Hi Ryszard,
hard to say without seeing the circuit...

The connection from the PC to the hub will most likely be a "B" connector - looks like a little house when seen end on.



You will need to follow the GND printed circuit track to a point where it can be broken BEFORE it joins the feed to the outputs of the hub.

One thing to be sure of is you must break the track BEFORE the feed from the wall wart too.

That's about the best I can describe without the actual hub in my hands.

I do stress, try this with cheepie hub first, it is still my best guess, not a guaranteed fix.

--=-- My credo: If it's worth doing, it's worth overdoing - just ask my missus, she'll tell ya laugh --=--
You're only paranoid if you're wrong!