Okay, seems like this case is resolved - I took my HFS-3 to home and then in a bright light saw the blown up MOSFET transistor.
I still can't believe this has happened... why? shortcut on the FAV wire?
below is the picture of schematic with a clearly seen melted plastic.
how can I check that it is really dead one?
http://aklepikov.ru/wp-content/uploa...0611-00016.jpg
can it be replaced by any other high-voltage/frequency MOSFET transistor?
seems like it is quite hard to get exactly this one in Russia - what are the key parameters to look for (I would buy new one tomorrow)?