After studying this a little further I am thinking LIN_REG_EN is not making it to the 3.3V supply. The the linear regulator could show the 3.3V when the knob is pressed but if it is not being passed through to the VDD output then the processor would not be coming up.? ?Hooking up the USB could provide parasitic voltage through internal pullups, enough to turn Q110 on, but this is an unproven theory.? It does not explain why the behavior goes away though.? Another path to look at.
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Brien - KE7WB
Brien - KE7WB