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CRT Tube Fungus Removal

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The photos in this procedure have been graciously provided by forum member Boy Lex. Thanks Lex!

What is CRT tube fungus?

CRT tube fungus is a chemical reaction between the aluminum in the CRT housing and the glycol coolant instigated by the glow of the phosphor which in turn causes crystal deposits to form in the coolant chamber in front of the tube. It is not biological.

Fungus gets in the way of the projected image such that the image will look very fuzzy or out of focus in spots. It may start out with just some blotches but will eventually spread over the entire tube surface area.

It is a fairly rare phenomenon, but is easily (and cheaply) fixable with a bit of work and the right materials.

How do I know if I have fungus?

The easiest way is to remove the lenses and look in the tubes.

Below is a photo of fungus in a green air-coupled (AC) tube. Notice the splotchy spots behind the glass in the coolant chamber:

Here is fungus in the same green air-coupled tube seen above, projecting a dot pattern. Notice how the dots are not sharp at all, but out of focus:

Another picture of this green tube displaying a horizontal line. Notice that instead of being sharp, the line glows and diffuses the light such that everything looks out of focus:

Fungus in a green liquid-coupled tube. Notice the fuzzy text:

Note: Do not mistake bad focus for fungus. 99% of the time, bad focus is because of an incorrect setup. Take a look in the tubes (preferably with the lenses off) to make sure what you’re seeing is indeed fungus. For example, if you can’t get a sharp picture in the corners with your projector, don’t assume it’s fungus - it’s most likely an incorrect setup or limitation of your projector. It’s very common to not be able to achieve exactly the same level of sharpness at the edges of the image as in the center with many lower-end electrostatically (ES) focused CRT projectors.

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