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Re: [midatlanticretro] Crow Bar circuits

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  • Systems Glitch
    ... Not with an assembled computer, but I ve had a bench power supply fry a whole board of TTL and a really nice LED display. There was an intermittent ground
    Message 1 of 10 , Sep 7, 2012
      > Has anyone ever had damage done to their computer due to a voltage spike from a failed power supply? I keep thinking, it might not take much to have a regulator or output transistor short and deliver the full unregulated voltage to a computer. Or if there's a variable resistor for voltage adjustmen, that could go open?

      Not with an assembled computer, but I've had a bench power supply fry a whole board of TTL and a really nice LED display. There was an intermittent ground connection to the ground supply of a 3-terminal 5 Volt regulator. When it momentarily went open or Hi-Z, output voltage would jump to something above 10 Volts on the +5 rail. It was intermittent, so that supply took out a few things before I realized it was something with the supply. A crowbar circuit would have prevented that.

      On the other hand, I've got a 5 Volt modular supply that smoked a power resistor because the crowbar circuit falsely triggered. Most of them are composed of a trigger circuit and SCR, so the crowbar stays on until power is completely removed.

      Thanks,
      Jonathan
    • Bill Sudbrink
      ... Are we talking vintage or modern? If modern, yes. I had an Antec 450 watt supply fail and take the entire computer... motherboard, memory, CPU, video
      Message 2 of 10 , Sep 7, 2012
        Joshbensadon wrote:
        > Has anyone ever had damage done to their computer due to a voltage
        > spike from a failed power supply?

        Are we talking vintage or modern? If modern, yes. I had an Antec
        450 watt supply fail and take the entire computer... motherboard,
        memory, CPU, video card, hard disk and DVD player with it. After
        the "event" the supply was completely dead and made a delightful
        stink. I didn't have time or inclination to do a "post mortem" so
        I have no real idea of the details of the failure but the only usable
        electronics left were the case LEDs and the case fans.

        Bill S.
      • joshbensadon
        ... Ouch, I guess that power supply said If I m going down, I m taking everyone with me! . I m talking about a Mark-8 computer. It has a linear power supply
        Message 3 of 10 , Sep 7, 2012
          --- In midatlanticretro@yahoogroups.com, "Bill Sudbrink" <wh.sudbrink@...> wrote:
          >
          > Joshbensadon wrote:
          > > Has anyone ever had damage done to their computer due to a voltage
          > > spike from a failed power supply?
          >
          > Are we talking vintage or modern? If modern, yes. I had an Antec
          > 450 watt supply fail and take the entire computer... motherboard,
          > memory, CPU, video card, hard disk and DVD player with it. After
          > the "event" the supply was completely dead and made a delightful
          > stink. I didn't have time or inclination to do a "post mortem" so
          > I have no real idea of the details of the failure but the only usable
          > electronics left were the case LEDs and the case fans.

          Ouch, I guess that power supply said "If I'm going down, I'm taking everyone with me!".

          I'm talking about a Mark-8 computer. It has a linear power supply from Condor with the typical 723 regulator and what I thought was a 2N3055 but after removing the cover I found they are SDM4004 which look like darlington (hFE=1000) equivlents of the 3055.
          I haven't finished building the computer yet and was deciding if it's worth my while to install Crowbars on the 5V and -9V supply. Which after reading your story it's a definite yes.

          Jonathon and David talked about the Crowbar frying the power supply, but a proper Crowbar circuit should include a fuse right before the SCR.

          PS. I'm also helping a friend with an Analog Computer and I think it should have crowbar circuits installed too. There are no chips in it, only transistors, but I imagine these are all fragile transistors.
        • Bill Sudbrink
          ... On reflection, I should revise that a little. The keyboard, mouse and LCD display also survived. The repair ended up taking almost an entire
          Message 4 of 10 , Sep 7, 2012
            Joshbensadon wrote:
            > --- In midatlanticretro@yahoogroups.com, "Bill Sudbrink"
            > <wh.sudbrink@...> wrote:
            > >
            > > Joshbensadon wrote:
            > > > Has anyone ever had damage done to their computer due to a voltage
            > > > spike from a failed power supply?
            > >
            > > Are we talking vintage or modern? If modern, yes. I had an Antec
            > > 450 watt supply fail and take the entire computer... motherboard,
            > > memory, CPU, video card, hard disk and DVD player with it. After
            > > the "event" the supply was completely dead and made a delightful
            > > stink. I didn't have time or inclination to do a "post mortem" so
            > > I have no real idea of the details of the failure but the only usable
            > > electronics left were the case LEDs and the case fans.
            >
            > Ouch, I guess that power supply said "If I'm going down, I'm taking
            > everyone with me!".

            On reflection, I should revise that a little. The keyboard, mouse and
            LCD display also survived. The "repair" ended up taking almost an entire
            frustrating weekend. It was my wife's computer. Initial evaluation:
            "Oh, the PS died. I'll just pop out to MicroCenter and get a new one.
            You'll be back up and running in an hour." One new PS later (tested
            independently) and the machine still dead: "Well damn. The PS took the
            motherboard with it. It's going to take a little longer than I thought."
            I went ahead and bought a new motherboard, CPU and memory. Later I
            confirmed that the old memory and CPU were also dead. I put everything
            back together and got "beep codes" (Oh, I guess the speaker survived too)
            for no video adapter. I should have checked the hard disk and DVD drive
            right then but didn't. Back to MC for a new video card. Installed it
            and promptly got "No boot device". The HD wasn't spinning. Checked the
            DVD drive and found it dead as well. It should have occurred to me to at
            this point to be surprised that the keyboard, mouse and display were
            still working but I was so angry that I just stomped back to MC for a new
            HD and DVD. Then spent the rest of the weekend reinstalling the OS and
            all of my wife's applications.

            Bill S.
          • David Gesswein
            ... That was the purpose of my comment to make sure you thought about proper design of it. Commercial designs didn t always get it right. The current/energy
            Message 5 of 10 , Sep 7, 2012
              On Fri, Sep 07, 2012 at 02:26:22PM -0000, joshbensadon wrote:
              > Jonathon and David talked about the Crowbar frying the power supply, but
              > a proper Crowbar circuit should include a fuse right before the SCR.
              >
              That was the purpose of my comment to make sure you thought about proper
              design of it. Commercial designs didn't always get it right. The
              current/energy the fuse can deliver before it blows is also an issue
              on picking the SCR.

              > PS. I'm also helping a friend with an Analog Computer and I think it
              > should have crowbar circuits installed too. There are no chips in it,
              > only transistors, but I imagine these are all fragile transistors.
              >
              You can look up a couple of the part #'s to see the breakdown voltage.
              Since the analog computers weren't normally trying to use the fastest
              transistors they may have a good margin on breakdown voltage.
            • joshbensadon
              ... Ouch, that must have been very frustrating! The guys down at the store must be thinking You again? . Well, this would be one of those things in 20 years
              Message 6 of 10 , Sep 7, 2012
                --- In midatlanticretro@yahoogroups.com, "Bill Sudbrink" <wh.sudbrink@...> wrote:
                >
                > LCD display also survived. The "repair" ended up taking almost an entire
                > frustrating weekend. It was my wife's computer. Initial evaluation:

                Ouch, that must have been very frustrating! The guys down at the store must be thinking "You again?". Well, this would be one of those things in 20 years you can look back at and laugh (if you're not laughing, add another 20 years).

                > (Oh, I guess the speaker survived too)

                Oh, that's good, that saved you $0.50 for a new speaker. (Sarcasm never comes through in email)
                I guess that was a weekend of "what can go wrong next?". I've had my share of bad repairs, but not that bad. Well, chaulk it up to experience.

                Cheers,
                Josh
              • joshbensadon
                ... Are you saying the transistors in the old analog computers are robust? I haven t looked at part numbers yet, but they look like the old germanium TO-05
                Message 7 of 10 , Sep 7, 2012
                  --- In midatlanticretro@yahoogroups.com, David Gesswein <djg@...> wrote:
                  >
                  > You can look up a couple of the part #'s to see the breakdown voltage.
                  > Since the analog computers weren't normally trying to use the fastest
                  > transistors they may have a good margin on breakdown voltage.
                  >

                  Are you saying the transistors in the old analog computers are robust? I haven't looked at part numbers yet, but they look like the old germanium TO-05 case style. I have zero experience in Analog computers, I would love to pick someone's brains on them. New thread?

                  Cheers,
                  Josh
                • s100doctor
                  Bill described what appears to be a catastrophic failure of a 21st century personal computer s power supply, that apparently took all the other components with
                  Message 8 of 10 , Sep 8, 2012
                    Bill described what appears to be a catastrophic failure of a 21st century personal computer's power supply, that apparently took all the other components with it, drives and video cards and of course the "motherboard".

                    David Gesswein addressed some issues of analog computers which used discrete transistors (as opposed to vacuum tubes, for example).

                    But the original question was about crow-bar circuits on power supplies, or tantalum capacitor failures.

                    My point in calling this sequence out, is that I caution against trying to draw broad conclusions from very specific kinds of repair problems, component failures, and types of design - conclusions across different eras of personal computers. I think broad conclusions and comparisons are not productive. and even harmful.

                    Without posting a lecture about it......I think it's more reasonable to focus a discussion of computer repairs, to a fairly specific class of computers - specific time and place, models, designs - than to go off to talk about a five-year old computer failure in the same thread as 40-year-old transistors in an analog computer. It's like talking about an engine breakdown from an oil leak in a 2009 Toyota Camery, in the same discussion as a head gasket leak in a Model T Ford engine. Those are good discussions, but not the SAME discussion, in my informed opinion; what you learn from one won't help much with the other.

                    Herb Johnson
                    retrotechnology.com
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