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Hi, I have a Samsung TV UN40MU6300FXZA that stopped working. When I unplug the wire harness between the power supply and main board, the backlights turn on. So I thought it would be the main board, so I replaced it. The tv still did not work and I still have NO standby light. I get voltage at the power supply but thought maybe I am missing something so I replaced power supply too since it wasn’t expensive. Still nothing. I verified that serial numbers of boards replaced match those of the OEM boards. Any idea what else could be wrong? There does not seem to be much more I can replace. I have power to all other connections; power button, speakers, even the wifi block. Thank you in advance.
Up close image of standby/ON pwr (BN44-00806F)
Hi @scudsquad , Have you checked that the standby reference voltage is getting from the power board to the mainboard, you didn’t say? It is the mainboard that turns on the red standby power LED when it receives the correct standby voltage from the power board. I realize that you have replaced both boards so maybe the problem is with the cable between them or maybe you got a faulty replacement board. It can happen sometimes The standby voltage reference point and value can be found on the power board. Here’s an image taken from a BN44-00806A power board which shows where the standby voltage ref. point is and its value. In this case it is a jumper link. The board number was found when searching for a UN40MU6300FXZA power board, so presumably yours is the same. If not then it should be similarly shown somewhere on the board.
(click on image to enlarge for better viewing) Also usually there is a table printed on the power board showing the other supply voltage values and their pin number on the mainboard- power board cable connector. With the mainboard cable disconnected from the power board and power connected to the TV the backlights should turn on as you said but the power board is also turned full on so that you can measure all the voltages that it supplies to the mainboard to see if they are all OK. It is better to measure voltages first before replacing any boards as this can give an indication of where the problem most likely is Be safety aware when testing for voltages on the power board. Even though the standby voltage is low DC voltage there is still exposed lethal AC voltage on the power board and close to where you are testing. Notice the “hot” and “cold” dividing line on the board
