Do I need a 'special' power supply for this Dell Optiplex?

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Hi All; thanks for reading!

I have a Dell Optiplex which I think needs a new power supply.  It shuts off
immediately whenever I do "certain things"* in Windows, as well as sometimes
spontaneously.  (*included for your curiosity, and the off-chance this is
actually a configuration issue of some sort:  one of the things is Windows
Security Center.  Opens fine but clicking any of the presented options
results in immediate hard shut-down.)

It is also doesn't want to power up most of the time, which, more than the
Win issues, is what makes me think it needs a PS.

It's a P4 system but I am not sure of the exact specs.  The Model tag on the
case just says "DHM".

I have done a bit of research on replacing the PS -- Dell P/N: NPS-250KB
D -- and it looks like it can be replaced fairly inexpensively, but I would
like to do some testing before just "throwing money at the problem".

I have some PSes around which could be used to test, if I was certain that
it was safe to plug them in to this system.

I have seen reference to custom wiring Dell was doing on the ATX+12V
connector and I am pretty sure this system is not of that design, but I
would like someone more experienced in these matters to confirm that, as
well as pointing out any other dangers of using a power supply other than
the official Dell model.

The system was bought used for about $100 so I am not encouraged to spend a
whole lot to figure this out.  (It belongs to my father and I am billing him
at a reduced rate...                   J/K - it's pro bono, of course!)

Any insight would be appreciated.  Thank you!


Re: Do I need a 'special' power supply for this Dell Optiplex?

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  I don't see anything that points to a power supply.  I see symptoms
that point to many things as suspects.  How to confirm power supply
integrity or identify it as a suspect in but two minutes: "When your
computer dies without warning....."  starting 6 Feb 2007 in the
newsgroup  at:

  Meanwhile, this same test can also identify a failing computer
before it fails. If you must replace the power supply, then repeat the
procedure to confirm that new supply is stable - will not cause
failures in two months.

  Kony has provided a picture for how that connector is wired - if it
is a standard ATX power supply.  Wires listed in that procedure are
the wires in:

  With a meter and using those three limit numbers in that procedure,
then know it is a good or bad supply - or even if the supply is
overloaded.  Once a power supply is known good, then move on to the
other hardware solutions.  But if you do not first confirm power
supply 'system' integrity, then those other problems may be created by
a power supply.

Re: Do I need a 'special' power supply for this Dell Optiplex?

trs51x wrote:
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Usually there is some kind of model number, to go with the "Optiplex" name.
That might make it easier to see what info is available on the Dell site. You
might get lucky, and find actual confirmation that the thing uses ATX wiring,
or has some slight differences. (Generally, suppliers of replacement parts,
will not tell you these details, because then you wouldn't be stuck doing
business with them :-) )

To test if it is a power problem, I might try a program like Prime95 (or
any other program known to load the processor to 100%). I would start the
Prime95 program and see whether it shuts down as soon as you start the
"Torture Test" in Prime95. If it passes Prime95, the next thing I'd try
is a benchmark like 3DMark2001SE build 330, as that stresses both the video
card and the processor, and would draw even more current from the power

I also might look for a program which can display temperatures and voltages.
Something like Speedfan or MBM5, if they will work with your computer.
You should be able to run the temperature display, at the same time
as you run Prime95.

Your computer could be shutting down due to processor overheat.

It could be shutting down because the PSU has detected an internal problem.

And if you suspected a software problem of some kind, you could get a
Linux "live" distro like Knoppix or Ubuntu, and try booting and using
them. Both of those distributions, are available on a self-booting CD,
and you don't even need a hard drive connected to the computer, for
a live distro to be able to boot. Once in Linux, you could use the
Linux version of Prime95, to again load up the processor. (To make your
own CD, both distributions are a 700MB download.) The idea here, is by
using Linux, you are completely shed of Windows and whatever
virus/trojan/driver problem you might have.

So there are a few experiments you could try first, before tearing out the
power supply. If you go to , you can undoubtedly find
a nice substitute supply for the one you've got.


Re: Do I need a 'special' power supply for this Dell Optiplex?


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Best (cheapest) way to find out for sure: download a CD that runs
on the PC without using Windows.
E.g. Memtest86 or Knoppix.
(Knoppix is better, because it lets you actually use the entire
PC without being dependant on Windows.)

That way, you can see if the problems are caused by some hardware
malfunction or by Windows acting up.

One other warning: most PSUs are exchangable, but Dell has some
models that use different wiring (on the very same plug).
So: unless you are very sure you have the right PSU, never just
switch PSUs if the label says Dell !

Kind regards,
Gerard Bok

Re: Do I need a 'special' power supply for this Dell Optiplex?

On Tue, 27 Mar 2007 17:51:18 -0400, "trs51x"

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I would ignore this for the time being, it might be a
separate windows problem.  If you have the restart-on-error
setting in XP enabled, try disabling that.

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Yes, this is more telling, though if you have a lot of
things hooked up to USB, try unplugging those temporarily,
unplugging the system for a minute or two, then plugging
back in and trying it without the USB things connected.  If
this helps you might have too much powered by the 5VSB rail
of the PSU, and would either need to unplug some of it, or
find out if some USB ports have a jumper to select 5VSB or
5V rail, or use a powered USB hub for some of the USB

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Has the system been upgraded, as far as you can tell?  I'm
wondering if the 250W PSU ought to be upgraded to something
a little stronger, like a decent name-brand 350W or so, at
least 18A on 12V rail rating.

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Maybe, see items mentioned below.  Also if these PSU are
older, be sure they have ample 12V capacity else they might
lead to a false conclusion, being inadequate for the system.

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If the alternate PSU puts out the right voltages on the
right connectors, and is reasonably designed, at worst if it
was of insufficient capacity it should just refuse to start
or shut off.  Compare the present PSU to one that is
standard as mentioned below.

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Open the system and note 3 things:

1)  The dimensions of the power supply.  A standard ATX is
roughly 15cm x 8.5cm on the side that mounts to the rear of
the case.  Length can vary but is usually about 14cm.  If
these measurements are off, you may have a PS3, mATX, or one
of the odd proprietary Dell PSU shapes.  If you have an odd
shape you will have to buy another Dell PSU. has a few of those odd ones,
they might have it cheaper than some places.

2)  The pinout of the main motherboard connector.  Compare
to this picture, at least for the first 10 rows of pins if
it is a 24 pin connector.  If a color deviates, check
voltage with a multimeter if you can, or at least see if the
placement of the different color still remains constant to
the same pin positions.

3)  Whether there are any other connectors going to the
motherboard.  It would be standard to have a 2x2, 4 pin
connector supplying 12V for the CPU, but you might have
another connector or something different.

Some other rarities might include a 3VSB from the PSU - if
it is present it would be listed on the PSU label, and would
not be available on a standard ATX replacement PSU.

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