, I inspected and cleaned the inside, getting rid of any dust and checking for loose or shorted connections,
            Message 5 of 5 , Jul 25 5:14 PM
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              When I got both the Altair and the IMSAI I have, I inspected and cleaned the inside, getting rid of any dust and checking for loose or shorted connections, looking for things that looked “wrong”. Then, I powered it up with a variac and a 60-watt bulb in series. The bulb will illuminate in proportion to the load, so as I turn up the variac, I can watch for a short by the bulb brightness.

               

              I made this nifty AC load using a plastic gem box, a ceramic lamp holder and a 3-prong cord set. For most things I use either a 60w or 100w bulb depending on the load.

               

              Anyway, I set the variac at increasing voltages for 5 minutes every 10 volts until I reach full line voltage. Even if the seller tells you he powered it up last week, I like to do this so I can establish a level of comfort with the system. It might be overkill, but I’d rather be safe.

               

              Having said that, I’ve never had a blown cap. You also have to watch for tantalum caps on the cards blowing, too, but even those I’ve never blown.

               

              Rich

               

              Rich Cini

              Collector of classic computers

              Lead engineer, Altair32 Emulator

              Web site: http://highgate.comm.sfu.ca/~rcini/classiccmp/

              Web site: http://www.altair32.com/ 

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