What's the model? If it is one of the DX5 or DX7 ValueJets, you may have a damaged transistor. Normally when a short occurs in those machines the entire head will stop printing because of a blown fuse. When only one color drops out I start looking at transistors as they control the head signal for each channel. However, before you start thinking electrical, troubleshoot the ink system including the dampers and maintenance station. It is far more common for this to be an ink flow issue rather than electrical.