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.