COLOR-MONITOR DRIVER BY MARTIN H. GOODMAN
At last you have at your disposal an extraordinarily simple circuit that does an excellent job of driving your color-composite monitor. This circuit represents a significant improvement over previously introduced versions for two reasons. First, it uses only the +5 volt line to power it, unlike several others that require +12 volts. This makes it considerably safer in the event of a short or goof in your construction, thus reducing the danger to the expensive chips on your board. Second, it is much simpler to build because it requires only four components. As an added advantage, it does not interfere with your existing RF output, as some of the earlier circuits do. You can also combine it with my monochrome monitor driver circuit (see page 36, HOT Coco, July 1983) and interface it to your CoCo in a plug-in fashion.
Complete Wiki page : Tandy TRS-80 Color Computer (CoCo) Composite Video Mod