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VIC 20 s-video mod problem

Posted: Tue Feb 12, 2013 10:55 am
by zybex17
Hi guys,
first of all, i want to say thanks to everyone on this forum : i love it!!!
Second, sorry for my english:i'm writing from Italy, and my english isn't too good, please be patient. ;)
Now, yesterday i tried the s-video mod described on this site, on my spare VIC motherboard. The problem is that i am unable to get colours out. If i touch the video pot, as told on the guide, i can get some very bad colours with noises, and if i go slighly further, the immage disappear. Turning it anticlockwise, i have a black and white immage. The strange thing is that sometime the immage quality is really good and crisp, sometime is noisy. I can't address the problem. I used a 1\4 watt resistor and a poliestere capacitor, marked as .1
I tried to arrange a cable without shield (with horrible moving screen), and with coax cable (with the results explained before). Do you have any advice for me? Oh, i forgot, i don't have a native s-video in on my LG tv (55lm660s), so i passed trough the scart port. Any help would be really appreciated (especially for the cable and\or the mod itself). I really would like to connect my vic with good quality immage. I still love to play and program with it. One last thing, for mistake i turned the second trimmer (the one for fine ttl adjustments), and i lost the original position. Is there a way to find the correct adjustment? It seems that it does nothing to the immage quality. I'll wait for your help. Thanks

Posted: Sun Mar 03, 2013 1:20 am
by a4000bear
It looks like you are only getting the Y (luminance) signal into your monitor. The weak and erratic colour indicates there is nothing coming in on your C (chroma) input, and it is picking up noise.

It's quite likely your scart cable is not wired to support S-video, or the monitor does not support it (I did a quick Google and could not find any real information on your monitor)

Have a look here for an example SCART pinout: http://www.diyha.co.uk/electronics/scart.html

Note that the luminance (Y) comes in on pin 20, and the chroma (C) comes in on pin 15, which is also the R input when using scart for RGB input. I suspect pin 8 is either pulled up or down to select RGB or S-video.

Of course there does seem to be many different variations of scart, so yours may not be the same.