Fan output not working

[udicomag]

Hello,

I use a few dozned coral dev boards that work just fine. However, probably 2 out of 50 have the same
defect: the fan won't turn. For all my good boards the fans starts for a couple of seconds after powering up the board
and then stops. I can turn it on and off with shell commands.
For the defective boards none of that works. I swapped the fans between good and bad boards and the problem
always stays with the board, so the fans are good.
Is there anything on the OS/software side that may cause such problem ?
If I can't get the fan running I guess the board will overheat under heavy load.
Not a nice perspective.
Since I have more than 5 of theses defective boards (out of the box, no fan even before flashing the OS)
I wonder if that is simply a weak spot of the board design.
Any ideas ?

Thanks
Bernhard