<p>I carefully tried what "Dieter Schaefter" suggested - I used the mirror lockup, the mirror moved up without a problem and I tried the mechanical lever. The shutter did not fire - only a faint click sound. When I lowered the mirror, the mirror went to the same 1/4 position (only this time it is of course 3/4 of the way down, since the mirror was alle the way up) </p>