Thank you lxdude for confirming I don't make a handling the camera mistake. Yes, it shows in the finder A, B or the speed as selected on the dial.
I opened the bottom plate, there anything seems to work as it should. I won't take the risk to open the upper cap of the camera. (Last time I did let the camera with broken wires.) The screw holding it seems to be screwed in angled, so it is very much likely somebody worked in this camera.

Any idea what is hiding under the tiny cap upper right near the viewfinder?

What happens when using flash? I think it would not syncronise in the state it is now.