What would cause a computer to simply stop?

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The major components are a Gigabyte mobo, Antec Earthwatts 380 watt
PSU, 2.33 gig Core2 Duo, XP Pro, 320 gig WD Caviar PATA C: drive, 320
gig WD Caviar SATA aux drive.

After replacing some bad ram a couple of days ago, the machine was
running like the proverbial Swiss watch until today when it suddenly
winked off. Just quit as if it were unplugged. This has never happened
before. I tried turning the PSU switch off and on, tried disconnecting
the PSU main board connect and reconnecting. All that would happen
would be that if I turned off the PSU switch for a minute, turned it
back on, hit the ON button, the case fans would nudge briefly and then

Took the PSU out, took it to the local computer shop, they said it
tested good.

Put the PSU back in, hooked up enough components to make the machine
run, still nothing other than the aforementioned case fan nudge.

Took out the C: drive, stuck it in another machne, it fired right up,
no problems.

Put the C: drive back into original machine (that was exhibiting the
symptoms) and now it does fire up. Hmmm....

Only thing is, after a few minutes of browsing the machine winks out
again -but- this time it spontaneously reboots.

Anoter thing I noticed is that with the aux SATA drive disconnected
the C: drive wasn't showing up in bios, even though XP was coming up.
Admittedly, I didn't change the jumper on the C: drive after
disconnectng the SATA drive. When I reconnected the SATA drive, both
were recognized in bios.

After all this, any theories as to what might be going on?

Thanks for all input.

Re: What would cause a computer to simply stop?

Doc wrote:
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OK. Let's review.

You've been inside the machine. You changed RAM.

Occasionally, a stick of RAM will have a bad capacitor or a sloppy solder
joint, and "stuff burns". Since your computer was running like a Swiss Watch
after the install, that probably isn't it. Generally, when that happens
(infrequently), it happens to brand new product, at first switch-on.

You may have bumped something while in the PC.

Verify the ATX 12V 2x2 power connector is firmly in place.

Check that the CPU heatsink/fan is making good contact with the CPU,
and that the fan is spinning. Set the fan to maximum speed (i.e. if
it is currently under Automatic Control, set it to manual and let the
fan have full 12V). Now, try the machine again, and see if extra
cooling effort helps.

A computer will wink off, if THERMTRIP is triggered on a CPU overheat.

But your computer rebooted, rather than just shutting down.

Rebooting suggests you next check for bad capacitors around the CPU socket.
Check the aluminum cylinders with plastic sleeves. The top of each, should
be flat. On electrolytics at least, there are pressure relief seams. If
they burst, electrolyte leaks out. The power circuit the cap is part of,
them becomes unstable and spontaneous reboots can happen.

A number of newer Gigabyte motherboards, use Polymer caps, rather than
electrolytic, and then the motherboard bad cap theory is out the window.

The same thing can happen inside the power supply (bad caps). They don't use
Polymer caps in the power supply, so it's always a candidate for analysis.

If the power supply is under warranty, opening the lid voids the warranty.
A sticker will usually cover one of the four screws on top. If it is outside
the warranty period, remove the four screws that hold on the top of it.
Have a look for bad caps. (You're looking for orange goo, as shown. This
power supply is bad, and looks very similar to my failed, older model Antec.)


If you entirely remove the power supply from the PC, then connect
the ends of a paper clip between PS_ON# and an adjacent COM pin,
you can turn on the supply. The shop says it tested good. We could
either take their word for it, or test it again. I use a load
box for that, which places a light load on the supply If it ran for
a couple hours, without complaint, with a 100W load on it, I'd probably
pass it.

If you don't have a load box, have no interest in building one, then
the next best thing is to purchase a spare power supply and install it.
I try to keep a 500W around for fun and games. If I have my suspicions,
I pop it in for a trial. Since power supplies are always failing,
you'll be using the spare, sooner or later...

Another thing - take a look and verify the power supply fan is still
turning, and that the power supply is being cooled.


Re: What would cause a computer to simply stop?

On 3/22/2011 10:06 PM, Paul wrote:

  I use a load
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Hey Paul

Care to tell how to build a load box?

Re: What would cause a computer to simply stop?

TVeblen wrote:
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Blast from the past :-)


Now, when I built mine, I was able to get an ATX connector shell and crimp pins
at a local electronics store. Since then, another store offered an ATX
extension cable for sale at a reasonable price, and if you chop that up, it's
a better starting material, because you get a prewired connector (no crimping
needed). Just strip the wires and solder the resistors to it.

One of the enthusiast sites built a "real one", with banana plug holes so you
adjust the load on each rail. If you have, say four resistors in parallel, you
set them up such that external wires are used to connect them to the load. A
load box
you might have in a lab, would likely have a rotary switch to switch in various
bu it's too hard to find rotary switches. The banana plug route is more crude,
and still
costs a fortune to put together.

Mine is a fixed load, and not a stress test. If I had a power supply with leaky
perhaps I could connect it, and see if the thing "stays up" for any period of

At the factory, some of the load testing is dynamic, such as load dump tests or
the like.
There are specifications on the ATX supply, for how long it should take to
respond to
a dynamic event, but the static load boxes I'm talking about, aren't designed
for that.

My load box is mainly to protect me from an "infant failure" on an ATX supply.
I get a new supply, I put it on the load box for two hours, and check the rails
a multimeter. That isn't a guarantee all is well, but intended to weed out a
supply damaged in transit.


Re: What would cause a computer to simply stop?

On 3/23/2011 1:21 PM, Paul wrote:
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Thanks Paul
A fun weekend project!

Re: What would cause a computer to simply stop?

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My guess is a ps not supplying enough amperage on the +12V rail.

What video card are you using?

I ran into a similar problem with a system with a 500W power supply,
and a NVIDIA GeForce 9600 GT card.

The card specs called for a minimum of 26 amps on the +12V rail, while
the ps only provided 24.  The system would reboot with no apparent
reason.   The clue that it was a ps problem (leading me to find the
card's specs) was that the system wouldn't even boot with three usb
devices connected.  Any 2 of the three were ok, but all three, no way.

Replacing the ps with a 750W unit that was rated for 52 amps on the +12V
rail cured the problem.

Regards, Dave Hodgins

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Re: What would cause a computer to simply stop?

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NVidia GeForce 8600.

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I've wondered if this 380 watt is a bit marginal for this system but
haven't encountered this particular problem before in the over year
I've had the machine.

Since getting it up and running again it hasn't done it again....so
far. Have done some video capture and processing.

Re: What would cause a computer to simply stop?

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The machine I ran into the problem with ran for about 3 months, with
occasional spontaneous reboots, with no obvious cause.

The problem being related to the power supply became clear when I
added a third usb device, (parallel port interface), after which
the system wouldn't boot.  With any two of the three usb devices
connected, it would boot ok.  With all three, it wouldn't.

Replacing the ps with a 750W unit, that provided up to 52A on the
+12V rail fixed the problem.

Regards, Dave Hodgins

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use in usenet. Feel free to use it yourself.)

Re: What would cause a computer to simply stop?

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Antec is a good name, although 380W does tend toward yesterday's power
supply ratings.  Among present offerings, I'd consider 500W closer to
an entry point for average wattages, well in advance of 380 and
possibly 500.  Doesn't hold up technically speaking, though -- 380W,
if you're built not to exceed that then you should be fine.  I just
like being in the present tense when it comes to who's buying what
over a widest range of distribution for comparative satisfaction.  A
brand name may also loose some of their weight if I'm working off
reviews for prices.  Last time I experienced something similar, I was
able to reproduce the problem from issues I found with mounting my
original build work, that I needed more care for mounting the MB
mating to the case.  Grounding issues, iow.  Then again, I have
replaced the PS with better if not newer units, successfully
addressing issues.  If I'm not entirely certain of a PS build quality,
I start watching for sales on well-reviewed units for either a backup,
on principle no less handy to have around as spare monitor.  Or, just
as apt to be a change-out for preventative maintenance, if the new
unit turns out to be built significantly better.  Everything else,
memory, video cards, motherboards -- have been relatively rare problem
instances compared to power supplies.

Re: What would cause a computer to simply stop?

Doc wrote:
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My guess is you jimmied a cable.  Unplug and reset each of them, taking care
to notice that each wire in each harness is locked in place, and engaging
its counterpart.

I had a HDD molex connected that was loose (the female barrel connector was
to large), and any vibration would park the heads and reboot the box.  I
fixed it by reducing the diameter of the female barrel slightly with a pair
of hemostats, and it fixed the problem.

Good luck.


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