Videomaster

[ComSoft6128]

I have a CampurSoft Videomaster (See CPCWiki page). The last time it was used, 20 years ago, it was working fine. As I don't have a technical background I was wondering if one of you hardware guys would like to have a look at it, the idea being to write a brief article about it and posting it on CPCWiki. It will be sent to you special delivery and I require it to be sent back the same - so unfortunately this means this would be limited to members in the UK. Over to you..................

[arnoldemu]

I have a CampurSoft Videomaster (See CPCWiki page). The last time it was used, 20 years ago, it was working fine. As I don't have a technical background I was wondering if one of you hardware guys would like to have a look at it, the idea being to write a brief article about it and posting it on CPCWiki. It will be sent to you special delivery and I require it to be sent back the same - so unfortunately this means this would be limited to members in the UK. Over to you..................

I would be happy to do that.

I would need it for a few weeks because I'd need to write some test programs to analyze the hardware, work out the ports it uses, their decoding, and find any interesting stuff about it.

Is that ok?

EDIT: Looking at it from the pictures there doesn't appear to be any software control on the CPC side..but it would be interesting to see what I can find out about it.

[Bryce]

The videomaster was a third party modulator, like an MP1/2 but without the UHF modulator. So it took the RGB/S and made a composite signal out of it. It was based on the Philips TEA2000 and although they went to the bother/expense of including a proper delay line, I would guess that the picture quality was pretty low. The TEA2000 could also only handle digital RGB as far as I can remember, so the picture would end up looking very Spectrum-like. This chip also happens to be the chip that the Spectrum 128 and plus machines used.

I'm not really sure what the idea was, because it goes to a SCART plug which, even back then, could take the RGB signals directly and give a better picture.

Bryce.

[ComSoft6128]

Arnoldemu, if you can send me your address I will post it off to you next week.
As regards the picture quality I can confirm it was excellent - you might want to look at the reviews in CPC Attack and Amstrad Action for a 2nd opinion on that.


Cheers,


Peter

[Bryce]

I saw the review and agree that as far as sharpness is concerned it would have been miles ahead of an MP1/2, but it still wouldn't be as good as a simple SCART cable would have produced.

Bryce.

[ComSoft6128]

Hi Bryce,


My understanding at the time was that RGB output was not acceptable to the CRT televisions available then and a conversion to composite was essential for the best possible picture. I am interested in your answer as I sold quite a few of these back then and if a scart cable had been an option I would have taken that route instead.


Peter

[Bryce]

The original SCART specifications (around 1975) included RGB inputs that would have been fine for a CPC from the very start. The only late introduction was S-Video which only got included about 10 years later. I would assume that most TVs with a SCART socket supported RGB input , as it would have cost almost nothing to include. I never tried RGB on a really old TV, the oldest CRT I had was from 1990 and had no problem displaying the CPC screen. However, the videomaster SCART cable seems to have been an optional extra, so maybe the device was originally intended for TVs that only had a composite video input and no SCART, which was also quite common back then.

Bryce.

[ComSoft6128]

Cheers for that

[ThomH]

The original SCART specifications (around 1975) included RGB inputs that would have been fine for a CPC from the very start. The only late introduction was S-Video which only got included about 10 years later. I would assume that most TVs with a SCART socket supported RGB input , as it would have cost almost nothing to include. I never tried RGB on a really old TV, the oldest CRT I had was from 1990 and had no problem displaying the CPC screen. However, the videomaster SCART cable seems to have been an optional extra, so maybe the device was originally intended for TVs that only had a composite video input and no SCART, which was also quite common back then.

Bryce.

Definitely in France the SCART/Peritel sets all accepted RGB input at least as far back as the early '80s — it's one of the reasons why the Oric was the best-selling micro of 1983 over there. It has no SECAM electronics at all, but offers RGB output so they just threw in a SCART cable. I think I read that it was a happy coincidence, the RGB output being there just because some connector pins were free.

[arnoldemu]

Definitely in France the SCART/Peritel sets all accepted RGB input at least as far back as the early '80s — it's one of the reasons why the Oric was the best-selling micro of 1983 over there. It has no SECAM electronics at all, but offers RGB output so they just threw in a SCART cable. I think I read that it was a happy coincidence, the RGB output being there just because some connector pins were free.

An update on the videomaster which I've been testing:

I used a composite cable with a sony trinitron CRT TV which has composite input. The image quality is slightly better than the composite->scart cable, it may be the same, but it seemed slightly better.

I opened it up and while it was on I carefully adjusted RV1 and VC1. The results were immediate.

RV1 appears to control brightness, at least that is what I saw on the screen. Not sure what signal it actually controls.

VC1 controls the colour. Too far left or right and the picture goes black and white on the trinitron, I didn't test that on the flatscreen. In the "middle" there is colour. Turning it left right makes the "colours move" (the rainbow effect I saw in mode 2 when using black for background and white for foreground) in different directions. I managed to find the sweet spot for my television and flatscreen which stopped it. Near to the sweet spot it kind of gently flickers, but at the sweet spot the colour is stable and I see white text when I should.

Now after that adjustment black and white in mode 2 is fine. Completely readable and useable.

In all modes, colours below 13 are too dark. I'm wondering if the Videomaster is using the luminance ("LUM"). I think it shouldn't. The luminance is only used by the green screen monitors. It's not used by the colour monitors and using it with colour, in my opinion, is wrong. The brightness on the monitor is not derived from luminance either.

Any ideas what L1 does? Is that adjustable?

[arnoldemu]

Colours are good, I wouldn't say spectrum like, because the reproduction of the pastel shades is good, and the picture quality is not as bad as some composite images I've seen.

[arnoldemu]

Apologies for the poor photos which are out of focus.

Normal CPC screen, mode 1. Sony CRT television. Composite cable.
http://www.cpctech.org.uk/SDC10827.JPG

mode 2
http://www.cpctech.org.uk/SDC10828.JPG

inks 0-15. mode 0 because it's easier to see.
http://www.cpctech.org.uk/SDC10830.JPG

inks 11-25. mode 0 because it's easier to see. (sorry doesn't show pen 26)
http://www.cpctech.org.uk/SDC10833.JPG

ink 13. mode 1. It seems a bit thinner.
http://www.cpctech.org.uk/SDC10836.JPG

ink 26. mode 1.
http://www.cpctech.org.uk/SDC10837.JPG

ink 26: white text on black. mode 2.
http://www.cpctech.org.uk/SDC10838.JPG

ink 13: grey text on black. mode 2.
http://www.cpctech.org.uk/SDC10839.JPG

mode 1. out &bc00,3:out &bd00,&82
http://www.cpctech.org.uk/SDC10845.JPG

[arnoldemu]

Previous were for Videomaster (composite), these are scart for comparison.

Same television, same camera, same poor focus, scart cable:

http://www.cpctech.org.uk/SDC10847.JPG

mode 2:
http://www.cpctech.org.uk/SDC10848.JPG

colour:
http://www.cpctech.org.uk/SDC10849.JPG
http://www.cpctech.org.uk/SDC10851.JPG

mode 2 grey:
http://www.cpctech.org.uk/SDC10852.JPG

mode 2 white:
http://www.cpctech.org.uk/SDC10853.JPG

OUT &BC00,3:OUT &BD00,&82
http://www.cpctech.org.uk/SDC10854.JPG

[Bryce]

L1 is the Chrominance delay, ie: the offset between chrominance and luminance. It's adjustable, but only with a plastic or ceramic screwdriver, because it's an inductor and putting anything meal near it will already effect its value.

Bryce.