Re: Help! My PC won't switch on.

Mortimer wrote:
"PeeGee" <triessuk@xxxxxxxxxxx> wrote in message news:fdqu41$c87$1@xxxxxxxxxxx
Dead CMOS battery, probably not a problem as the system will probably start and the BIOS identify this problem. A *low* CMOS battery is very likely to give these symptoms (I have seen it quite a few times) and the fact that the system starts after a few minutes reinforces this as being the likely cause (as the 5vsby "charges" the battery). In some instances I have seen a PC auto-start (ABIT AX5 M/B) after a few minutes of applying power to the PSU when the battery is in this condition.

So you're saying that a low/dead/missing CMOS battery can in some way prevent the power switch from sending the wake-up signal to the PSU? Doesn't the 5V sby signal provide all the power that the BIOS needs, with CMOS battery only being needed when the PSU is unplugged from the mains? Or are you saying that a low battery will sink enough current from the 5V sby that it doesn't rise high enough for the momentary drop to 0V to be detected when the power switch is pressed?



Only a low battery, generally sufficient to retain the CMOS values, but too low to support the clock (which stops during the off period). I do not know the reason why, but I do know that what I described is the visible effect (seen on a dozen or so M/Bs). Also, having got the system started and after running for a few minutes, it will restart OK after shutting down, switching off at the wall socket for a short period, turning the power back on and pressing the power button.

A dead(very low)/missing CMOS battery just starts with CMOS errors, so removing the battery (or removing the CMOS link) is a sufficient test for this problem.

PeeGee
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