I have the same problem, but haven't fixed mine yet. I have, however, fixed the unit several times in the past. I can't explain how to do it, but it is pretty obvious and straight forward once you start taking the pieces apart. Just start by removing the plastic cover/housing of the star-shaped knob (knob first) and you will see what to do next.
2000 38' Dutch Star | 2006 Grand Cherokee | SilverLeaf VmsPc Engine Monitor | TST TPMS