01-26-2012, 06:42 PM
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 Re: Desktop Will Not Start Immediately
tb wrote:
> I have two desktops hooked up to the same power strip. After I shut
> down the PCs I also turn the power strip switch off.
Why? If the computers are powered down, the miniscule power consumed by
an ATX motherboard for the 5VSB to the power-on circuitry on the
motherboard is probably equivalent to a single bulb in a Xmas light
string. You'll waste far more power turning on the lights to take a pee
at night then leaving than your powered-down computers with live input
power would take for a month.
> When I turn the power strip switch back on, desktop A starts up
> immediately after I press its power button. For desktop B, I have to
> wait approx. one minute before pressing its power button. If I don't do
> that, computer B will simply not turn on.
When you apply power to the input side of the PSU (power supply unit) in
your computer, it will provide +5V standby to the power-on circuitry on
the motherboard. The old AT-style PSUs had a mechanical switch from the
front of the case that went directly to the PSU. This was a mechanical
switch that actually disconnected power from the PSU. In the newer ATX-
style PSUs, you don't turn off their power directly. Instead the
momentary Power switch connects to the motherboard to control its
power-on circuit which obviously needs to be powered. The PSU, when it
has power, will supply 5V to the power-on circuit. When you press the
Power switch, it shorts to ground an input in the power-on logic (pin
14, green wire, in the 20/24-pin connector from the PSU to mobo) that
then tells the PSU to bring up all its power rails.
> I can pretty much rule out a problem with the power strip or the wall
> electrical receptacle. I also have used a different power cable between
> the power strip and the computer's power supply plug.
>
> Since I know absolutely zero about electronics, I am turning to this NG
> for ideas as to what could be wrong with desktop B. What would be the
> most probable cause that prevents desktop B from turning on after I
> switch the power strip on and immediately press the PC's power button?
>
> The motherboard is MSI Eclipse SLI X58. Despite being an SLI
> motherboard, I only have one Radeon HD 4850 512MB installed. I have 6GB
> of memory and an Intel i7-920 microprocessor. The power supply is a
> Seasonic 400W.
>
> Up till two weeks ago I did not have this problem and the PC is only
> about three years old...
I don't know if this is one of them but some mobos will not power up
with a dead CMOS battery. There is a capacitor in the circuit so maybe
it needs to charge when power is first applied or restored. Replace the
CMOS battery and retest. Although rated to last 5 years, that's when
they are newly manufactured, not after some storage time after
manufacture, shipping time to a distributor, more storage time in
someone's stock, and then shelf time at the store or shop before placed
into use plus the computer was built awhile before you bought it (you
didn't say you built the computer). Figure on 3 years for the lifespan
of a coin cell battery included with a pre-built computer which is how
old is your computer, so replace it with a new one rated for 5 years of
use from now (and replace in 3 years) and retest.
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