I have this same device with the same symptoms. Applying pressure to the chip (heat sink) solved the issue.
Put a piece of foam or a folded paper between the heat sink and the case to ‘solve’ this issue.. or RMA the device.
http://forum.mikrotik.com/t/wap-r-2nd-board-dead/123105/1
Video: https://youtu.be/WTYEZuuX-CU