Furuno crt screen burn

[Kajunbee]

We have a 4 kw open array furuno radar. After many years of s/b time the lettering is permanently burned into crt screen. Can someone give me insight into why this happens. I've never heard mention of it, but can it be reversed somehow.

 

[wwfeldman]

CRT screens are a phosphor material coating the inside of the screen
electrons fired from the cathode end of the tube impinge on the phosphor, causing it to glow

after a while, as you observed, some of the phosphor is burned off, and as in your case,
a "message" gets burned into the screen

the original personal computers used screen savers so that the electron beam did not
impinge on the same spot all the time, saving them from the problem you describe.

it wasn't too much of an issue with televisions, because they never had the same pattern all the time
it was a problem with any CRT - oscilloscopes and radar screen and the like, because they could be
showing the same thing for along time over years.

I do not think its repairable.
You might be able to replace the tube with another tube, (probably a salvage from a similar device) or with a modern flat screen.

 

[Kajunbee]

The screen is also getting more difficult to see in daytime. I guess this is also and associated problem with the phosphor screen. We have made a makeshift shield extension which makes the screen clearly visible. It reminds me of the older radars if your old enough to remember. They had a rubber boot that you put your face up to. After running around in the fog all day you would look like a raccoon. The aged rubber would leave black ring around your eyes. Any how I believe it's time to change it.

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One other question if you don't mind. You say that the phosphor burns away. Is what I'm seeing the etched glass formed by the electron beam.

 

[Kajunbee]

To clarify the question , the phosphor actually falls away and the exposed glass is damaged. As opposed to the phosphor remaining but being burnt and discolored.

 

[FvM]

The clarification is interesting but doesn't change anything to the general diagnosis. The tubes are done and need to be replaced. It's a regular lifetime problem.

Reduced brightness is most likely due to exhausted cathode.

 

[wwfeldman]

To clarify the question , the phosphor actually falls away and the exposed glass is damaged. As opposed to the phosphor remaining but being burnt and discolored.

Sorry.
I don't know.
I'll see if I can find out.