[Luke]

Update
After some measuring i ve got some results and considerations:

J10's pin 3 4 are +5v both but with high impedance, they will go down with 220 ohm resistor, so due to the voltage level they can be considered high impedance, so they are probably a digital sensing pis, as power good or something similar, they should probably be tied down to be in the GO state. After shorting to groind it auto recover when load is removed.

J10 pin 5 is clearly the +5v stby power, it have a good strenght. It can supply at least 100mA. It goes permanently down with no auto recovery with a 25ohm load.

J11 pin 9 also is high impedance and auto recover.

Note that both connector are required to power up the unit, this can mean that the sensing and supply are on one connector and the start signal on the other.

If someone with a good unit can check and report whats going on these lines in both on and off conditions it will be of great help.