Electronics > Repair
Repairing a video monitor in an IBM 3279 terminal
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bostonman:
I think most monitors have individual color (RBG) adjustments; usually on the neck board (which you need to be careful so you don't crack the CRT neck).

The CRT could be aged and the color guns are weak, which is a good possibility. I don't remember if the color circuits have capacitors that would go bad, but maybe those too are bad.

In any case, the color was adjusted by using a video source (or a piece of software) that displayed a white screen. Then, by eye, tweak the pots until the screen is white. Thought I still had software (which was on a 3.5") that displayed a grid pattern (for aligning new tubes), white screen, and individual colors, but I can't locate it.
inse:
Great to see it running again:-)
If the terminal has been used like this, mainly displaying green text, it’s not unlikely that the green cathode is spent.
The CRT rejuvenators try to remove a passivated emitter layer by overheating the cathode (afair).
The saying is that the fix is only temporarily, but are you planning to put 100‘s of operating hours on the set?
If you happen to know someone who knows someone that has access to a rejuvenator (and the right adaptor), give it a try…
m k:

--- Quote from: jmaynard on March 13, 2024, 12:48:04 pm ---I'm trying to bring an IBM 3279 color CRT terminal back to life. Following their diagnostic procedures, I've isolated the problem to the video monitor, a unit they purchased from an OEM.

--- End quote ---

Usually the monitor part is a some sort of a standard thing.
Maybe some old multisync monitor can be connected without a problem, if needed.
Some have sync polarity selectors.
Generally would be a mechanical mess though, sort of.
wasedadoc:
The "whiteness" should be adjusted when displaying both "just above black" and peak white. In the professional TV world one would use either a line sawtooth or a line staircase.  These let you see what is happening throughout the range as you adjust the controls.  "gain" or "drive" for peak white and "background" (or whatever name) for down near black.  Usually there is interaction between them so a bit of iteration is required.
bostonman:

--- Quote ---line sawtooth or a line staircase
--- End quote ---

Oh yes, I forgot about the staircase and/or gray scale going from white to dark (?) gray.
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