Date   : Mon, 25 May 2009 15:55:20 +0100
From   : francis@... (Francis Devereux)
Subject: S-Video mod for Master 128

On 25 May 2009, at 14:58, me@... wrote:

> On 25 May 2009, at 11:51, Francis Devereux wrote:
>
>> - With the S-Video mod in place, the composite video out looks noisy
>> (can anyone explain why?).
>
> I'd imagine because the s-video cable is acting as an antenna and
> injecting RF noise into the video.
>
> You should also be aware that this isn't "real" s-video - the quality
> of the image will be no better than a straight composite connection,
> TV post-processing notwithstanding.
>
> All you're doing is feeding the composite colour signal into both the
> lumen and chroma inputs of the s-video cable. This will indeed result
> in "correct" colour, but it won't do anything to get rid of dot crawl
> or any other kinds of composite video artefacts.

What I was hoping to do was feed the mono signal from the composite  
video socket into the luma input of the s-video cable, and the chroma  
signal from the emitter of Q12 (via the capacitor) into the chroma  
input of the s-video cable.  I'm not sure if the emitter of Q12  
actually has the chroma signal I want though...  I did notice some dot  
crawl so maybe not.

> The BBC lacks an s-video encoder so it's not possible to get "real" s-
> video out of it, unless you were to convert it from the RGB signals.
> (Which theoretically should work just fine, but such converters are
> not cheap. For example: http://www.js-technology.com/product_info.php?products_id=34
>  )
>
> The best picture quality on a TV from a beeb today is still an RGB-to-
> SCART cable.

Agreed.  Unfortunately my LCD monitor doesn't have an RGB input that  
will sync to TV frequencies, but it does have an s-video input.

Francis