24 Sep
1998
24 Sep
'98
8:43 p.m.
It's a CTX 1565GM, about 3-4 years old. Other than this focus drift
problem, it's a good monitor. I hate to trash it, but it's getting
pretty cheap to replace this size/quality. I'd really like to keep
it around to use as a VGA with older systems (>=10 years, of course,
so it semi-qualifies as "classic"!).
Tony Duell wrote:
How about slowly varying focus? I have a SuperVGA monitor that
won't keep its focus. If I focus it when I first turn it on, it
slowly goes out of focus as it warms up. If I try to keep it in
focus as it warms up, I can keep it in focus, but some of the other
adjustments peak out (like horizontal and vertical size). Is this
a power supply problem?
Interesting... It sounds like a high-voltage problem to me. I had a VGA
monitor where the focus and brightness went all over the place as it
warmed up. I traced it in the end to the flyback, which cost rather a lot
to replace :-(.
Anyway, in most monitors the focus supply (5kV or thereabouts) comes from
the flyback. As does the EHT to the CRT. And the EHT voltage does affect
the size of the picture (higher EHT -> `stiffer' beam -> smaller picture
for a given deflection field).
What I'd do is find the supply to the horizontal output stage. This is
probably around 150V. Having a service manual (what is the monitor, just
in case I have the schematics?) helps. If that drifts as the monitor
warms up, then debug the power supply. If it's steady, suspect a problem
with the divider network in the flyback.
-tony