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- Asus Motherboard Problems
February 27, 2006, 3:35 am
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the status light on the board keeps flashing green whenever i geive it
power. However, it will not turn on, no fans or anything come on.
THe first thought that came to my mind was "bad PSU"...this was because
there is a faint buzzing that the PSU emits that is in synch with the
flashing led on the motherboard. But with firther troubleshooting, i
ruled out a bad power supply by shorting 2 pins on the 24-pin connector
which turned everything that was hooked up to the PSU on, but not the
Mobo because it was disconnected.
So now i am stuck and wondering what i could do. The online retailer
(newegg) will not accept it as a return because it is past the initial
30-day period. Asus tech help is kind of flaky, and the search on thier
forum doesnt even work.
So i was wondering is anybody had any good ideas to try and also
whether or not ASUS has any type of warrant on thier motherboards. ANy
info would be helpfull.
Re: Asus Motherboard Problems
That "flashing status light" is telling you something.
That green LED is powered directly from +5VSB and is not
driven by any logic. The fact that it is flashing, tells
you the +5VSB is failing on your power supply. The LED
should be lit steady, or turned off. There is no valid
state where that motherboard LED is allowed to flash.
It means the power supply is turning on and off rapidly.
Either the PSU is bad, or the motherboard or something
else is overloading the supply. If this was my motherboard,
I would pull the motherboard out of the computer case, and
assemble the system on a table top. (Select a work area,
where no one will play with your stuff. It is easy for
someone to pull a component out of place, so find a quiet
place to work, with a lockable door on it.)
The purpose of pulling the motherboard out of the computer
case, is to check that nothing is shorting to the bottom
of the motherboard. I place the motherboard on top of a
thick phone book, with a cardboard cover. And that is why
it is called the "cardboard test". The only dangerous part
of this test, is the video card is not secured to the
motherboard, so be very careful not to tug on any cables
while working on it. (Also remember to unplug the
computer, before adding or removing components. That
helps ensure no +5VSB derived voltages are present on
If the system still behaves the same way, when assembled
outside the case, I would swap the power supply for another.
Next step, would be to swap the motherboard. The odds are,
that it is the fault of the power supply.
If this is a tiny supply, it could just be too small for the
job. The 300W supplies that come with computer cases, are not
necessarily big enough to run just any hardware configuration.
There are some web sites that can help you work out the needed
power, but the one I like (takaman) still seems to be down
for some reason, and perhaps it is gone for good.
If you cannot find someone to work out the power required for
you, then a 450W supply will _probably_ be enough. Generally
speaking, using the wattage rating like that is pretty stupid,
but without your hardware details, it is the simplest advice
I can give. A much better way, is to work out the power
required for the 3.3V, 5V, and 12V outputs, then select
a supply based on the answer.
If you have a spare supply handy, a short cut would be to
install it in place of your current supply and try it. If
things are more stable, then you know for sure it is the
PSU that is faulty.
Re: Asus Motherboard Problems
have already determined that the PSU works fine.
THe exact process i followed to determine this was to:
-remove the 24 pin connector from the motherboard, but leave everything
else plugged in.
-i then took a peper clip and shorted the 13th and 14th wires on the 24
-this resulted in everything turning on (except for the motherboard
obviosly)...the hard drives even booted.
so this leaves me wondering what is wrong with the motherboard. The PSU
i have is a 500watt PSU, so underpowering is not a problem. My
motherboard documentations contanains nothing about a blinking green
LED and i have not been able to find any info on the web (forum posts,
so i am still confused.
Re: Asus Motherboard Problems
So you know the power supply works with a partial load on it.
You still don't know if the power supply works with a full load.
You could connect the (suspect) supply to a known working
computer. And see if it can power that computer. That
computer will be closer to a full load. (Especially if you
were to run Prime95 or CPUburn on the computer, once it is
booted into Windows.) If the suspect supply cannot run a
second computer, then the odds are the PSU is at fault.
To see how a power supply works, the author of this web page
has traced the circuit of an ATX supply and drawn a schematic.
If you've ever tried to trace a circuit yourself, you'd realize
just how impressive this work is. It takes a person with an iron
will to do something like this. And the effort is much appreciated.
In that example design, the +5VSB (bottom left of page) is an
independent switching circuit. The only protection I see in
that circuit, is the 78L05 has an internal thermal overload
(part of the IC and would not be shown in a schematic).
I don't see a protection on the primary side. And in that
design, I don't really see a good mechanism to make the
"status LED" to flash at a high rate. The thermal protection
would have to cool off, and that should take some time (there
would be hysteresis).
A loss of primary energy (300VDC from rectifiers) could make
the +5VSB wink out, but again, there is no failure mechanism to
account for the flashing. Note - If the supply was plugged to 115V
wall outlet, and the switch on the supply was set to 230V, that
might do it (as the rectifier would be running in half wave mode).
Be very careful with that switch! (The combination of a 230V
wall plug and a 115V switch setting will yield a loud bang, so
be sure you know what you are doing. Unplug the computer before
fooling with it.)
In any case, if you don't have a lot of test gear, you'll be
swapping hardware sooner or later. Pick your favorite
culprit and replace it.