monitor with screwed colour in bottom-right of screen

From: Tony Duell <>
Date: Fri Mar 12 18:07:15 2004

> posted to, but some of you guys might be able to
> help too...
> I've just been given a nice Iiyama 21" screen for free which seems to
> run quite happily, with the exception that the colours are screwed in
> the bottom-right inch or so of the display; the same sort of effect that
> would be achieved by holding a big magnet in that corner of the screen.

This is called a purity problem. There are basically 3 sets of
adjustments to a colour CRT/monitor over and above the ones for a
monochrome CRT :

Purity : Getting the red beam to only hit red phosphor, etc

Convergence : Getting the beams to hit dots next to each other

Grey Scale Tracking : Getting the relative intensities of the colours
correct (so that grey/white are neutral colours)

Gettign the purity correct depends on having a good shadowmask (or
equivalent in Trinitron, etc CRTs -- all these tubes work on essentially
the smae principles!). You then use magnets on the CRT neck to deflect
the beams slightly. Normally you set the thing up displaying a pure red
raster, at which point you hope the other colours are right too!

After setting the purity, you then have to do the convergence. This is
set (on modern CRTs) with more magnetic rings on the CRT neck, and also
by tilting the yoke slightly. I can remember, though, when there were a
dozen or more electrical convergence controls, and when you had to set up
the monitor in the position it was going to be used. Mind you, the
results were worth it (I've nver seen a modern TV that has as good a
convergence as my old Delta-gun Barco!).

> Degaussing seems to have variable effect; sometimes it almost cures it
> and sometimes it just makes it worse, but it never goes away.

You mentioned in another message that this monitor has suffered physcial
damage. And I may therefore have some bad news for you.

Try hitting (carefully!) that corner of the CRT with the palm of your
hand when the monitor is on. Do the colours change, and end up different?
If so, then I suspect damage to the shaddowmask or its fixing (I seem to
rememebr this is a Trinitron tube, the mask in those is a whole lot of
thin 'wires' running veritcally down the CRT).

Nothing much can be done about this short of a new CRT (even rugunning
places can't normally fix this).

Received on Fri Mar 12 2004 - 18:07:15 GMT

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