Sometimes dead standby on Philips 75PUS8505

Hi everybody,

I have 75PUS8505 and trying to solve issue with TV. TV is out of warranty (have it from brand new,approx 3,5y and have 8849 working hours) Time by time standby LED turned off (TV looks dead,does not do anything when press any button on TV or remote) but power cycle solved always this problem. Now power cycle wont help. Only maybe 1 of 20 tries work and power LED gets on, then TV works normally as usual. I want to figure out if is problem with powerboard or mainboard. Tried to measure voltages from powerboard to MB (have voltages in every situation, I can send if somebody can help me), but I have no clue if they are okay or not. In the TV is also last update, but dead standby LED happend also on older versions. With service menu there is "no errors" message. When TV gets standby LED on, and turn TV on, there are 2 green LEDs on MB.

2nd problem which I dont understand is - after opening TV stopped working ambilight. Nothing broken while opening, nothing disconnected. When was TV succesfully powered on I tried to turn off/on ambilight feature, also tried factory default, but ambilight is still off. Maybe this problem is connected to main problem. But firstly I want to sort out which hardware causes "dead" TV symptom.

Thanks for reply