Fw: Dodgy monitor

["Andrew Basterfield" <nospam [at] mailandnews.com>]

----- Original Message -----
From: Al Hudson <eah106 [at] york.ac.uk>
To: <sheflug [at] vuw.ac.nz>
Sent: Sunday, February 27, 2000 10:05 PM
Subject: Re: Laptop question


> Changing shape sounds very dodgy and probably more likely a problem with
> the monitor than the card. Your dot clock is either right or wrong,
> there's not really a gray area where the picture's okay one minute then
> screwed the next. It's unlikely that the Matrox is giving out duff video,
> because even if it was, the picture wouldn't change shape, it would roll
> and skew and stuff. If the picture's actually bending in or something like
> that, that sounds like a classic monitor failure, I'm afraid. At 2 months
> old, I would hope it's still under warranty ;) Try setting it up in
> Windows, that will show whether or not it's hardware or software (or at
> least, one would hope it would). Also, try it in a really basic 640x480
> mode and see if you can replicate the problem..

Forgive the technicalities... now we delve into the innards your monitor...

Changing picture width is due to poor EHT regulation in the monitor... try
it again with the brightness control set to 'detent' (centre position) and
contrast to max, these are the default factory settings for most monitors.
This is a noticeable characteristic of most cheaper CRT monitors, and more
likely to be a design flaw than an actual fault in your monitor. It is
caused by the fact that the EHT supply (approx 26kV) is more heavily loaded
when displaying a mainly white screen than a mainly black one (as it is
producing a lot more light), and as the EHT supply is derived from the
system that performs the horizontal scanning then a significant change in
the picture brightness level can cause a noticeable change in the width of
the picture. The monitors power supply _should_ be beefy enough to run the
tube flat out without noticeable change in width but with an economy monitor
this is often accepted as a reasonable trade-off for a slightly cheaper
power supply.


--
Andrew Basterfield
U/G Electronic & Communication Engineering (& ex TV/monitor engineer)
The University of Sheffield




---------------------------------------------------------------------
Sheffield Linux User's Group - http://www.sheflug.co.uk
To unsubscribe from this list send mail to
- <sheflug-request [at] vuw.ac.nz> - with the word 
 "unsubscribe" in the body of the message. 

  GNU the choice of a complete generation.