Non-destructive s-video cable

[Amon_RA]

Hi,

With the info on this board I decided to make a non-destructive s-video cable for my VIC20 :

Cap and resistor are hidden inside of the plug.
Grabber is used to connect to PIN2 of the VIC.

Very happy with the result, the image is so much better vs composite.

[Mike]

Hi!

It is not quite clear to me, how this is supposed to work. One important step in providing S-Video is to separate Chroma from Luma. Even if you provide Chroma on an extra wire by directly tapping it at the VIC - when you do not disconnect this output from the video circuitry, you still get a composite signal on pins 4 and 5 of the video out jack.

In another case, another Denial member also thought he'd get S-Video from an unmodded VIC-20 by just connecting it with an "S-Video cable" to the monitor. At that time, this was my reply:

http://sleepingelephant.com/ipw-web/bul ... &start=103

As I mentioned, I think maybe over at Lemon64, there was an S-video cable included with the Vic-1001 I bought from Dimitri a number of years back when he had his huge sale. There's a five pin DIN leading to an S-video plug and a mono audio cable, and I get a picture fine on my LCD TV using it.

So if the Vic doesn't naturally output S-video, I wonder what the cable is actually doing then...

Quite simple: unless the VIC has been modded, it outputs composite on two pins.

The TV then 'ignores' (most of) the luminance part of the composite signal on its chroma input, and (most of) the chrominance part of the composite signal on its luminance input, by filtering both inputs.

That 'works', somehow. There should still be some distortion of pixels, as some of the chrominance signal is going to be mistaken for luma, and vice versa.

[Amon_RA]

One important step in providing S-Video is to separate Chroma from Luma. Even if you provide Chroma on an extra wire by directly tapping it at the VIC - when you do not disconnect this output from the video circuitry, you still get a composite signal on pins 4 and 5 of the video out jack.
http://sleepingelephant.com/ipw-web/bul ... &start=103

I've placed a socket (with PIN2 removed) in-between the VIC and the board socket, that way the VIC chroma signal doesn't reach the board anymore and a pure chroma signal is taken from the VIC via the grabber. Luma is taken from PIN 5 - Audio from PIN 3 - ground from PIN 2 - of the video jack.
Chroma (cap + resistor) + Luma + ground are fed to the s-video plug, and audio and ground to the audio plug.

To undo the "mod" I remove the extra socket and use the old composite cable.
No need to cut traces or solder anything onto your vic-20.

[Mike]

I've placed a socket (with PIN2 removed) in-between the VIC and the board socket, [...]

Thank you. That was the detail you missed out in the OP. Of course, that detail given, your variant of the S-Video mod then works as supposed.

Note though, many later VIC-20s have their VIC soldered directly to the mainboard, so in this case changes to the mainboard are still necessary. You can understand the S-Video mod as 'repair' of an otherwise 'defective' circuit.

...

Oh, and welcome to Denial!

[orion70]

Excellent solution! Clean, simple, and non invasive. You (or someone else) should really sell it as a ready-to-go kit

[Mike]

Excellent solution! Clean, simple, and non invasive. You (or someone else) should really sell it as a ready-to-go kit

For what matters, mrr19121970 did this a few years ago already: S-Video conversion possible as plug-and-play solution?

[orion70]

Oh, I didn't notice that. Wonder if this can be brought again into the market.

[Amon_RA]

I thought about making a few to sell, but it takes way to much time for my old eyes and shaky hanks to solder those plugs.

[mathom]

Thank you for resurrecting this idea. I have almost everything I need to do this laying around already. I just checked my VIC and it is socketed. Looking forward to the improved video.

...mathom...

[Noizer]

I'm also thinking about probably messing up my oldie.
To start smelling something burned, I'm missing the value of the condensator and resistor that really counts. Perhaps schematix.