Have a few corona boards, at least one of the v2 and a v4 that only beep when buttons are pressed. They are virgin boards. Checked the obvious USB pins, checked U5A1 and U5A2 and the reliability header for proper voltages. I have read that U1B1 can be an issue so I checked that and the voltages do not match up. I replaced the mosfet with one from a working board and still get the same readings. Place the "bad" mosfet on the working board and it works fine. So I have eliminated the fet as an issue. Does anyone have any experience with this issue?