Bai Gu your Klein tool will not work for this. You do need to get a simple multimeter (analog or digital will work) You need to measure the voltages on CN6401 of your power board and see which ones are present. Those are DC voltages. You need to have the STBY voltage. If you do not have that, it is your power board that is having problems. There is also a reason why this power board seems to be very difficult to come by. It is common that boards that are widely unavailable are those that are having a high failure rate. The xbr-75x850G can use the xbr-75x850F power supply.