ATX motherboards: early power-on circuitry?

[Whales]

I have a cute little passive atom x86 board out of a piece of proprietary rack equipment.  I want to use it as a small computer but it won't turn on.

No useful make or model markings.  I suspect part of the proprietary wiring harness is needed to turn it on, but I don't have any of that.

The LPC chip gets quite warm (Nuvoton NCT6776F) and one 5V rail + some 3.3 appears (the unit only takes a single 12V input).  None of the main power supplies (eg for the CPU) turn on.  No sounds, squeals, lights or jolts as I short any of the pins labelled as FRONT_PANEL (looks like the same 9-pins of 2.54 that you get on desktop boards).

Q1: How is early-turn on handled on ATX motherboards?  Is the power switch header wired directly to a power supervision chip, does the LPC handle it, etc?

Q2: Any public ATX motherboard schematics or info that I can learn from?
 

[Whales]

Buzzed out what I thought was the front panel sw pin & found it went to pin PSIN# on the LPC chip.  Hooray, I always start getting somewhere just I as I need to get to bed for work tomorrow

Any and all advice appreciated.

[coromonadalix]

post photos of your atom board, any brand or markings ?

[fzabkar]

Identify the ground pins in the 9-pin header.

Apply power and determine which pin(s) have a standby supply, eg 5VSB or 3.3VSB.

Determine if any of the standby supply pins are actually pulled up to a standby supply via a resistor. This will probably be the Power_on pin.

Short this pin to ground, either momentarily, or by holding it for a few seconds as you would a normal desktop PC.

[magic]

I once had a bad PSU which didn't assert the POWER_GOOD signal and the board just sat quiet and kept waiting for it.

[Whales]

Thanks for the tips.

It turns out the LPC is very well documented in a public datasheet, complete with logic gates/requirements for boot signals.  Going to hunt these signals out one by one.