Path: utzoo!utgpu!watserv1!watmath!att!dptg!lzsc!hcj
From: hcj@lzsc.ATT.COM (HC Johnson)
Newsgroups: comp.sys.atari.st
Subject: Re: All Black Screen Savers
Summary: All black could be bad
Message-ID: <1281@lzsc.ATT.COM>
Date: 9 Feb 90 17:16:04 GMT
References: <271*latornell@mech.ubc.ca>
Organization: AT&T BL Middletown/Lincroft NJ USA
Lines: 31

In article <271*latornell@mech.ubc.ca>, latornell@MECH.UBC.CA (Doug Latornell) writes:
> There have been some comments recently about potential damage resulting from
> the use of screen savers that change the screen to all black.  Could someone
> please explain this?  I thought the idea of a screen saver was to preserve

The problem is how all black is obtained.  The all black screen saver
selects 'external sync' for the video.
(An artifact of trying to work with a GENLOCK).  Since
there is no sync coming in on external, the screen goes blank.  The problem
is that the monitor expected sync pulses to keep its flyback oscillator
in time.

If a monitor tends to free run at a frequency too far removed from the missing
sync, the fly-back and the driver chips may overload and overheat.   Oscillators
are really strange things.

Also, with no sync, their is really no output signal (video information) either.
This can cause the bias on the video amplifiers to get to a point where, again,
they can overheat.

My old Mono, seems not to care about all of this.
My new Mono, hasn't complained (died) yet, but Atari did post a warning to
look out.
My old color, also seems not to care, but I don't run it often, or blank it
for long times.

Howard C. Johnson
ATT Bell Labs
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