TV backlight powers on when plugged in, but unresponsive

Thanks for your response @jayjeff!

The model number is un55eh6000fxza and the power board I believe is BN44-00499A. I have already tried disconnecting the main board and powering on - backlights come on same as before. I believe my next step is to test the standby power, but I'm not sure where it is on this board.

I have located the STBY voltage on my other TV power board (that will be a separate question) but I cannot find it on this one.

@jeffthewhiteguy

Looking at this image of the board (hover your mouse over image to zoom in) I can't see it either, but check what the PS-On/Off voltage is on CNM803 pin 14 (bottom left corner of image).

Also check the 13V and 5V supplies values on the same connector.

With the mainboard cable connected it will be difficult but with it disconnected the power board should be turned on as you have the backlights so the signal is missing on PS_On/Off coming FROM the mainboard.

You may have to remove the power board and follow the tracks to where CNM 803 pin 14 goes to that will allow you to connect your meter more easily so that when you reconnect the mainboard cable to the power board so you can measure what the PS_On/Off voltage is with the mainboard connected but the TV not turned on. if it is the same then there is a problem in the power board.

I can't find a schematic for the board so proving which component is faulty will be difficult.

@jayeff I'm a total novice when it comes to checking voltages, but I tried my best to check the connector from the power board to the main board. Assuming that pin 1 is the top left, pin 2 is bottom left, and so on... I got the following voltages:

1) 13.03 2) 3.45

3) 13.03 4) 13.04

5) 13.04 6) 3.00

7) 13.03 8) 0.00

9) 0.00 10) 0.00

11) 5.36 12) 5.36

13) 5.36 14) 3.35

Voltage across the fuse was 0.05v .

I tested the board completely disconnected. I couldn't follow pin 14 on the bottom of the board, but I will try again if necessary.

@jeffthewhiteguy

You counted them correctly. Pin 1 is numbered and designated on the board with an arrowhead so it is the top left. Pin 13 is also numbered but no arrowhead All the odd numbers are along the top row and all the even numbers are on the bottom row as shown in the pinout table printed on the board near the connector.

You can easily measure the odd numbered pins with the cable inserted but not the even numbers (as long as you don't short out the pins with the meter's test probe ;-)

The 13V and 5V voltages seem to be about right, it is the value of the pin14 PS_On/Off that would be of most interest.

I'm assuming that these measurements are with the cable disconnected so it would be good to find a suitable measuring point that connects to pin 14 so that you can measure it with the cable connected to see if it changes at all. That's where having the schematic would have come in handy ;-(

My thinking is that usually the backlights come on when the cable is disconnected so there must be a control voltage coming from the mainboard to keep them off until the TV is turned on with the cable connected, because when the cable is not there they turn on i.e. no voltage.

Given that the Standby voltage is the only voltage available to the mainboard in Standby (and this is what I don't know for your model it could be either 5V or 7V as it is in other Samsung models) a control voltage of no more than either of these voltages should be there. It could also be less than those mentioned but not 0V as then the backlights should turn on as they do when the cable is not there. Hopefully you follow my reasoning.

You could always contact the supplier in the link I posted above and ask which board is the more likely problem. The worst they could do is not tell you.