So I am not alone
Well, I think it is a problem of the connector. I tried to clean the pins, I took my multimeter and tried to find bad connections between the main board and the memory board but nothing. I knocked on every solder point, as long as I put some pressure at the top edge towards the analog board 4MB works.
I think the connector lost its strength and now makes bad connections.
Bye, a little helpless,
eweri