Have a great day,
As I guess you see that ATX power supplier is not on when there is blackout for more than just a few seconds. It is an ATX power supply feature. If you look into RDB schematics you can see that ATX POWER INPUT CONNECTOR has PS-ON pin driven by PWR_EN_N signal from transistor (Q30) controlled by D-trigger (U84). The ATX power supply is ON when PS-ON pin is low.
Unfortunately I do not simple way to pull PS-ON to ground (some board has jumper for that). It seems we need for some hardware changing.
As you can see after blackout D trigger keeps PS-ON high until you press the button which provides clock edge to the D trigger which changes its state. I think we can remove resistor which connects the D-trigger Q output to the transistor. Instead we add the resistor to connect it to the Q# the D-trigger. In this case the power should be provided without button pushing because Q# is high while the Q is low. But the button still can switch power off and on.
Serguei
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