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I saw Commodore 64 to modern TV about how to connect the Commodore 64 to a modern TV. I don't understand all the details of the answer, so I wanted to try and ask something specific here.

In short, I just got a Commodore 64C and I have a VGA monitor. I have bought a converter box (specifically this one) that supposedly can convert S-Video to VGA. From looking around (for example here) it sounds like the S-Video out on the Commodore 64 isn't a "normal" S-Video output.

Is this correct?

To use a modern converter box, one would need a special cable (seen for example here) that maybe reduces the voltage or something.

Is this correct?

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The 64 has separate outputs on the video port for luma and chroma which you can adapt to an S-Video output. There are a few caveats, however.

The chroma signal is a bit "hot" compared to the S-Video standard. The S-Video spec for the chroma line for NTSC is 626.70mVP-P (75% Color Bars), 835.60mVP-P (100% Color Bars) and for PAL 663.80mVP-P (75% Color Bars), 885.10mVP-P (100% Color Bars). I've never seen anyone actually measure and post the output level on the 64's chroma line, but it outputs at a higher voltage than what the S-Video standard dictates. Presumably, this is because the 64's Y/C output predates the S-Video standard by several years.

This higher level output mostly results in over-saturated bleeding colours on a CRT TV but can result in all sorts of crazy colour-cycling nonsense on some LCD TVs, depending on how they process the S-video input internally. The "special cable" involves putting a 300-ish Ohm resistor on the chroma output to get the output voltage down closer to S-Video specifications. This gets you a cleaner S-Video output.

Really old model 64's have a five pin video port, not an 8 pin one, which doesn't actually have a separate chroma line in it. Instead it has just a luma and a composite output. You can technically use the composite in place of the chroma, but that's not really recommended since it won't give you a nice picture at all. The luma line can be used on its own for a good monochrome / B&W output, however.

One further thing you have to worry about though, as far as using an S-Video to VGA converter box. The C64 outputs a 240p signal, not a 480i (interlaced) signal. Not all converter boxes will support a 240p input correctly, it is hit or miss. Check the reviews carefully and see if people are complaining about it not getting a picture with their older video game consoles (NES, etc).

  • What are the symptoms of the out of spec signal? – traal Mar 11 '18 at 17:20
  • @traal The typical symptom is extra noise on the video output. The resistor is the easiest way to make the most improvement. There are more invasive mods you can do like replacing some parts in the RF modulator (the video signal passes through it), or to bypass the RF modulator completely and remove it (requires some additional circuitry), but most people find the resistor gets it "good enough". – mnem Mar 11 '18 at 23:45
  • Thank you for the answer. I hadn't come across the 240p vs 480i before. Would you be able to add a few more details to the signal being hot? – Thomas Mar 12 '18 at 15:52
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    @Thomas I expanded on that part as best I could. I don't have the equipment to test it myself and I can't find a post online with measurements anywhere. I'm pretty sure the 300-330 Ohm resistor value was arrived at mostly by trial and error by the community. Its also likely that the ideal value varies between PAL and NTSC units, as the spec is slightly different for S-Video for both. – mnem Mar 12 '18 at 21:46
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I'm not so sure about your question. The C64 signal is a pretty standard signal, but you got to use a Commodore specific cable anyway, as the C64 outlet isn't compatible to any standard. So buying a ready made cable will be the best solution - or wire one like described in the links you presented. Just take care that it's a 262° / DIN 41524 plug (not the more common 270° one often found on audio eq).

  • You can actually use the more common 8-pin 270° DIN plug, in a pinch. You just have to physically remove pins 7 and 8 since the layout is otherwise the same, and those two pins aren't used at all on the 64 (they aren't even connected internally). – mnem Mar 11 '18 at 15:20
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    @mnem It still needs some 'benevolen' force, doesn't it :) – Raffzahn Mar 11 '18 at 15:28
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    Indeed! Depending on the type of connector you have, removing the pins can range from "well that was easy" all the way to "well that's ruined now". Usually at worst a little heat from the iron and a pair of pliers is the most it takes though. – mnem Mar 11 '18 at 23:48

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