M789 power loss restart - the solution is very easy!
spirit at reactor.ru
Thu Oct 21 06:48:01 CEST 2004
I think, this can be put onto the FAQ.
I found the solution that works for M789 and is very easy and cheap.
It also must be a universal solution, helping to power-up any ATX
motherboard on power up of the PSU.
Just take a small capacitor (i used a 2uF one) and put it in
parallel with the standard power button on your case. Or just
connect the capacitor to the PWR BTN header on the motherboard.
This is much easier and cheaper than using any digital solution
(with a counter IC or anything). The principle behind my solution is
that upon powering up the PSU, the 5VSB line becomes high on the
motherboard. That line powers the circuitry needed to react to the
power button. Additionally, voltage appears on one of the pins of
the PWR BTN header on the mobo (the other pin is ground). So, when
there is a capacitor between the pins, it starts charging. That
looks like a short circuit to the mobo. It boots up. The capacitor
becomes fully charged and it starts looking like an open circuit to
the motherboard. The capacitor is never discharged while the mobo is
powered and is discharged quickly after the power is removed.
Additionally, the functionality of the power button is preserved -
you can still push it to turn the PC off.
In other words, the capacitor is equal to "AC Power Loss restart:
Always On" setting in the BIOS.
WBR, Alexander mailto:spirit at reactor.ru
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