Reasons for S-Video mod (split/OT from: TQF: Physical release)

[Kweepa]

mini characters not so readable on my 12" green monitor, it's like every other line is slightly misaligned

The game uses cyan as foreground colour. While this choice of foreground colour aims to reproduce the retro experience on colour monitors, certain colours - namely green, red, cyan, purple, orange and their light variants - suffer from pixel tearing over black or white background. This is especially noticable on PAL VIC-20s with CR mainboard (like mine is). [...]

Presumably yellow would have the same problems on a monochrome monitor...?
That's what Yoho and Howay use.
Is there a way to preview this in VICE perhaps?
(Sorry about hijacking the thread. Perhaps a mod could split it out into a new conversation?)

(mod: done. original thread, see here. Instructions for S-Video mod, see here.)

[orion70]

I'll try your adventure collections on my green monitor tonight and take pictures.

[Mike]

Presumably yellow would have the same problems on a monochrome monitor...?

Yellow, blue and their respective light variants on white or black are mostly fine - there exist some barely noticable 'satellite' pixels to the side of each regular pixel, but in any case the even/odd pixel rows are not shifted against each other.

When the video circuitry of a VIC-20 shows those teared pixels, they also show on a colour monitor. The effect is not confined to monochrome displays. Also, on PAL, these patterns are stationary; on NTSC they exchange between even/odd pixel rows on every other frame, so the issue is not quite as apparent.

Is there a way to preview this in VICE perhaps?

Not yet. Currently the CRT emulation of VICE xvic behaves as if (any variant of) the S-Video mod was fitted.

[javierglez]

I'm pretty convinced this color arctifact only affects VIC 20 CR (the ones with the C64 PSU). I don't think the old VIC 20s show it. I'd advice to mod CR models but not the older ones. I was quite struck when I got 2 units of the older ones. I previously owned 2 CR units (plus my original one which broke).

[orion70]

I also had this feeling of better image with older models, but I guess the way they output video signal is pretty much the same...

Sorry for being late, I was stuck at work. I'll take pictures of YOHO and HOWAY on the green monitor ASAP.

[Mike]

[...] VIC 20 CR (the ones with the C64 PSU). [...]

Referring to a "C64 PSU" doesn't help too much to differentiate between the CR mainboard and the earlier types. It is the type of power connector that matters; it is either 2-prong with the first two main revisions of the VIC-20 mainboard (and slightly better video circuitry), or DIN with the CR mainboard.

To note: when the VIC-20 CR mainboard was introduced, the VIC-20 first got its own "wedge" type PSU which is considerably weaker in amperage than the corresponding C64 wedge PSU. Operating a VIC-20 with a C64 wedge is safe, using a C64 with a VIC-20 wedge overloads the PSU up to the point that the voltage regulator fuses - the resulting overvoltage then immediately kills the DRAMs in the C64.

More details to be found here: link.

[orion70]

Here we are... Sorry for the bad color of the picture, it's artificial light.

I'd say it's absolutely readable as it is by default, as I can't see blurry characters or other defects. Of course, being yellow and not white, letters are not "solid" as in the b/w version of The Queen's Footsteps. But the pixelated look is not bad at all, it adds to the retro feeling.

Also, I guess 30 columns instead of 40 make the reading easier anyway.

Overall, YOHO and HOWAY are already ok for the green monitor, but if we wanna try with white on black, well... .

[Mike]

[...] being yellow and not white, letters are not "solid" [...]

If you look closely, you see those satellite pixels that I mentioned before, to the left of each single regular pixel ...

Where there are two horizontally adjacent hires pixels, the satellite of the right pixel merges with the regular pixel to the left, which results in a somewhat brighter regular pixel.

Blue pixels on white background show a similar look (both are complementary colours to yellow and black).

[orion70]

Yep very clearly visible magnifying the image!

[javierglez]

...
To note: when the VIC-20 CR mainboard was introduced, the VIC-20 first got its own "wedge" type PSU which is considerably weaker in amperage than the corresponding C64 wedge PSU
...

In the 80s I had a VIC20 and a C128. My first C64, around 5 years ago, didn't come with a PSU. I believe it is OK to use a PSU if the stated watts and amperes match (and pinout of course). I think the link you provide the advise to *never* use a VIC20 PSU on a C64. But the pictures provided are good quality and the markings can be clearly read.

Had I decided to follow the advice I would have bought a "C64 PSU" probably identical to the "VIC20 PSU" I owned, and those are usually untested. Funny thing is later on I remembered I had a 1764 PSU I bought for the C128 (in a bundle that contained a mouse and GeoPublish too).

I think in the guide there's none weak "VIC20 PSU" with 5 pin connector for PAL VICs, it's NTSC-land only issue. I mean, the guide is good enough, there's no need to feed the idea that "VIC20CR PSU" and "C64 PSU" are different because in the PAL area I seriously doubt it.

[Mike]

I stand corrected: it was another VIC-20 PSU - not of the 'wedge' type, but the 251052-02 type - which had the DIN connector and which was dangerous to operate with the C64.

[javierglez]

It would be nice to know if older VIC-20s do have better composite image output than CR units. Even if the chips are identical, it could be some electric noise issue on the board, I don't know. Maybe it's been discussed before.

I was beginning to think this was common knowledge as I noticed CR Vics sell on eBay cheaper than early Vics, I don't mean low serial numbers or PET keyboards. It made more sense if reason was image quality not badge / PSU preferences.

BTW nice font, much better than 4 pixel fixed width .

[Kweepa]

BTW nice font, much better than 4 pixel fixed width .

Ah thanks, yeah, it's basically the VIC font with some columns sliced out.

[Mike]

BTW nice font, much better than 4 pixel fixed width.

There are only so many variations possible to design glyphs within a 4x8 grid, and I've seen much worse attempts at a 4x8 pixel font than mine:



It is especially unforgiving, when a font features lower case letters with uneven heights. This severely disturbs the read flow.

I *chose* the encoding to be ASCII, not PETSCII, for mainly two reasons: the main body of text out there is encoded in ASCII, so there's no extra conversion step necessary (which would anyway be incomplete, as both encodings miss out glyphs from the other one), furthermore didn't see any sense to include the 'graphic' characters of PETSCII as the font lives in a bitmap anyway, i.e. I can draw any graphic decoration besides text that I want.