Of course, very old thread;-)
The problem with the circuit is, that it is completely sealed within it's housing, so no easy access to the components. I will try to get it x-rayed by a friend this week, maybe everything clarifies after that.
I have a good command of electronics, so once the circuit reveals it's secrets chances are getting really good for a repair. I expect everything consisting of 80ies discrete electronics without too complex or purpose built components.
And also many thanks for pointing to the other forum with the gentleman from Canada. If nothing helps I will try to contact him. In the meantime I was pinpointed through a German forum to http://www.schiesssport.ch
where the owner(?) seems to be a former developer/technician with Hämmerli. For me, Switzerland is a little bit more closer than anything on the north american continent and might be the easier candidate for shipping.