"Rob" said:
I was hoping someone could help me, I have a PC that keeps powering off at
different times, but what I don't understand, is the only way to restart the
PC, is by turning the Power Supply Switch Off then back on, if I try to
restart it with the Power Button on the PC it won't do anything, but once I
turn the switch on and off on the Power Supply, Then I can start it up,
using the power button on the PC..I have no over heating problems, in which
I have checked and did a MEMTEST86 no bad memory, it just shuts off whether
its 1hr, 24 hrs or 5 mins..
Has Anyone heard of this?
Windows XP Pro
AMD 1.6MHZ
Thanks for any help...
Rob
(e-mail address removed)
You don't say what kind of processor you've got, but many motherboards
have a "thermal trip" circuit. It either originates inside the
processor, or in the case of AthlonXP, a small circuit on the
motherboard can implement that kind of protection.
A second protection circuit, can be in the processor's Vcore circuit.
Many of those circuits will have overcurrent detection, and it is designed
to "latch". That means, as soon as the overcurrent condition happens,
the circuit shuts off, and it _may_ require removing +5VSB from the board
(pull cord, or use the mains switch on the back of the computer)
to get it to recover. Normally, the motherboard manual will not
explain what to expect when it happens, so there is no way
for the end user to know (there should really be a LED on the
motherboard that lights up when this happens).
I would inspect the motherboard with a strong work light. Examine the
capacitors (cylinders with a plastic sleeve on them). The top of the
caps have lines stamped in them, and the lines form a pressure
relief point (so the caps don't explode). If a cap is failing, either
the top will bulge, the top will crack open, or brown juice will
leak out the bottom and onto the motherboard. When the cap is failed
like that, it can form a conduction path and draw current that would
normally not flow. If the motherboard did not have overcurrent
protection in the Vcore circuit, eventually it would be bad enough
that a MOSFET or one of the coils would get burned up. In extreme
cases, the area all around the processor socket will roast and the
PCB material will be discolored by the high heat.
ATX power supplies also have protection like this. At least the
good ones do.
So, you have power supply or motherboard as possible suspects.
A bad processor could also load down Vcore, but that would
be the last thing I'd swap out. A power supply is the most likely
to fail. Bad caps on a motherboard are mainly an issue with
a certain era of motherboards, and some brands seemed to use
more of the bad caps than others. For example, this web site
was set up, after the settlement of a class action lawsuit.
http://www.abitsettlement.com/
You can see some caps in the foreground here:
http://www.motherboardrepair.com/images/BadCaps3.jpg
("Homey", from the Abit group, repairs bad caps -
http://www.motherboardrepair.com )
Knowing the brand and model of motherboard would help. Or
simply running your brand and model number through Google,
will tell you whether "capacitor" is an issue with your
type of board.
Paul
