I've cleaned this board up after some minor corrosion. Replaced U2890 and anything around it that looked bad. Board has 3V3_LDO and PP3V3_G3H. I can't see anything else that would keep it from getting 20V but it's now just cycling between 5V and nothing on the USB input. Screen goes blank and then goes to 5V with no current. Any idea what this might be telling me? I'm stuck as far as a next move.