How to debug hot key disfuntion (on asus eepc) ?

Hello, I have an asus eepc 701, FreeBSD 7.0 RC1 + patch for the ath
wifi connection.
It work quite well, but I'm unable to use ALT+F5 which is supposed to
swicth between LCD and VGA port (with or without ACPI enabled).

Of course, it works on xandros which is pre-installed.

What can be done to track this problem ? Is it related to ACPI ? All the
laptops I had before (dell, hp) worked out of the box for this point.T

Thanks for any idea

-- 
HPC