Hello Remmel, sorry I have to answer in English:
In the old new forum there were many discussions on an issue with a faulty capacitor on the servo PCB. I had similar issue like you with a 6500 Beogram CD. I could figure out that it might be that because the CD player worked with CDs containing only few tracks, and when it was warm, also with CDs which failed when being cold (just plugged in).
It was then quite easy to order this cap, dismantle 6500, and solder the new cap into it. Worked perfectly again afterwards.
Maybe you can find a similar post in the Archived Forum.
In the next days I could search for type and brand and location of that capacitor
Regards, K