Hi Mario,
I used to have a Minolta Dynax 500si and, as far as I can remember, it easily took a second for the screen to display anything. The autofocus motor is also very slow. So don’t worry that something’s rusted up. It’s best to ask Minolta-specific questions on the Minolta forum.
http://www.mi-fo.de/forum/
Enjoy your camera!
Best regards,
Guido