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Powerpacks, 240 vrs 220V and output voltages

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    Powerpacks, 240 vrs 220V and output voltages

    Hi guys,

    I have a mystery here and would like some comments from those far more technically astute than I.
    Our mains voltage here is 240V. I have one Atari 800XL with a powerpack designed for 240v. Everything is fine with this machine.

    I received another Atari 800XL a long while ago as a parts machine. It was sold as condition unknown and a powerpack that the seller said didn’t work. When it arrived, I plugged it in and sure enough, nothing. However I then used my good powerpack on this machine. It went into the diagnostic routine and showed a RAM fault. Some of you might remember this, I managed to replace identify the IC and replace it with a 4164 chip. I concluded the powerpack that came with this machine was indeed faulty and consigned it to the junk corner.

    Anyway, today I was going through the junk pile and came across the old non-working powerpack. I decided to measure the voltages on this, and compare them to the working one. I expected to find zero volts on the non-working pack but instead found 7.6V. So there was voltage coming out of that non-working one after all. The label said it should be 5V but I felt 7.6 was within tolerance levels especially as there was no load. Hmm…I tested the working powerpack for comparison and this said 5.4.?

    I decided to plug the non-working powerpack into the (now working) Atari it originally came with. Nothing. I then plugged the "working" powerpack in. The machine booted but…to a black screen?? What?? I had it working on that machine with that powerpack earlier in the day and it was going fine??. Anyway, to cut a long story short, I did some fault finding and found ANOTHER RAM chip had blown, actually the one right next to the one I’d replaced.

    It’s unusual for two RAM chips to have blown just like that, so I have a theory. It was zapped by this non-working powerpack…the one putting out 7.6 volts. Remember, this was the powerpack that came with this machine, and the machine had a blown RAM IC when it arrived. Coincidence? Maybe, but I’d be interested in what you think.

    Now, these powerpacks are made for Atari 800XLs but by different manufactures and maybe for different markets. Here is a photo of the labels of both.


    The working one, is the one on the right. Made for 240v. The non-working (or RAM zapper one) is the one on the left. Made for 220V, a voltage more common in Continental Europe.
    I can’t get into the powerpack so I can’t examine the innards. Two questions though:

    1. Is a powerpack designed for 220V likely to put out a higher voltage when used on a 240V line. In other words, perhaps it’s just have to use 220v.

    2. Does an extra 2.4V really make that much of a difference? The answer would seem yes, as not only did the machine fail to fire AT ALL at this higher voltage, it also seemed to zap a RAM IC?

    Anyway, I’d be interested in your comments.

    Last edited by tezza; July 18, 2010, 01:29 PM.
    My vintage collection:
    My vintage activities blog:
    Twitter: @classiccomputNZ ; YouTube Videos: (click here)

    There are all kinds of power adapters. Some are regulated and
    others are not.
    The fact that your working one has 5.4V would lead me to believe
    that it is a regulated output.
    The 7.5V would indicate that the regulator is shorted.
    For a regulated supply, the input voltage difference between
    220 and 240 is less than 10%. This should all be within the
    range that a regulated supply could handle as an input.
    In any case, don't plug that bad one into your machines any
    more without repairing it.
    Most are sealed units but a little extra with a chissel and hammer
    will open then up. After repairs, some model glue and they are
    as good a new.


      Thanks Dwight,

      Sounds plausible. I'll have a go at cracking open the case

      I'm not familiar with the innards of a power pack though and wouldn't know what I was suppose to looking for/at. What does the regulator look like? Can you point me to some docs or give me a hint as to what I should see or test once I'm inside?

      My vintage collection:
      My vintage activities blog:
      Twitter: @classiccomputNZ ; YouTube Videos: (click here)


        Though they all look different, this is a typical 7805 regulator:

        The one you are looking for might be bigger to let more voltage through, as this one is 5V.
        The ancients knew *more* than us... They're baaaack!

        Come and see for all your gaming needs! We have Zero-ohm resistors!


          Originally posted by NathanAllan View Post
          Though they all look different, this is a typical 7805 regulator:

          The one you are looking for might be bigger to let more voltage through, as this one is 5V.
          Thanks for that. 5v is what is suppose to be output so I'll look for something similar.
          My vintage collection:
          My vintage activities blog:
          Twitter: @classiccomputNZ ; YouTube Videos: (click here)


            Just to wrap up this adventure...

            I broke into the case with hammer and chisel as suggested. It was sealed really tight hence was a mission.

            Once inside I discovered all the electronics coated/embedded in a cheese-like cube-shaped sarcophagus of green waxy material. Obviously this had been poured over everything when the case was sealed.

            This being the case, I flagged the project and the green cheese cube was binned. I retained the Atari 800XL power input DIN and leads. I guess if I ever found a powerpack of similar specs I could always wire it up to the leads coming from the DIN.

            Thanks for the feedback anyway.

            My vintage collection:
            My vintage activities blog:
            Twitter: @classiccomputNZ ; YouTube Videos: (click here)


              I always like to close these threads I started with an article on what I did and what I learnt from the experience. For anyone whose interested, here it is:

              My vintage collection:
              My vintage activities blog:
              Twitter: @classiccomputNZ ; YouTube Videos: (click here)


                Potted in resin--I really hate those!

                5V regulated wall-wart switching supplies are fortunately very easy to find nowadays. So, replacing the one on your 800XL should be simple and cheap.
                Reach me: vcfblackhole _at_ protonmail dot com.