Re: Using IIgs with VGA monitor - how to go?

[salfter@salfter.dyndns.org (Scott Alfter)]

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In article <9G5ja.33187$7Im.15777@news04.bloor.is.net.cable.rogers.com>,
Glenn Jones <rg.jones@rogers.com> wrote:
>"Volkmar Friauf" <vf@apple2.com> wrote in message
>news:b6hisl$5a4p8$1@ID-60882.news.dfncis.de...
>> recently, picture quality of my IIgs Color monitor is degrading rapidly,
>> so I've been looking for an alternative. Since I have a fine VGA display
>> for my PC, I am looking for a way how to use that display with my IIgs
>> (possibly with a monitor switch so I easily switch between IIgs and PC).
>
>Slightly off topic ....
>
>I have a laptop that has s-video in and s-video out.. It also came with a
>s-video to composite conversion cable.
>
>I thought what the hay... so I conected up the cable...fired up MGI
>Videowave and there in the preview window on the LCD screen was the IIGS
>display.
>
>Monochrome looks great .... colour on the other hand was pretty bad... by
>toning down the brightness and colour level I could make the Desktop useable
>but with very little colour.

If there's a way to extract S-video from a IIGS, that might be doable.  I
don't have a schematic for it, but somewhere in the process of converting
analog RGB video to composite video, the Y and C signals that are mashed
together to form a composite signal must be present.

Start with the four signals on the RGB connector: red, green, blue, and
composite sync.  First, the video hardware converts RGB to YCbCr.  If you
mix Y with sync, you could take these three signals and get the same
component video that your DVD player produces.  Combine Cb and Cr and you
get C, which is one of the two signals in an S-video connection (the
previously-mentioned Y/sync combo is the other signal).  Combine the two
S-video signals together and you get composite video.

I don't have a IIGS schematic, but if these signals are available at some
point where they can be tapped off and run to a connector, you could get
S-video to your other computer's TV-in jack; this would be of much better
quality than composite video.  Another option (probably easier than hacking
at the motherboard) would be to build something that plugged into the RGB
output jack and provided component and S-video outputs.  If somebody makes a
13" TV with component and/or S-video input, this could be a suitable monitor
replacement.  (Component would be best, but S-video should be pretty
good...when I switched my TiVo from composite to S-video, I saw a big
improvement in the clarity of its menus.)

(FWIW, there's already a product on the market (the Video Turtle) that
converts RGB to S-video.  At $150 (according to the information I found),
it's still fairly spendy.)

  _/_   Scott Alfter
 / v \  salfter@salfter.dyndns.org
(IIGS(  http://alfter.us            Top-posting!
 \_^_/  pkill -9 /bin/laden         >What is the most annoying thing on Usenet?

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