Reply to S4 Fader Malfunction

The far left fader suddenly stopped working. When a track is playing, I see the lights indicating level, but when I push the fader up no sound comes on at all, or it cuts in and out for fractions of a second. When I use the internal mixer, I can bring in the track just fine. However, as soon as I touch the fader again, it cuts to 0 and the volume goes off. I have calibrated the faders twice now, no luck.
Here's a video of the problem:
http://www.youtube.com/watch?v=TEgobP8S4c0