Simplest s-video mod ever for Vic-20CR

[Boray]

Now that I'm logged in, I can just as well re-post what I posted on Facebook some time ago:

Simplest s-video mod ever for Vic-20CR. You only have to cut a lead (elevated from the board).See attached pictures.

You need a connection cable, as seen here: ( https://www.kjell.com/se/produkter/el-v ... Wis4PaQNNg ) It's a cable often used with arduino boards and similar.

Cut the lead on the vic-20 board as seen on my picture and stuck the cable on there, and there is your chroma signal. What's left in your video port is your luminance signal. Make a special cable that you can plug that extra cable into. (I already had one of those, from a plug-n-play s-video-mod that required the vic-chip to be socketed. )

Do this on your own risk of course!

[beamrider]

nice, I keep meaning to get around to this. I bought one of the plug & play kits about 4 years ago and it's still in the box...

[joshuadenmark]

Thanks, great mod.

[English Invader]

Have you done much colour testing for games on your flatscreen? In particular, how do darker coloured sprites look with a black background? Are they clearly visable or are you struggling to see them?

[Boray]

Have you done much colour testing for games on your flatscreen? In particular, how do darker coloured sprites look with a black background? Are they clearly visable or are you struggling to see them?

Well, I haven't noticed anything strange. I have tried it on two different LCD TVs.

[siccoyote]

Will this fix the zig zag pattern on Red Cyan Magenta and Green?

[Mike]

Will this fix the zig zag pattern on Red Cyan Magenta and Green?

This is pretty much the point of all variants of the S-Video mod that float around there.

With the standard video circuitry, Chroma and Luma from the VIC chip are mixed into the Composite signal. Unfortunately, the Chroma signal strongly superimposes on the Luma signal, leading to those teared pixels you observe with Red, Cyan, Magenta, Green and also Orange. These patterns are steady on PAL machines, with NTSC VIC-20s they flicker at an 30 Hz rate and are not seen quite as easily.

The variants of the S-Video mod differ by the original video circuit to start with, and they also differ by the amount of "extra circuitry" put in place instead:

• The most widespread variant disconnects Chroma before it is mixed with Luma, adds a 75 Ohm resistor and 100 nF capacitor, and routes it to one re-purposed pin of the video socket.
• Slightly more elaborate: I replicated the amplifier stage of the Composite signal (now only Luma) for the Chroma signal. This adds some protection as the transistor buffers the Chroma signal (details see here).
• Now Boray's suggestion outlined in this thread here goes in very much the other direction. It "works", but does not provide any protection to the video chip (the first variant at least uses capacitive coupling to prevent the worst). If there is any significant voltage difference between Chroma output and recipient TV/monitor (for example, when the display is switched on/off), transients go directly into the VIC chip. In the worst case, this kills the VIC chip on an instant. Therefore this is a variant of the mod I definitely would not recommend.

Just my 2 ¢ worth,

Michael

[liveinabin]

So protection is needed to the video chip. I am learning a lot here.
As a new Vic 20 user (also, first post - Hi:) ) I’m a bit bamboozled by the sheer number of svideo mods. Any suggestion on what would be the best? I appreciate that different solutions would suit different models.
Mine, for instance is a PAL CR model (a 251040-01 Rev D) - the one with the diagonal resistor at R10 and a non socketed VIC.
I already have a C64 svideo cable (a ‘Retro Computer Shack’ cable with a 300ohm on the Chroma signal).
Ideally a mod that would let me use that - don’t mind soldering.

[Boray]

Because of Mike's comment, I made a small adjustment. See the attached pictures. This makes it electrically identical to the plug-n-play kit that was available some years ago. Thanks for the input.