Sorry for the late reply.

I ordered a new mainboard and it works perfectly fine.

Thank you everyone for helping me diagnosing the problem. ...

I tried pressing down on the CPU,EMMC, and the two RAM ICs while pressing the power button, did not help sadly. I will try the compressed air trick you meantioned on monday however.

First I try pressing down on the ICs and If it doesn't help I proceed to rewrite the SPI as you said....

I have a CH341 programmer but I don't have the bin file for it sadly

Here is some photos of the MB and the two Winbond IC:
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Both IC has 3.3V on pin 8 right after plugging in main, and after pressing the power button too....

Turns out my multimeter probe is damaged, so after replacing it I managed to find out that both 13V and 18VAMP is present on the PSU.

So it's looks like the MB (SOC?) after all, only symptom is the periodically clicking relay in the One connect box.

EDIT: I took off the heatsink from the mainboard check it. Plugging in the system in the socket causes the SOC to become blazing hot instantly. ...

By checking I meant measuring diodes, caps, etc....

I took out the PSU and I check around on it.

Meanwhile I noticed that the standby led does this after "forcing it" to start:

VID_20251016_103047

Disconnecting the panel does not changes it....

If it's the panel, disconnecting the LCD ribbon cables should make it start no?

If It's BGA, reflowing would help it or I should get a new IC (If it's even possbile.)?...

Dear everyone I have a QE65Q8FNAT Samsung TV with one connect box.

The symptoms are the following:
- The TV has stand-by LED, pressing the power button only flashes it once, holding or pressing it multiple times makes it disappear but you can hear a faint relay click from the one box and the red standby led comes back.
- No backlight or sound comes from the TV.

I took apart the one box, suspecting it to be faulty but I couldn't find anything, but I grabbed a spare working one connect box + cable from my friend to try it. Same symptoms.

So There...