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'[OT] How best to test a computer power supply'
2008\01\27@130431 by Lindy Mayfield

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One of my older servers just died.  How can I check to see if it is the power supply?
I know that sticking my multimeter into the wires probably won't tell me because if I understand correctly it needs to be under a load.  Could I bend the wires of a resisiter, clip my multimeter onto them and then plug the ends into the power supply plugs?  If that would work, what value resistor would I use?
Thanks,
Lindy


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2008\01\27@132059 by Neil Cherry

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Lindy Mayfield wrote:
> One of my older servers just died.  How can I check to see if it is the
> power supply?
>
> I know that sticking my multimeter into the wires probably won't tell me
> because if I understand correctly it needs to be under a load.  Could I
> bend the wires of a resisiter, clip my multimeter onto them and then plug
> the ends into the power supply plugs?  If that would work, what value
> resistor would I use?

Old disk drives are good for this but you may also need to have a
connection on power-good. I'm not sure if it's 5v or 3.3v now. I
*THINK* it's just a short to your 5v line.

A better option is to get a power supply checker. My friend has
one an we use it all the time.

--
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2008\01\27@152159 by Matt Pobursky

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On Sun, 27 Jan 2008 18:59:59 +0100, Lindy Mayfield wrote:
> One of my older servers just died.  How can I check to see if it is the
> power supply?
>
> I know that sticking my multimeter into the wires probably won't tell me
> because if I understand correctly it needs to be under a load.  Could I
> bend the wires of a resisiter, clip my multimeter onto them and then plug
> the ends into the power supply plugs?  If that would work, what value
> resistor would I use?
>
> Thanks,
> Lindy

Neil Cherry is right, get a PC power supply tester. It will provide
sufficient loads and power on signal to test the supply. The better ones
will also test most all the rest of your power carrying cables in a PC (PCI
Express, SATA, floppy, HD, etc.). They aren't expensive and even if you
only use it once in a while, it's worth it's weight in gold.

Here are a few links to some I'd consider:

www.virtual-hideout.net/articles/psu_tester_shootout/index4.shtml
(I have this one and it works well)

http://www.mwave.com/mwave/skusearch.hmx?SCriteria=BA21965&CartID=done&nextloc=

http://www.pcper.com/article.php?aid=246

Which reminds me, I have a stack of PSUs accumulated in my lab that need to
be checked out. ;-)

Matt Pobursky
Maximum Performance Systems

2008\01\27@170257 by peter green

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> Neil Cherry is right, get a PC power supply tester. It will provide
> sufficient loads and power on signal to test the supply. The better ones
> will also test most all the rest of your power carrying cables in a PC (PCI
> Express, SATA, floppy, HD, etc.). They aren't expensive and even if you
> only use it once in a while, it's worth it's weight in gold.
>
>  
The downside of those devices seems to be that their loads are fixed. To
thorougly test a power supply you need to test it with both the stated
minimum and stated maximum load on each rail. I also wonder whether
those testers can say whether the voltages on a rail are in spec and
clean or if they can only give an indication of whether they exist at all.

2008\01\27@170549 by Clint Sharp

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In message <2008127142134.868027@Phoenix>, Matt Pobursky
<.....piclistKILLspamspam@spam@mps-design.com> writes
>Neil Cherry is right, get a PC power supply tester. It will provide
>sufficient loads and power on signal to test the supply. The better ones
>will also test most all the rest of your power carrying cables in a PC (PCI
>Express, SATA, floppy, HD, etc.). They aren't expensive and even if you
>only use it once in a while, it's worth it's weight in gold.
 I'd just temporarily swap in a standard ATX PSU from a desktop system,
if it's not ATX compatible then the majority of cheap PSU testers aren't
going to be suitable either. Neil's wrong about power good, it's an
output from the PSU.
>
>Here are a few links to some I'd consider:
If Lindy had let us know what the server was then it would be easier to
make recommendations.
--
Clint Sharp

2008\01\27@172920 by Dario Greggio

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Clint Sharp wrote:

>>Neil Cherry is right, get a PC power supply tester. It will provide
>>sufficient loads and power on signal to test the supply. The better ones
>>will also test most all the rest of your power carrying cables in a PC (PCI
>>Express, SATA, floppy, HD, etc.). They aren't expensive and even if you
>>only use it once in a while, it's worth it's weight in gold.
>
>   I'd just temporarily swap in a standard ATX PSU from a desktop system,
> if it's not ATX compatible then the majority of cheap PSU testers aren't
> going to be suitable either. Neil's wrong about power good, it's an
> output from the PSU.

I'd do the same: with the current price of those PSU, it'd be my first
choice to check.
Even if it was not suitable to power the whole server, it can at least
be used to determine if the older one has failed. And then the "real"
one can be purchased and swapped into.

--
Ciao, Dario -- ADPM Synthesis sas -- http://www.adpm.tk

2008\01\27@173346 by Neil Cherry

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Clint Sharp wrote:

> going to be suitable either. Neil's wrong about power good, it's an
> output from the PSU.

Oops, I stand corrected.

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2008\01\27@180240 by William \Chops\ Westfield

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On Jan 27, 2008, at 2:02 PM, peter green wrote:

> To thorougly test a power supply you need to test it with both the  
> stated minimum and stated maximum load on each rail.

heh.  While this is theoretically true, I think testing a typical  
consumer computer power supply at its stated maximum load is just  
asking for trouble...  (and even if it's accurately rated, aren't  
there weird co-dependencies between 5V and 3V, or similar?)

BillW

2008\01\27@200543 by SM Ling

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>
> One of my older servers just died.  How can I check to see if it is the
> power supply (PS)?


Did it show symptom like difficult to start? can't power more USB? or it has
clocked at least 1.5 year continuous running hour?  If so, chance is very
high that it is the PS.

Test with the a new PS, or test the suspect PS on a known good board?

I came across old intel server that startup circuit was problematic also.
To test this, I simulated the PON (power on) signal to the PS to see if the
PS turns on - the PS fan was a good indicator.

Cheers, Ling SM

2008\01\27@221244 by Matt Pobursky

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On Sun, 27 Jan 2008 22:02:34 +0000, peter green wrote:
>
>> Neil Cherry is right, get a PC power supply tester. It will provide
>> sufficient loads and power on signal to test the supply. The better
>> ones will also test most all the rest of your power carrying cables in
>> a PC (PCI Express, SATA, floppy, HD, etc.). They aren't expensive and
>> even if you only use it once in a while, it's worth it's weight in gold.
>>
>>
> The downside of those devices seems to be that their loads are fixed. To
> thorougly test a power supply you need to test it with both the stated
> minimum and stated maximum load on each rail. I also wonder whether those
> testers can say whether the voltages on a rail are in spec and clean or
> if they can only give an indication of whether they exist at all.

The one I've got puts a load of a few amps on each rail. Most supplies
(ATX) made in the last 5 years or so have fairly relaxed minimum load
requirements but I'm reasonably sure anything more than an amp or two of
load current on each rail would meet any minimum requirements. My tester
also has a window comparator on the rails as it's flagged both high and low
spec. rails as bad.

Of course it's not a thorough test at upper output current limits, noise
specs. etc. It's meant to supply a moderate load simultaneously with a
power on signal so you can do a quick go/no-go test and quickly eliminate
an obviously bad supply or power cable. It works well enough for that.

Also, most people don't have 300-500W worth of test loads laying around
their workbenches for full load testing. ;- )

Matt Pobursky
Maximum Performance Systems

2008\01\28@010218 by Herbert Graf

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On Sun, 2008-01-27 at 18:59 +0100, Lindy Mayfield wrote:
> One of my older servers just died.  How can I check to see if it is the power supply?
>  
> I know that sticking my multimeter into the wires probably won't tell me because if I understand correctly it needs to be under a load.  Could I bend the wires of a resisiter, clip my multimeter onto them and then plug the ends into the power supply plugs?  If that would work, what value resistor would I use?

Assuming it's ATX, short the green wire to ground. Most supplies no
longer need a load to operate correctly. To be sure a HDD is a perfect
load.

TTYL

2008\01\28@115553 by M. Adam Davis

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One of the PC enthusiast websites took it upon themselves to do a real
load test across a range of PC power supplies.

It turns out that ALL of the PC supplies dropped their power good
signal before reaching their rated output.  Most of them recovered
when the load was lowered, but one actually failed completely and was
unusable thereafter.

Good ATX supplies follow Intel's spec, which includes several
interesting requirements.  Failing power supplies must not emit flame
or smoke (bad smells ok, but not visible smoke).  Failing power
supplies must not damage the load (ie, crowbar type protection
required).

I've never had a PC power supply fail and destroy the PC.  (I've had
several where an external event destroyed both such as lightning, but
never the supply's failure itself).

So, all that being said, a simple power supply tester with minimal
load will be useful, but power supplies are cheap and unless you have
a good reason not to you should always replace the supply if you think
it's a problem.

Even good PC power supplies degrade quickly over time, and the
quickest way to figure out whether the PS is the problem is to connect
a new one.

If you really want to test it first, and prefer not to buy a tester,
then place 2W loads on 3.3V, 5V, and 12V lines (most power supplies
are regulated at either the 3.3v or 5v output and all other outputs
are relative to the main regulation, so you might only need one load).
Then short the power on pin to ground and check the output and power
good signal.  If power good does not become active then the power
supply is bad regardless of the voltage output.  If power good is
active, and the votlages look good under the small load then you can
be reasonably certain the power supply is good.  The power good pin is
actually quite picky - I don't usually test for it, but when I have
I've never seen a bad power supply output active power good.

-Adam

On 1/27/08, William Chops Westfield <.....westfwKILLspamspam.....mac.com> wrote:
{Quote hidden}

> -

2008\01\28@121925 by Lindy Mayfield

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It is just something I put together from individual parts from a small
computer store in Heidelberg.  Generic case with power supply,
motherboard, disks, CD, etc.

-----Original Message-----
From: EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu [piclist-bouncesspamspam_OUTmit.edu] On Behalf
Of Clint Sharp
Sent: 28. tammikuuta 2008 0:05
To: Microcontroller discussion list - Public.
Subject: Re: [OT] How best to test a computer power supply

If Lindy had let us know what the server was then it would be easier to
make recommendations.
--
Clint Sharp

2008\01\28@132625 by Lindy Mayfield

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It's about 5 or 6 years old and I brought it out of the closet to run
Linux. It ran continuously for some months and then one day it was just
dead.  When I hit the power button, the front panel led comes on for
just a second and makes a very light "fsss" sound, which I cannot place.


I'll check out the PSU checker.  It'll be good to have in my box of
stuff.

Thanks to you and all who answered.

-Lindy

{Original Message removed}

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