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Repair and disassembly information for the Samsung 55" UHD television with model numbers UN55MU6290xxxx. Released in 2017.

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TV will not turn on, no standby light

My samsung UN49MU6290 TV will not power on and will not show a standby light. I replaced both the power board and the main board. When I disconnect the cable going from the power board to the main board then the backlights will turn on. I checked the voltage from the power supply and the chart says it needs to be 12V and when I have it disconnected from the main board it will show the correct 12v but when I have it connected to the main board it shows 9v. I am not sure what to do next.

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Hi,

Just wondering if you have the correct chart as one of the voltages you quoted seemed wrong.

Searching for a Samsung UN49MU6290FXZA power board, shows that the power board is a BN44-00807F. On the board it shows that the Standby voltage is 7.5V at the test point which should change to 11.8V when the TV is on.

Where were you measuring the Standby voltage?

The 9V measured with the mainboard connected may be a bit high as the mainboard needs to have the correct voltage from the power board to turn on the Standby light. The 11.8V is ~12V which may be close enough.

Did you check to see if all the voltages were actually getting to the mainboard, by measuring them at both ends of the cable? Since you have replaced both boards it may be a problem with the cable between the two boards. Just a thought.

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(click on image to enlarge for better viewing)

Apologies if the board number in your model is not the same as shown above and the voltages may be as you say.

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My power board is BN44-00807F which is the same as what you said. And my Main Board is BN94-12641M.

Ok so when I plug the tv in and I check the standby volts I am getting 9v. And when I disconnect the cable from the main board it will show 12.94v.

I am not sure if maybe one of the boards I have is bad. But when I replace these with the originals the voltage is exactly the same.

par

Hi,

Getting down to board level testing without a schematic for me makes it difficult.

Did you measure the voltages at the connector that goes to the mainboard?

Can't see if too well in the link I posted but usually the voltages for the various pins are shown next to the connector.

Normally the voltage on the Standby "pin" of the connector (if it is marked) won't change when the TV is turned on. It may change at the test point but that may not be the same point as what is connected to the STBY lead to the mainboard, perhaps just a convenient point to see if the voltage is there and if it changes when the board is turned on.

With the TV off most of the other voltages shown will not be there. When the TV is turned on the mainboard sends a signal on the PS_On wire, usually it is the pin next to the STBY pin which turns on the power board and then there should be voltages on the other pins as marked.

If you decide to test there be extremely careful as you are near high DC voltage when the board is powered on and also not far away from lethal AC voltage.

I don't know why both sets of boards would exhibit the same characteristics i.e. that the standby light doesn't turn on with power available.

I can only surmise that given the replacement boards are both OK, then whatever it is, it is common to both sets of boards

par

Alright so I first checked the stand by voltage from my last post. I went and checked the voltage on the pins from the connector and it still 13v when the power board is disconnected from the main board and it still shows 9v when they are both connected. I also tested the pins on the cable itself coming from the power board and the cable is working fine. I will attach a photo that shows the voltage chart next to the power board connector.

par

@Ryanjflo

With the power board disconnected from the mainboard all the voltages shown as 13V should have that voltage on them as usually with Samsung boards the power board is turned full on when the mainboard is disconnected from it and the power is connected to the power board.

Having 9V may be OK as I have read further that sometimes the boards can be used in other TVs and this voltage can be altered to suit, but the board designation isn't changed, but not 100% sure about this.

In any event have you checked the at the mainboard end of the cable to see if the stby voltage appears there?

If it does then since the power board seems to turn on OK as you said that the backlights also work OK when the mainboard and power aren't connected and power is applied to the TV then it is looking like there is a problem with the mainboard.

The only other thought that comes to mind and I haven't checked it out as it seems too far fetched is if that the TV button control board (or the remote??) is somehow preventing the TV from turning on. Maybe if you disconnect the control board from the mainboard or disable the remote (you have to leave one operational) and try

par

@jayeff so I checked the voltage at the main board connector and at the power board and everything seems to be reading at 9v on both ends.

I checked the voltage from the cable itself and everything read fine aswell.

I also disconnected both the wifi module board and the control board and I even tried to disable the remote but still nothing turned on.

I assume that I am not having any problems with my Power board since the backlight turned on and the voltages seem to be correct.

I will try and get a replacement main board sent out and try again. It is strange that this will now be my 3rd main board so hopefully this will work. Thank you

par

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