Samsung UE46F6400AWXXC not powering on, standby LED off

[UltimateNeutrino]

Hello, since yesterday our Samsung UE46F6400AWXXC no longer powers on, with the standby LED off. It turned off when someone attempted to clean it, not sure if related. A few days ago, there was a similar issue, but it was solved after unplugging and replugging the power. Additionally, another user of this TV reported issues of the screen turning off randomly, which were solved changing the channel.

I originally suspected the PSU, but if the mainboard is unplugged the PSU relay closes and the backlight turns on. It's only when the mainboard is connected that the relay doesn't close (no voltage on coil). Checking voltages, they seem to be normal with mainboard unplugged, but if it's plugged the only rail that works is the standby A5.3V, and for some reason the bridge rectifier output falls to about 4V. I checked for shorts in the mainboard's power connector, but I found none. I also tried unplugging the Tcon and the other boards to no avail.

Is this a mainboard issue or something else? I've seen similar models having firmware issues, but given the other symptoms, I fear it might be a panel issue.

I have attached pictures of the boards and the pinout for the mainboard power connector. Thank you in advance.

[UltimateNeutrino]

Update: I have successfully dumped the 25Q40 firmware, which I attached. Alas, it doesn't seem to match the failure pattern of other models.

[lotas]

Check on the motherboard ic202 - this is a 3.3 V S-1206B33 stabilizer. If it is faulty, check for short circuits in the submicom ic1201 Weltrend WT61P807 power supply.

[UltimateNeutrino]

Thank you for your reply, I checked IC202 and indeed, its output is shorted to ground. Connecting the PSU, I measured the following voltages to ground:
pin 1 (VIN) = 5.408 V
pin 2 (VSS) = 0.0000 V
pin 3 (VOUT) = 0.0002 V

Checking IC1201, pins 1, 2, 3 and 24 (anticlockwise from dot mark) are shorted to ground.

[lotas]

Thank you for your reply, I checked IC202 and indeed, its output is shorted to ground. Connecting the PSU, I measured the following voltages to ground:
pin 1 (VIN) = 5.408 V
pin 2 (VSS) = 0.0000 V
pin 3 (VOUT) = 0.0002 V

Checking IC1201, pins 1, 2, 3 and 24 (anticlockwise from dot mark) are shorted to ground.

Well, as I expected the answer that this would be the problem, all you have to do is replace the stabilizer, micom weltrend (program it in advance, it has internal firmware) or look for a new (donor) motherboard.