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Power to LED backstrips but not lighting

I have tested LED strips and all light up. I test them with led tested an both line test out at 100v and all come on. When plugged into the power board I am getting 180 to the 1st + and 90 to the 2nd but still will not light up. I have changed out both the power board and the main board. I get flashing standby light and see image with flashlight test, yet still mo backlights

Update (02/19/2021)

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Hi @green68j,

Try the following:

Turn off the TV if it is on and disconnect the power from the TV.

Remove the back cover from the TV and disconnect the cable between the power board and the mainboard.

Reconnect the power to the TV.

The TV backlights should turn on full intensity and stay on. There will be no images on the screen because the mainboard is disconnected.

If they turn on and stay on then there is a problem with the mainboard or the cable or cable connections between the mainboard and the power board.

Check the voltages at the connector where the mainboard cable was connected to to see if they’re as per what is shown on the power board.

Be safety aware as there is exposed lethal AC voltage on the power board

If they blink or don’t turn on then there is a problem with the power board or the connection between the power board and the LED strips

Disconnect the power from the TV and then disconnect the LED power cable from the power board. Reconnect the power to the TV and then measure the voltage at the LED power connector on the power board between each of the +VLED pins and earth. The voltage should read >220V DC. If there is this amount of voltage then there is a problem from the LED power cable to the LEDs or a faulty connection between the LED power cable and the power board

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I disconnected mainboard and still no backlights. I turned of the power plugged the main board back in

I then plugged back in and check power to the LED power and got a reading of 180vDC on first +VLED and 80vDC on the +VLED. I then unplugged the power and unplugged the LED. I plugged the power back in and check the voltage. On the 1st +VLED I got 180vDC and on the 2nd +VLED I got 0vDC.

I got these same results with 1st new powerbord so I got a new mainboard and still the same. So I then got another new powerboard and it's still the same.

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Also the mainboard seems to be getting the proper voltage but it gets really hot

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@green68j

180V on the power lead to the LEDs should be enough to turn them on.

Also with disconnecting the LED power cable to voltage should have ramped up but maybe this TV is different to other Samsungs in that it doesn't if there is no load connected to it.

Where did you prove that the LEDs were working from, the LED power cable plug that connects to the power board or at the LED strips?

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I did it from both. From the power board connection each line with the LED tester would read 100v and each set of 3 strips per would light up.

I also took everything apart and tested each individual strip and they all lit up.

So when I give them direct power with the LED tester in anyway possible they would light up. I just can not get them to light when plugged into the boards.

This is my frustration

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@green68j

What's the power board's board number?

Perhaps a schematic for it can be found.

Also have you checked that there is a good earth connection to the boards?

Just wondering and again it may be different with your model, usually testing the LED voltage is done between the +VLED and an earth point on the board i.e. a screwhead and the boards should all be connected via the metal back of the TV so that they all have the same earth and one is not "floating" above earth potential which can cause problems.

Just scratching as to what the problem may be.

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