When I look at the picture here, I see a 24 pin main connector, and a
2x2 ATX12V connector for processor power.
http://ae.asus.com/999/images/products/2341/2341_l.jpg
The four pins on the end of a 24 pin connector, have four
different colored wires. The wires carry redundant 3.3V, 5V, 12V1,
and GND.
http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf
What purpose do redundant wires serve ? They increase the ampacity of the
interconnect. Each pin of the connector, can safely handle 6 amps of
current flow (the exact number may depend on the gauge of wire leading
to the pin). There are five red wires in the 24 pin wiring harness,
which all carry +5V. 5 wires times 6 amps each, gives 30 amps maximum
that the motherboard could draw, without burning the connector. In
practice, a motherboard designer would likely try to avoid going
all the way to 30A, since the current sharing in a motherboard
isn't perfect. (Some pins carry more current than others. One
motherboard I checked, the spread is +/- 1 amp.)
The most important pin of the new ones, is the extra 12V1 pin. Since
the 24 pin connector now has two wires carrying 12V1, up to 12A can
be drawn from that rail. On your motherboard, there is one video card
slot, and the most slot power I've heard of in a video card slot,
was a load of 4.35A. So 4.35 amps doesn't exceed the single wire on
a 20 pin connector. There could be an issue if two video cards were
present, as 2*4.35 = 8.7A, and then you would benefit from the use of
a 24 pin connector.
*******
In terms of power supply shorting, there are a couple cases to consider.
The motherboard could have a (partial) short, between a rail and ground.
That would strain the power supply, and bring it close to its limits,
causing it to heat up internally. Or, if the overcurrent detection in the
supply
was actually working, it might shut off the supply, at about 30% over
its rating.
A second kind of fault, would be rail to rail. Say the +5V rail on the
motherboard, had a partial short to 3.3V. Current from +5V would flow
into the 3.3V rail. The ATX power supply is not "push-pull" and has
no way to compensate for that. The 3.3V rail voltage will rise, the
feedback system will hit the wall, the supply will make its maximum
possible correction to the disturbance, but the 3.3V will still be
rising. If the power supply is well equipped, it will have OVP. The
supply will shut off, if the 3.3V rises high enough. If it doesn't
have OVP, then perhaps the motherboard components will be fried
by the out of spec voltage.
*******
When a motherboard pops two supplies, either the calculation of
required power is wrong, or the system is drawing more power than
it should be. To check that, you can use a clamp-on DC ammeter.
(I have the 380947, in this document.)
http://www.extech.com/instrument/products/310_399/datasheets/380941_942_947.pdf
To use it, I place the five red wires in the ATX power supply
bundle, all within the jaws of the meter. Set the meter to 40A DC
max range, then take a measurement. The meter sums the magnetic
field around the five wires, so is able to measure the combined
current flow. In that way, I can determine whether the loading
is "normal" or not.
If I take the meter, and clamp it around an AC cord, it reads zero,
because the magnetic field around the two power carrying conductors
cancels. To measure AC power, you need a "cheater" cord, where the
outer insulation of the cord is removed, leaving the three insulated
wires inside loose. By grabbing the hot wire, and clamping around
that, it is possible to make an AC measurement. I have a couple
cheater cords I made myself, as I'm too cheap to buy one from the
meter company.
I've also used that meter to work on the car. When my car was having
trouble starting on a cold morning, I used that meter to measure the
peak current consumed, and it measured 150A on the 400A DC scale. So the
meter can be used for more than just motherboards. I also use it
for checking the current draw on the central air conditioner. (The
fan on my central air, draws twice the rated current, and some day,
it is going to burn out.)
Is it worth investing money in a specialized meter like that ?
Probably not. But it does have the advantage, of allowing a
"non-contact" method of measuring current. No fuses to pop, no
accidents. Inside the device, is a Hall probe, which is what
converts the magnetic field into a voltage. The jaw design
is a flux concentrator, that helps the device only measure
the magnetic field encircled by the jaws. Fields outside
the jaws are ignored.
http://en.wikipedia.org/wiki/Hall_probe
To make a current measurement with a conventional multimeter,
would require
1) Measure individual wires, one at a time, due to the 10 amp
limit of the highest range on a cheap multimeter.
2) Purchase a 24 pin to 24 pin extension cable, and chop each
wire in two, then insert the multimeter between the two
ends, then turn on the computer and make a measurement,
while the computer is running your favorite test case
(Prime95 perhaps).
So it is possible to make some measurements, but by measuring
the individual wires, there could be additional measurement
error. And with that many wires, I'd probably buy crimp terminals
and a terminal block, to make it easier to manage all the
cut ends of the wires.
To measure currents over 10 amps, you can make your own shunt
out of manganin wire. You have to set the shunt resistance low
enough, such that the manganin doesn't get too hot. Manganin
is selected for its low temperature coefficient of resistance,
which is why it would be preferably to using some nichrome wire
scavenged from your toaster.
http://en.wikipedia.org/wiki/Manganin
A Hall probe based meter, avoids some of those issues, and
makes it much quicker to measure system power consumption
on a per rail basis.
