All photos were overexposed. I suspected, that the exposure metering unit has been damaged. After disassembling the camera, I have found this:
(it was not separated in this manner, but it was no more on its normal position on the transparent base. The sensor is pressed down by a metal clip, but in the same time held in place with to drops of glue. The glue has been cracked.)
The lens has to project the image on the matte on the matrix made of the exposure measuring sensors. A small projector. This is the sensor matrix:
If it is not centered, the measuring will be of course false. The problem was, that the glue has been broken – so, how to get the right position?!?!?
Fortunately, on the surface of the transparent plastic remained a mark from the old glue.
Red arrow the mark, blue arrow the glue itself (you can put them together, they will fit).
I positioned the sensor in the right position under a microscope, and then I applied two drops of my favorite Loctite 3090 glue (2 component cyanacrilic adhesive – hardening in 5 minutes…)
And the camera works perfect!