Finally, its a winner, thanks to you Martin.

I got the HK2500 tapedeck up and running.  Just new belts then OK.  Then I tried my testtape in it,  and the tape was full of dropouts, and very bad overall.
Then tested a lot of my old tapes and most of them had dropouts.
(Old tapes loose their megnetism)
But found 2 good ones (99 % good)   and gave them to B&O 8004.
Holy moses,  it worked.  !      Both channels, VU, dolby in/out,  timerdisplay.  All fine.

(until now, maybe some details isnt working, but so far so good)

So you were right Martin and I was getting "blind" and forgot the testtape,  and only focused on the 8004.
Thanks for keeping your interest and continued help.  Very grateful and happy.