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21069Re: Need 3B2/310 Help!

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  • epsilonprocess
    May 3, 2011
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      --- In midatlanticretro@yahoogroups.com, Mr Ian Primus <ian_primus@...>
      wrote:
      >
      > --- On Tue, 5/3/11, epsilonprocess als@... wrote:
      >
      > > The cover was on when it started smoking, so the smoke I
      > > saw came out of the floppy drive opening but I can't be sure
      > > it was the floppy that was the issue. What I might do is try
      > > to fire up the floppy drive using a standard ATX supply to
      > > see if it still works.
      >
      > I'm going to doubt there is actually a problem with the floppy drive
      itself. More than likely, that was just a convenient exit for the smoke.
      >

      That's what I was thinking. I'll give it a quick test at some point.


      > > However, I did find where there was OBVIOUS damage on the
      > > system board power supply connector. While I can't be 100%
      > > certain this wasn't there before, I would go with the fact
      > > that it happened as a result of whatever caused the smoke.
      > > Unfortunately, I can't find any sign of a short...yet,
      > > anyway.
      > >
      > > See photo: http://home.prog.fm/3b2-ps1.jpg
      >
      > That's odd - and it's not burned in the way that connectors like this
      usually fail. It's almost as if something conductive fell there and
      burned away.
      >

      The red connector that has all the wires is undamaged. The white
      connector on the board itself took all the damage and there's some
      bubbling underneath on the PCB. Not sure if the traces are broken. I'll
      have to test with a meter.


      > > What I found odd was that measuring the resistance between
      > > the red wire bundle and the blue (or ground) there is only
      > > 20ohms of resistance, while measuring the yellow bundle to
      > > blue (or ground) is almost an open. Is that normal even
      > > though I got a clean +12v and +5v? Oh and, I measured while
      > > the system board power was still connected BEFORE I noticed
      > > the damaged connector.
      > >
      > > I also didn't see any obvious caps blown on the power
      > > supply. Where is the square cap located approximately?
      >
      > It should be fairly near the power input. These caps of which I speak
      are AC line safety capacitors. They're this clearish yellow color, and
      look a bit like a board mount relay. When they fail, they fail shorted,
      and blow open, spewing TONS of smoke - and they tend to fail the first
      time a machine has been powered on in a long time. I'm not even 100%
      sure that power supply has them, it's just that your description of the
      failure sounds so much like what I've seen in several other machines.
      >

      I'll take a closer look, but I didn't see any damage on the power supply
      itself. That's the first place I looked. Would the power supply even
      work and give anything close to +5 and +12 volts with that cap blown?


      > Now, you say you get clean +5 and +12... does the computer work? Does
      the power LED come on? The diagnostic LED should come on until it's
      finished with it's internal self test, which it won't pass if the
      battery is flat.
      >
      > That burn on the board is odd. Have you checked between the power pins
      on that connector for shorts on the board? Also, if you have been
      testing the power supply unloaded (disconnected from the board and
      drives), you might be getting false readings. If there is something
      wrong with the power supply, it's possible to have it put out the right
      voltages (or nearly right), until you put a load on it, at which point,
      it goes into shutdown. I usually use a couple of junk PC IDE hard drives
      as a load - plug the power connectors in and turn on the supply, and the
      drives should spin up, then check your voltages.
      >

      I took the readings with the floppy and hard drive disconnected, but
      with the system board connected. I didn't see the damage on the
      connector until I dismantled the system board/expansion cage, but there
      was no further smoking. I did later plug in the hard drive with the
      system board disconnected, and it did spin up, though I didn't take any
      readings with it connected. I'll have to do that.

      With the system board connected, the green LED lights up. If the reset
      button is pressed, the green LED flashes then goes solid again. There's
      only a red LED next to the green one that I figured was the hard disk.
      Is that the diagnostic LED? If so, that one never lit up. Also, the
      rocker switch on the power supply has "diagnostic" position that
      doesn't seem to do anything. The power supply only seems to work in the
      "on" position. Is it supposed to do anything in "diagnostic" ?

      At no point did the system POST anything to the terminal. It's a 610
      terminal set to 9600/8/n/1. I didn't check the battery level. I'll have
      to do that as well. Hopefully, I'll get a chance to get to the shop
      tonight or this week. Let you know what else I find.

      Thanks,

      Anthony
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