Thanks for the offer, will keep it in mind. But to further develop my electronics knowledge I also am trying some stuff out. Caps are on both boards OK, I replaced the old ones for new ones. Solder joints are also OK. Diodes are OK, at least I get the expected readings on most of them. Although, there is one diode, x303, which has a reading that is much lower than the reading of the other diodes, but the reading for this diode is on both boards the same. And there are two diodes, x305 and x306, which show the same reading on the open side as on the closed side. One would say that these diodes fail, but on the other daughterboard the diodes act the same.
I am now doing some tests with transistors.