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Samsung UN40H6203AFXZA 40” LED TV – no backlight

I was watching TV last night, and the picture suddenly went black but the audio remained working.  The “flashlight test” shows the image IS on the screen – so I assume backlight is not working.  Why?

I took off back panel to have a look.  I unplugged connection between power board and main board and turned the TV on – the backlights did NOT light.  I powered down and then reconnected the main board.

See images below for boards.  The power connector going to the LED strips has the pins layout labeled as shown below, with voltages I measured:

Pin       label     Volts

1          D1+      209

2          D2+      202

3          D3+      192

4          NC        0 (no connection)

5          D1-       202

6          D2-       192

7          D3-       0

With no voltage on pin 7, does that indicate the problem is with the power board, or the LED strips?  How does one differentiate/correctly diagnose between these two potential causes?

Thank you,

Kurt

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Hi @probro968 ,

How did you take the measurements? Did you have the DMM connected between earth and the D+ve leads? The D-ve leads are the return path for the current.

Did you measure the LED voltages with the LED power cable still connected to the power board or disconnected from the power board?

Try measuring the voltages at the power board LED power cable connector point, with the LED power cable disconnected from the power board and check the voltage on all the D+ leads only. They all should be a high voltage as there is no current flowing through the LEDs.

If this is the case then the problem is with the LED strips or the connection to the LED strips as the power board is trying to drive the voltage as high as possible in an attempt to turn on the LEDs

Here’s a video that may help

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Hello Jayeff, thank you for helping.

I took the voltage measurements reported in my OP with the ground touching the chasis, and the positive touching the denoted pin on the connector on the power board. The cable was indeed connected to the board at the time.

I just now did as you instructed and removed the cable, powered on the TV and measured the voltages at the D+ leads only. Results:

D1+ 208

D2+ 0

D3+ 0

From your statements I am guessing my problem is with the power supply?

Kurt

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@probro968

Definitely looks like it as there are 3 feeds going to the LEDs and they should all have power.

I would have thought that one section of LEDs would be on but maybe not.

If you had access to a LED backlight tester (examples only) that would definitely prove them as well

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