Paul wrote:

> In terms of what is broken, that is still uncertain in my mind. The
> motherboard
> could be the problem (driver not working on the PS_ON# line). Another
> test for
> the power supply, would be to disconnect the main connector from the
> motherboard,
> and see if PS_ON# is pulled up to +5V or not. If PS_ON# was still 2.7V,
> I might
> suspect the power supply. The supply should not run with the main connector
> unplugged, as the PS_ON# should be pulled up to the inactive +5V logic
> state.

Not totally accurate. The PS_ON signal level is TTL compatible. There is a
voltage divider of sorts in most PSUs, not just a pull-up to +5vsb. 2.7v is
fine for a TTL high signal, which should keep the PSU off. Anything less than
0.8v is low enough to turn PSU on.

> You can continue to run it with a manual switch if you want. The +5VSB
> supply
> has limited current flow, and even if there was an issue between the +5VSB
> supply and the PS_ON# signal, no more than a couple amps can flow.

The current that the PS_ON circuit can provide is limited by the same resistor
that is part of the pull-up voltage divider, normally at least 1K ohm. So
we're talking about milliamps here, at most.