Denial

groepaz wrote:

I know for a fact this is completely false. C64 modulators are cheap and when they receive excessive levels of luma, sync or chroma they broadcast junk all over the spectrum.

and long before they will do that the picture will be complete shit - so why would anyone do it?

This may come as a surprise to you but what you just said is false too.

It is very very easy to change settings on the C64 modulator so it broadcasts garbage all over various TV channels yet you get a perfectly good picture both on the Y/C output from the 8 pin DIN connector and the RF output.

It is very very easy to change settings on the C64 modulator so it broadcasts garbage all over various TV channels yet you get a perfectly good picture both on the Y/C output from the 8 pin DIN connector and the RF output.

you must have a very different idea of what a perfectly good picture is than i do then

groepaz wrote:

It is very very easy to change settings on the C64 modulator so it broadcasts garbage all over various TV channels yet you get a perfectly good picture both on the Y/C output from the 8 pin DIN connector and the RF output.

you must have a very different idea of what a perfectly good picture is than i do then

You don't have a lot of imagination...

Imagine you have set the luma amplitude too high so the modulator does just a little bit of signal clipping when displaying white. If you connect a display device to the 8 pin DIN connector then you'll get a really nice picture, same if you connect to the RF output.

What you can't notice unless you have some top notch RF equipment or scope is this little clipping causes harmonics that you can't see on your TV and/or monitor. These harmonics get into the AM carrier signal mixer and end up completely out of the band of frequency the modulator's output is supposed to stay within. Also, you may end up with a modulation index of more than 100%.

See:
https://en.wikipedia.org/wiki/Amplitude ... tion_index

This causes harmonics to appear on RF unpredictably. So there you have it, just one of myriad ways you can have a perfectly good display while generating garbage at both the input and output of the modulator. This is also true on the VIC-20.

@Ken
I am a business partner with e5frog for PLAnkton solely. What he says concerning other projects does not concern me.

What concerns me is I know how to get a VIC-20 to output a good video signal and I know how to make a very simple S-video mod for a VIC-20, assuming it is adjusted properly in the first place.

cool, so in that unlikely event the RF reception noone cares about in 2016 is screwed up then?

what are you trying to say?

groepaz wrote:cool, so in that unlikely event the RF reception noone cares about in 2016 is screwed up then?

Hey... you're the one who wanted to argue about this ancient stuff...

You're quite right... nobody cares about RF interference in this range of frequencies nowadays, I guess.

what are you trying to say?

That you can't whine about a VIC-20 simple S-Video mod being problematic if you do it on a machine that has it's settings all wrong...

eslapion wrote:What concerns me is I know how to get a VIC-20 to output a good video signal and I know how to make a very simple S-video mod for a VIC-20, assuming it is adjusted properly in the first place.

A guide for getting a good output video signal and adjusting the Vic-20 properly would be welcome.

@Kakemoms
There are 3 different VIC-20 mainboards that I know of and each has a different type of video amplifier so 3 different guides would be required.

My own main VIC-20 is a "made in USA" type with Pet Style Keyboard. It is the one from which the s-Video mod photo was taken.

Generally, you want to adjust the output so it is as close as possible to this:
http://sleepingelephant.com/ipw-web/bul ... 9&start=64

Just note to a 6560/61 the blanking level and black level are the same. Trying to adjust to get 7.5 IRE for black would require changing things inside the chip and that's impossible.

The scope capture on the following post is for the Luma+sync signal on my main VIC so it's pretty easy to do.

I see I was quoted, don't know why and I'd like to point out that quotes aren't facts, not necessarily everything that I wrote either.

What's the problem? Seems there's some dick comparing contest here about who's right and who's not? I can't stress this enough, read it carefully: I'm not saying any of you are stupid... but if the non-stupid people try to explain to the stupid people why they're right - don't bother - as they are stupid they won't understand anyway - so stop trying to prove your point - let it go. How many pages of crap does one have to read through before getting somewhere?

If you're messing with signals going into the RF-modulator - of course it can have unwanted effects, question is if it's strong enough to affect anything - when the output isn't even hooked up to anything to the little metal box? Why would someone use a Lumafix64 and then hook up an RF cable? Even so, the lumafix is designed to lower the signal strength and/or insert an inverted signal of the same strength as the interference - lowering the total energy in the output signal, it doesn't amplify anything. Even if using RF you hook it to your TV and not to the central antenna, any interference will have to travel trough air - how efficient is that without an antenna?


This was a thread for VIC-20, right, so what's all the blabbing about C64 with it's built-in modulator?

Can't some nice moderator come in and clean all crap out, including this post, please.

This thread feels clean now!

Anyone wants real technical information to make a simple S-Video mod ?

As per Kakemoms request, I will try to setup a guide to adjust a VIC-20cr's video level with only a digital multimeter.

This specific VIC-20 is easier because it has fewer pots to adjust.

Kakemoms wrote:A guide for getting a good output video signal and adjusting the Vic-20 properly would be welcome.

Most digital multimeters are not sensitive to the higher frequencies of video signals but I suspect using a full black screen (POKE36879,8) with the upper half filled with solid white characters will result in a 60 Hz signal of the correct amplitude.

In theory you'd then adjust R10 until the output on pin 4 or pin 5 is at 0.714V with a digital multimeter set to AC.

This is for the VIC-20cr only, of course.

Can I resurrect this thread?

I just got a shiny new VIC-20 (NTSC CR model). The picture is not bad on a modern TV using composite, but the white level is a bit of a muddy gray. I would love to know how to adjust it without messing up the levels totally! I have a meter and a scope if that helps.

Bobbi wrote:Can I resurrect this thread?

I just got a shiny new VIC-20 (NTSC CR model). The picture is not bad on a modern TV using composite, but the white level is a bit of a muddy gray. I would love to know how to adjust it without messing up the levels totally! I have a meter and a scope if that helps.

If your scope can, like mine, trigger on a specific NTSC scanline then you're in luck.

Display a picture with black border and white background and adjust the signal to get something as close as possible to this:
http://sleepingelephant.com/ipw-web/bul ... 9&start=64

BTW, I note some nuisance has removed all the scope captures I had posted at the end of this thread...

I'll have to play with the triggering and see what I can do. It's not my scope so I don't know it too well ... it's an old 4 channel Tektronics, probably from the 80s.

eslapion wrote:BTW, I note some nuisance has removed all the scope captures I had posted at the end of this thread...

That could be me, I've deleted 49 posts on this thread