On Feb 1, 12:47*pm, Paul wrote:
mynick wrote:

thanks for great explanation
so in modern mobos the on switch grounds a pulled up line, straight to
southbridge
(Possibly there is a Schmitt trigger/inverter in between the two)

* * * * * * * +5VSB * * * * * * * * * * * * * * * * * * * * * * * +5VSB
* * * * * * * * | * * * * * * * * * * * * * * * * * * * * * * * * * *|
* * * * * * * Pullup * * * * * * * * * * * * * * * * * * * * * * * Pullup
* * * * * * * Resistor * * * * * * * * * * * * * * * * * * * * * * Resistor
* * * * * * * * | * * * * * * * * * * * * * * * * * * * PS_ON# * * * |
* * PWR * *X----+---- Motherboard logic ---- Open -------------------+- ...
* * * * * * * * * * * * * * * * * * * * * * *Collector *(to
* * GND * *X----+ * * * * * * * * * * * * * *Driver * * *ATX * * * * +
* * * * * * * * | * * * * * * * * * * * * * * * * * * * *supply) * * |
(Front * * * *GMD * * * * * * * * * * * * * * * * * * * * * * * * *GND
* Panel
* Switch)

Using an ohmmeter, between PWR and PS_ON#, doesn't tell you anything.
There is a silicon chip in the way.

* * Paul

Thanks
checked no shorts and it turned out empty bios batt prevented power
on,
however now there is no display with onboard or addon graphics
although rest seems ok(fans spinning,cpu warm,keyboard flashes)