On the top Button/Power board, make sure the trace from J1p11 to the Anode of D26 is good, check D26, then make sure the trace from the Cathode of D26 to Q9p1 is good.
If all of that checks out, then the Power OK signal isn't coming from the MCU board. You'll have to start at J5p11 there and work your way back, but will most likely end up at the MCU, in which case a reflow could correct it.