A1502 820-3476-A no boot


I have an A1502 820-3476-A that doesn't boot.

I notice that just at power on (1~2 seconds) the fan starts to spin (I think that in those models that shouldn't happend), and progressebly increases the RPM, reaching full RPM after a few seconds. The CPU doesn't get hot, and that happend even with just the board connected on the bench.

When it reaches the login screen, sometimes it freazes after inserting the password, and other times it reboots after inserting password.

Already tried SMC reset and Pram reset but same result.

Even without the disk, the fan behavier is the same, but it stays in question mark for ever.

It looks like some bad sensor (not sure), but i can't see anything wrong on the board. The Apple diagnostics shows no erros.

Can you help?