Quadra - only red light goes on.

In addition to cleaning the plates on the cartridge, also turn the unit upside down then right side up a few times. There are 2 small wires inside the housing, and each has a ceramic ball on it that cleans the wire when the unit is inverted. Also, look through the vents to make sure the wires are not broken. If they are intact, they run in a straight line, almost the entire length of the unit.

If this does not help or the wire is broken, contact The Sharper Image. I believe this unit has a 5 year warranty. When mine failed, they exchanged it for free, even without a receipt.

Good luck!