820-00165 (25mA with a quick flash of 100mA) Flying Blind!

[KC Micro Tronix]

This board is Tricky for me. The flash of 100mA is caused by the brief 1/10 sec turn on of U3900. U3900 is on for just a split second and no thermal signatures out of the normal are detected.
PP3V3_S0 is never present during this cycle.
25 Mhz clock is present
3V3 enable flashes but only to 0.5v along the same time line as U3900.

I feel like a newbie asking for help on this board. But I am flat stuck.

 

[2informaticos]

Diode mode to ground on 3V3_S0 rail?
Check for pulse with o-scope.
It can also show if enable signal reaches 3V peak...