@PsiDOC and Arcibald: Thanks for the hints. I'll check if I get them here in central Europe.
DOM is still working - I think/hope that this QF3 was the 'fuse' and all other components are OK. We will see.

@happyhammer: If you can see characters on teh serial connector (I advice to use putty), it is nothing defect - you will ahve problems with your connector usb2serial or baudrate.
My connection worked for about two month. I was on the way to make it permanent to make a hole in the cover of spare space of the second tuner. But I was not concentrated while connecting - bad, bad. No I can't connect - putty resting black - no characters nothing.