HP9836C colour alignment (grey scale tracking)
ard at p850ug1.demon.co.uk
Wed Sep 24 13:38:25 CDT 2008
I am working on an HP9836C, in particular the colour monitor part.
The original problem looked to be slight misconvergence, with red
fringes. But I think it wasn't really convergence problems at all. I've
been looking at the video amplifier PCB (the one at the back of the CRT)
which not suprisingly contaisn 3 identical video amplifiers along with a
blanking amplifier and components to pass the correct voltages to the CRT
Anyway, there's a resistor in each of the amplifiers that according to
the colour bands should be 12.4k. In the green channel it's close --
12.7k. In the blue channel it's nearer 17k, and in the red it's
open-circuit. And I think this could be messing up the HF response of the
red amplifer, hence the fringes.
The problem is that if I replace it, I'll have to set what HP call
'colour alignment' and what I grew up calling 'grey scale tracking'. I've
read the offical HP procedure (if you're interested it's pages 134-138 of
the pdf service manual on http://www.hpmuseum.net/), and there are at
least 2 problems
The first is that I don't have a suitable photometer. The second is that
even though it claims I need this photometer for the gain adjustment, the
cutoff adjustments are done to 'barely extiguish the raster' I've worked
on enough monitors to know that that's not precise at all, so I am
wonderign just how accurte the photometer _really_ needs to be.
Has anyone ever done this setup and can offer any tips?
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