ML said:
Hello
The PSU's 4-pins has 2 of the pins looked burnt. I have replaced the PSU but
still couldn't get the PC to start. The yellow LED on the MOBO is on when
power is switched on.
What are the chances that the MOBO is fried?
What else can I do?
Thank you.
The square connector, with two yellow wires and two black wires, powers
the processor. The processor does not use the power directly. There is
the "Vcore switching power converter" which is located near the processor
socket, which converts the 12V from the two yellow wires, into 1.5V
or less for the processor.
(Picture of some of the components involved in Vcore power conversion.)
http://img365.imageshack.us/img365/632/jetwayv266b1fj3.jpg
If the capacitors fail, the tops bulge and leak. That
is shown here. The tops of each cylinder should be flat.
The reason there are stamped lines in the top of the
cylinder, is for pressure release. In this case, the
pressure built up, until the stamped lines split.
Relieving the pressure before it becomes too great,
prevents accidents. Sometimes the leakage is brown or
orange in color. These are failed caps.
http://img395.imageshack.us/img395/5809/kzgexploded1hx9.jpg
If a cap fails, it can cause collateral damage. If bad enough,
it might even short the 12V feeding that circuit. That in
turn, would burn the pins on the 2x2 square connector.
The pins are rated at about 8 amps or so. To burn the
pins, you'd need to draw more than 16 amps at 12V (since
there are two pins on the yellow wires, and each takes up
to 8 amps). Connectors are rated according to power handling,
and 8 amps is about the limit for a Mini-Fit Jr connector of
that type and size. (The limit on the main connector is 6 amps,
due to so many hot pins being next to one another.) To burn
them, probably takes more current than that. (50% to 100%
more perhaps, to burn them nicely.)
So start by visually examining the components in Vcore. It
could be a leaking cylinder, a burned toroid, a burned three
tab MOSFET, and so on. Those could all be signs that the
motherboard needs repair or replacement.
Since your PC was previously working, it probably isn't a
mis-wired power supply. Since the system was working
at one time, that isn't likely to be the root cause of
the problem in this case. Some modular power supplies
(where the cable assemblies unplug), can have the wire
assembly plugged in, rotated 180 degrees. And that is
a possible cause of reversed power as well. It took the
modular power supply designers a few generations of
design, to "buy a clue" about the importance of keying.
Reversing the wires, can cause a lot of power to flow,
and will ruin the Vcore circuit.
If your system used an Intel D 805 overclocked to 4GHz,
that would be another reason for the pins to burn.
If that was your hardware configuration, you would have
mentioned that by now
Systems with that hardware and
level of overclock, draw more than 200W from Vcore.
Paul
