Hi all,
i have that notebook with fan always on, i have already disabled it on the bios and also reballed GPU but nothing.
Any help?

Thank you in advance.

Why did you reball the GPU ?
The fan is controlled by embedded controller (KB3926) which collects all temperature information of the system and then decides how fast the fan should work.

Reballed GPU because after some minutes turn off... restart only if GPU was cold. Also i have replaced KB3926 without success.

I think there should be a problem with a thermal sensor or one of thermal controllers.
The temperature information is collected by EC from these controllers.
You can locate which sensor is translating wrong or maybe not wrong data(if thermal diod inside a monitored chip is dead) by unsoldering the chip. I mean the data that cause the turning off.
Do you have enough time to look at temperature information of the sensors before the shutting down?

Some corrections:
You should unsolder the thermal monitor chip not main one.
Reballing a chip doesn`t make sense if a sensor inside is dead.
Checking the sensor information may give you some clue.