Hello Robert.

>>   I would suspect however it to be an open-collector output.
> It is.

> And for many motherboards, putting a jumper on the 'pwr sw' pins
> asserts this signal permanently so you don't have to go about pulling
> pins out of the power cable. RTM!

  A manual with that amount of detail is in my experience (of the
cheaper motherboards, by and large :) a bit of a rarity.

  Now the power switch is in fact a toggle, but with no facility AFAIK
for "repeat", so I daresay in this circumstance the toggle logic sees it
at (true) power-up and toggles ON, then stays that way.  OK.

  I have/ had (sitting behind me as I speak, went "phut"!) a MB with
that very behaviour now I come to think of it.  Started when you power
up, but power switch did not work.

  What is *bad* about it, is that when Windoze powers down the ATX, you
then have to pull the power plug and put it back in to make the thing
power up *next time*.

  I think this transaction is worth the list's attention ;-)
--
  Cheers,
        Paul B.