Monitor repair

From: David C. Jenner <djenner_at_halcyon.com>
Date: Thu Sep 24 20:43:10 1998

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
Received on Thu Sep 24 1998 - 20:43:10 BST