Date   : Wed, 24 Oct 2007 14:14:46 +0100
From   : pete@... (Pete Turnbull)
Subject: OT was Re: UM1233 TV modulators...

On 24/10/2007 11:58, Anders Carlsson wrote:

> I thought the ZX Spectrum edge connector had a regular RGB signal, perhaps 
> at TTL level like the Beeb, but you mention it is a YUV signal? Never mind, 
> it is kind of off-topic for this list, although last time I opened my Model 
> B, I noticed the RF modulator looks the same way as in the Speccy. It 
> already has some "funny" connector with composite video, but I suppose it is 
> a B/W signal just like on the Electron and Master Compact? Doing the same RF 
> modulator modification, I expect I could get colour composite video.

It's a 75-ohm BNC connector, which is the industry (and official 
RS-170/SMPTE170M) standard for composite video.  Normally the signal is 
indeed monochrome, but later Beebs have a link (S39, not S38 as 
Wikipedia states) you can make to add the colour burst signal and make 
it colour.  On older Beebs (Issue 3 and earlier) you can achieve the 
same end by soldering a small capacitor (470pF) onto the circuit.  My 
manuals are at home so I can't tell you the exact location offhand, but 
I can look it up if anyone needs it.  That's an official Acorn mod, by 
the way.

-- 

Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York