While projection screens themselves can become yellowed due to age or environmental factors like smoke, it may also be the projector itself that makes a screen look yellow. If you take the screen outside in the sunlight and it still looks yellow, you may be able to clean. If the screen is old and is still yellow after cleaning, consider replacing the screen. If the screen is white in the sunlight, examine the projector for the color problems.
The cable that connects the projector to the source of the video signal could be faulty. If using a VGA cable, it is possible that there is a bent pin on one of the connectors preventing a color from being displayed on the screen. An intermittent connection on a VGA or BNC twist-on type connector would cause the same problem. If the screen is yellowish, the cables or pins responsible for the color blue may be the problem.
An aging lamp can cause discoloration, including a yellowed image. Projector lamps are only rated for a certain number of hours. Most lamps should be replaced after about 2,000 hours of use. However, the life cycle of a projector lamp depends not just on how many hours it's been used, but how many times it has been turned on and off. The higher the number of hours on the lamp and the more times a lamp is turned on, the lower the lamp's intensity becomes. Most projectors have a built-in lamp hour counter, which tells you when it's time to change the lamp.
Dust, smoke and other pollutants that aren't noticeable on a daily basis do accumulate inside the projector, which is accelerated by its cooling fan. Dust buildup on the internal optics inside the projector can cause a yellow image. To check for this, adjust the projector's focus in or out until the debris on the internal optics comes into focus. Removing build up requires disassembly of the projector for cleaning.
Bad Optical Components
Within an LCD projector, there are polarizers that control the colors when they pass through the LCD panels. Over time, these panels can fail to pass colors properly and uniformly. Polarizers generally fail gradually and are identified by spots of discoloration, then eventual full-screen discoloration.
Projectors can have a longer life span when properly maintained and cared for. Most projectors have air filters inside the air intake vents. Frequent cleaning of these filters will allow for cooler operation, more effective filtering and cleaner internal optics over time. Leaving the projector running creates less wear on the lamp than turning it off and having to turn it on again immediately afterward. If the projector is not needed for more than four hours, it would then be beneficial to turn it off. LCD projectors as compared to DLP projectors will have a slightly green and yellowish tint to the image. DLP projectors replicate colors more accurately, with less yellowing of the image due to different internal processing of the video signal.
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