No backlighting at all, just sound
Ok, How about a picture of the rear of the chassis so I can give instructions to you, AND the model number of the TV set too.
Samsung PS43D490A1WXXU SER. B2T534PB500047N
With the back cover removed, you'll need a volt/ohmmeter aka DMM to run a short test on the plug marked with VS and GND.
Using those same test points, but with the plugs disconnected from the power supply board, you want to see if the green light blinks once a second, and your power supply board has about 200 Volts DC on the power board's VS and GND pins. Here is a picture of the tests you need to do ---
Let me know the results of those tests, because the X main may be shorted, or the Ymain is shorted. Removing the shorted board should let the power board activate and supply 200 volts DC on the Vs and GND pins on the power board. And if that's good, you should see that green light blink once a second if it's working ok.
Thank you so much for all your help, I managed to narrow it down to the Ymain board being shorted. It was a bit difficult being intermittent, but with a little bit of patience it all worked out.
Regards, ***** ***** Beer
Ps. I have ordered the Ymain board. Luckily not too expensive.