There is no difference wheter the camera is loaded or not loaded with film. Still, when I push the trigger, the shutter activates and the mirror stays up. Moving the main switch to light position brings down the mirror and the shutter is cocked for next shot. So the fault is not connected with the film transport mechanism. It seems to be an issue with a faulty shutter. The camera would not see much use anyway by me, so a camera with new shutter would be overkill in my situation. Thanks for your input anyway.

Greetings Helmuth