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- Power supply hell
March 11, 2006, 3:03 pm
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I need some help on a problem that just kicked my butt. It's not exactly
on-topic, but it did all begin on a pc with a Sempron that I'd hoped to OC.
I don't think all the specs and details are necessary for this particular
issue. But I'll be happy to provide all of it if it will help.
Anyway, a friend's computer (Emachines) started getting flaky. The
integrated usb and sound died, but the computer was still running okay. I
put usb and sound cards in, and all seemed fine. My thoughts were to work
around what I perceived as a dying motherboard until we could get in a mobo
with a decent oc'able bios. So I got the pc to limp along and I ordered a
mobo. After a day of running the computer, it started acting funny again -
a random reboot, hanging up, etc. "No huge deal," I thought. The new mobo
will be here in a day or two. When we brought the pc back over here the
night before, I turned it on and something popped - not real loud, but
noticeable. I didn't see or smell any smoke or burning. Then the pc would
not power on. I grabbed a working power supply, plugged it in - still
nothing. "Well, that mobo finally bit the dust." No big deal, I knew it
was dying anyway, and the new mobo would arrive in the morning.
The new mobo did arrive. I put it in, hooked everything up, and before I
even turned on the power, smoke began emanating from the I/O chip. Again,
the power was not on, but the power supply was plugged in. It was a budget
PC Chips mobo (~$40 usd) - by no means top of the line. "Damn quality
control!" So I ordered another mobo. When it arrived, I was scared to plug
it in. Part of me was starting to suspect the power supply. I've seen some
bizarre things with Bestec's in budget PCs. So I hooked up an old broken
mobo to the Bestec. Sure enough, it fried a chip or two on the mobo before
I even turned it on. So I put a good psu in the Emachines, installed the
replacement mobo, and it's running better than ever.
So I picked up the Bestec, held it by arms length, and set it over in the
corner. When I look at it I sometimes see Chuckie from the horror movies
staring back at me, waiting for me to plug him into another unsuspecting
What is up with that Bestec power supply? Is it throwing a dc spike or
something? And could I have seen it coming? How could I have tested for
this - had it crossed my mind, given the original observations? In other
words, where the hell did I go wrong.
Please take it easy on me. It was bad couple of day.
Re: Power supply hell
There is some info on building your own power supply tester here.
My last two builds, I tested the power supply for two hours or
so with that circuit.
The idea is to load the power supply, with a load representative
of an average motherboard. Some of the AthlonXP motherboards
that ran the processor from +5V, had quite different characteristics
than the ones that use +12V for the processor. And now that
there are ATX 2.0+ supplies, with split +12V outputs, you need
another resistor load added to test the extra output. So the
values calculated for the P4C800-E would be a starting point,
but noting that with the more modern supplies, the motherboard
+12V load has dropped (maybe 3 amps load on the 24 pin connector),
while the ATX12V 2x2 connector current has more load (10 amps
for a high end processor).
Once the power supply load is built, you connect it, switch on
the supply (by connecting PS_ON to an adjacent COM pin), and
all voltages should appear. Then, using a cheap voltmeter, you
can measure all the voltages at the loads, and see if they are
within 5% of the correct value.
I expect your +5VSB is way high on the Bestec, and perhaps that
is why it is frying motherboards. Using a voltmeter will tell
you whats up.
Note that, there are these cheesy dongle style testers for
sale, but at most they load only one rail, and would not be
putting a representative load on the power supply. That is
why I built my own test load - cheaper to use rugged resistors,
than to keep destroying motherboards. Expecially if you are in
While you can turn the power supply on, without a complicated
load, the voltages you see may not be representative of the
regulating capabilities of the supply. Some minimum load is
required on some of them, to "pull" them into spec. But, if
the +5VSB on your supply is responsible for frying the motherboards,
you can in fact, plug in and turn on the supply, and just look
at the +5VSB, to see where the voltage is resting. That would
be without using a shunt from PS_ON# to COM. The +5VSB starts
to run, when the switch on the back of the supply is put in
the ON position, and that is enough to be able to see if the
+5VSB is in spec. So you don't need to turn the supply
all the way on (with the PS_ON# to COM connection), to check
Re: Power supply hell
I just made the same mistake a few days ago. I bought my Gigabyte board
which had some ide driver issues. Shortly after I noticed that my computer
was getting slower, especially on shutdown. I then started getting a snowy
moniter and eventually the computer wouldn't even boot. Because of previous
MB problems, I bought a A8N-SLI Deluxe and rebuilt the system and again no
boot. With the asus, my computer did make continuous 5 short quick beeps.
Fortunatly, a buddy living next door was an A+ guy and said the beeps meant
power supply problem. So I removed my bad Thermaltake 420 watt and replaced
it with a $65 350 watt and my computer is working better now than it ever
did in the 2-3 years I had the thermaltake. I think it was bad right out of
the box. I'm going to switch to Enermax shortly.
Re: Power supply hell
I use a 500 watt Enermax liberty modular power supply with an Asus A8N-SLI
premium motherboard, works like a charm! You'll be happy with it, and
they're NOT overly expensive either!!
Enermax Liberty 550
2 GB OCZ PC3200
Seagate Baracuda 300 GB SATA II
XFX 7800 GTX 256