Date   : Thu, 13 Jan 2000 08:55:21 -0000
From   : John Simpson <Simpson.J@...>
Subject: Re: RGB -> Scart cable details

Now that Christmas etc is over I've finally finished soldering together my
RGB to SCART cable. Perhaps predictably, it doesn't work - but I've got a
fair idea why this might be the case. I wonder if anyone could confirm it?

Basically, I tested it my switching on my TV and plugging the (switched off)
BBC into it. I then flicked on the BBC and the TV immediately detected the
signal and switched to AV1 input. So far, so good. However, the screen was
completely black. It was also letterboxed, in other words there was a strip
at the top and bottom which was even blacker than the rest!

The only semblance of a picture was three horizontal lines at the top of the
picture: one red, one green and one blue. They were pretty feint. 

With a multimeter I tested the outputs at the SCART plug. The signal select
and sync select pins were +4.92v, Ov was, er... Ov, and the Sync pin was
3.92v. I put the high reading of the latter down to the high impedance of
the voltmeter compared to the TV, and reckon that the TV is actually seeing
about 0.8v, which is slightly too much. Of course, the sync signal must be
rapidly fluctating and so a multimeter probably doesn't give a very accurate
impression anyway.  

The Red, Green and Blue pins had 0.09v, 0.15v and 0.12v on them
respectively. I couldn't really understand why they were different to each
other. 

My current theory is that the voltage on the sync select pin is not high
enough, as suggested might be possible by Mike Cook. 

Has anyone got any alternative ideas?

john