Offizieller Kommentar
If you give the mixer a slight shake, do you hear anything loose inside? The tension system works on magnetic resistance; the more you dial it to "tight," the closer the magnet moves in the housing to provide that feeling of tension. While it's possible to open it up and service the fader yourself (you can even adjust the bumpers on either end for a different feel that way), if the magnet has come loose from either the fader or the adjustment plate, I'd recommend that you contact Pioneer DJ technical support in your region to have your hardware inspected and/or serviced.