Greenish or discolored patches that appear in the picture on your television screen are usually the result of magnetic fields that are disrupting the television's normal functioning. They are only visible when the television is on and are most obvious when the screen is all one color, such as blue or bright red. Fortunately, these blurry green spots do not permanently affect the television and can be corrected by locating and removing the source of the magnetic field.
First, look for the source of the problem. Large speakers, especially older ones, are the most common offenders. Notice the position of the green spot on the screen (left, right, upper, lower, etc.) for an indication of which direction the magnetic field is coming from.
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If you think you have determined the source of the magnetic field, try moving the object away from the television screen. If this does not work, continue looking for other potential causes.
If you are unable to determine what is causing the magnetic field, try moving the television. Sometimes magnetic interference can come from a neighbor's equipment, especially in apartments and condos. Moving the television to another part of the room, away from shared walls, may help.
If none of these techniques succeeds in removing or improving the appearance of the green spot, seek the assistance of a qualified television repair expert to determine whether there is a more serious problem.