LG OLED65C7V-Z power issue

[Kievan]

Hello, I'm trying to repair an LG OLED65C7V-Z that has no picture and no sound. When I plug the TV, I hear the relay click. When I push the power button, i hear a second click and there are 3 red blinks but no sound and no picture.
I checked the voltage at the power board and I have the 20V and 12V at the mainboard connector, I have the 12V at the T-CON connector but not the 24V.
I tested the power supply without the T-CON and the main board by injecting 3.3V into the PWR_ON pin, the DPC pin and the 12VT_ON pin but still no 24V.
I checked the fuses, the diodes, the capacitors and I checked for shorts circuit on the power board and T-CON but nothing strange. The big transformer (in red) has 53V at his inputs but nothing at his outputs. The transistor (in blue) has 10 V between the middle pin and the others while the transistor right next to him has 110V, I checked the transistor in blue out of the circuit and he is fine. I checked the temperature with IR cam and nothing above 50°C.

I don't know if it is the T-CON board or the power board that has failed and if it is the big transformer (in red) that has failed.

Already thank you for your help and sorry for my English, I'm not speaking english regularly.

[Kievan]

I bought a new mainboard and now the TV functions properly. This is a mainboard for the 55 inch model but, for now, I have no problem. I'll maybe install a new firmware if a problem occurs.
Thanks for your help.

[MiltonSchuster]

Is your problem now fixed?

[Kievan]

Unfortunately not.

[lotas]

I tested the power supply without the T-CON and the main board by injecting 3.3V into the PWR_ON pin, the DPC pin and the 12VT_ON pin but still no 24V.

In order for the desired 24V to appear, on pin 23 (DRV_ON) of the power supply, a command to turn on must appear from the motherboard...

[Kievan]

Thank you, I applied 3.3V into pin 13; 23; 10; 24 and I got 22V and all the voltage were correct. So I guess it is not the power board, I'm going to investigate further on the main board tomorrow.

[Kievan]

I checked the main board and I found a resistance of 20 OHMs in the red area, it is not a short circuit but it is low so I checked the temperature and nothing overheat, the voltage at the capacitors are less than 1V. I tried powering the TV without some connections but that didn't change anything.
When I plug the TV in, there is one click and one second after (without pushing the power button), a second click and the voltages appear (except the 24V) and stay on until I push the power button or disconnect the tv.

[lotas]

Low resistance and low voltage (0.9 -1.0v) on the CPU core power rail is normal.

[Kievan]

I bought a new mainboard and now the TV functions properly. This is a mainboard for the 55 inch model but, for now, I have no problem. I'll maybe install a new firmware if a problem occurs.
Thanks for your help.