raan@hp-pcd.UUCP (raan) (02/04/86)
The problem you describe is one of the bug-a-boos of color television. The screen of a color television consists of clusters of phosphors (red, blue, and green) which are each excited by a cooresponding electron beam to produce monochrome images with the needed intensities. The color image you see is made up of these monochrome images, with your eye integrating them into one image of the appropriate color. There are two adjustments that need to be made to make sure this all works as described: * Purity -- adjusting the raster scan so that the red electron beam only hits red phosphor and so on. * Convergence -- adjusting each beam so that it hits the correct phosphor dot to produce the desired mixing of colors. (IE a white dot and not a white dot with a red fringe on one side and a green fringe on the other.) Modern advances in TV design have made these adjustments much easier and have made them more reliable (IE don't get out of adjustment so easily). One of the factors affecting all this is the magnetic fields the TV is subjected to. The earth's field is a significant factor. In the old days, just moving a color TV around the room would produce results similar to yours. You see, the metallic parts of the picture tube, chassis, and supporting hardware can be magnitized. The resulting magnetic fields cause the electron beams to be diverted from their appointed paths and thus hit the wrong color phosphor on the screen. This produces a colored shading to everything on the screen. Depending on which parts were magnetized and how strongly, the affect can be blotchy and produce different colors. Newer TVs all have a degaussing circuit built-in to automatically demagnetize everything each time the TV is turned on. With what you did, it may have required several shots to clean it up. Worst case you would have had to get a service man to come out and do it manually. It is a good idea to keep magnets away from color TVs. B&W TVs don't have the same problems because they only have one electron beam and one color phosphor. --- Raan Young Unix mail: [hplabs|uoregon|orstcs|harpo|microsoft|tekronix]->!hp-pcd!raan