kpackagekit does not show in systray

[Martin (KDE)]

Hallo

the last years I used to use yum-updatesd to automatically update my 
system. But as some users switched of the computer during update I 
thought of switching to packagekit (the KDE variant). On my newly 
setup laptop this works as expected. I got a Icon in the systemtray if 
there are updates detected.

On my other computer (the one previously updated with yum-updatesd) 
this does not work. I have set up the kpackagekit to check every hour 
but I got no icon in the systray. There are updates pending (yum in 
the command line told so). How do I get kpackagekit working?

Greetings

Martin