does this mean that both 24VAC and USB are plugged in at the same time when you did the firmware upgrade?
yes
has the controller ever worked with 24VAC
yes, before the update + now only with a USB connection.
perhaps the fuse is blown
I checked the fuse. It was ok
or other components were damaged
which ? I have no block diagram and no possibility to check it.
This is reason why I asked for any hints to check for the failures before I have to buy a new one.