Saturday, August 2, 2008

Apple IIGS RGB video to Component converter

There is a fair amount of retro devices that output RGB.  But these were RGB in TV frequencies.  If you try to hook it up to most VGA monitors, they will not sync properly and you would probably get a picture with lots of lines (if you get a picture at all).  The monitors designed for these devices were readily available a few years back, but they are recently becoming more scarce.  Another way of using these signals is using a standard television with a SCART input and a RGB to SCART connector.  Most PAL TV's have SCART inputs (or so I heard).  Having gone through a local TV store recently,  I checked the TV's, both LCD's and CRT's ... somehow they stopped putting SCART connectors on the newer sets and it's been slowly replaced by component input (Y Pb Pr).  Also most NTSC TV's never had the SCART connector.

Well, that aside, another way to view the output of these devices would be to use the standard composite video out to your TV.  So I take my Apple IIGS, hook up the composite out directly to the TV's video in and ...

As you can see, the stuff that are supposed to be in black and white are tinted with color fringes.  This would be somewhat acceptable for games and applications with mostly graphics.  If you are using it with 80 column text, or graphical text, you will soon get a headache from trying to read it.  The Apple IIGS composite video circuits automatically disable the colour burst signal so you get something in black and white.  This improves the readability somewhat but on screens with combined graphics + text you get the same problem.  That is the main reason why the came out with RGB monitors.

Well, my TV has the standard Y Pb Pc component input.  If you connect something meant for RGB to it, it works, everything is as clear as RGB, but with the wrong colours.  That's a good enough start for me.  After searching around for a DIY RGB to component converter, I found one in my local electronics store already packaged as a kit.  It was published as a Silicon Chip article.  I proceeded and assembled the kit.  After that,  I think the TV expects the SYNC signal with the luminance (Y) signal, or it just displays the "no signal" blue background.  

A quick question to Tony Diaz (thanks Tony) gets me what I needed.  It is safe to just tie the composite SYNC signal with the Green output to have "Sync on green".  After wiring a makeshift  D15  IIGS RGB with wires leading directly to the RGB to component converter I finally have the results I was hoping for.  Here's are comparisons of using the composite "video in" image and the "RGB converted" image.  

Last 2 are output of the converter.
The image above is the same TV using the composite "video in".
This one is the same as above, but using the converter.  

Close up of the converted image.  Note the clear black and white text.

Last 3 various images of composite out.
Image of the same screen on converted output

Last 2 are pictures of the Tour of the Apple IIGS.  They are "graphical text".  You should be able to tell which is which ;)

That's the box itself.  Excuse the mess in the background.

Another 2 images for comparison... again you should be able to tell which is which.

More examples

Entire screens.


Unknown said...

Nice work. Is there a link to the kid that doesn't involve registering?

...jg said...

Would you consider making and selling these? If so, do you have a price in mind?

Jonnyboy said...

Rob, the link points to the website of the magazine that published the circuit I used. They do own the intellectual property on it and I guess they don't really want to give it away for free.

...jg the circuit has been made available by several local electronics shops and are being sold as a kit that you assemble yourself. The one I got cost Au$80 unassembled. I currently have no plans of making and selling these, though I may change my mind if there is enough interest. I'm sure it will cost a lot less for a bigger volume than the "price for one" above.

TimH said...

Holy awesome, Batman. $80AU is pretty inexpensive, too.

VectorJunkie said...
This comment has been removed by the author.
VectorJunkie said...

This isn't working out so well. First time using Blogger software. Here is a link to the schematic on their site. They have a free slideshow that includes this..


Drew ][ said...

Wow this is exactly what i have been waiting for lol. I have an RGB monitor but i know this 20 year monitor can't last for ever and getting fed up with Composite. Please make them and sell them :-)

Drew ][ said...


I don't fully understand what will or not work with various TV inputs. I am in the UK and have a TV with a Scart RGB socket and have purchased a cable that connects directly to this from my IIGS. Picture looks pretty damn good, but on a 32 inch TV is a bit big :-). Smaller LCDs dont have Scart sockets (specifically RGB ones) so i was looking at doing this to get component input which some LCD monitors now support. As I already have a scart cable from my IIGS could i just purchase a standard RGB Scart to component unit? rather than do the DIY method? or would i still end up with wrong colours?

Many Thanks

Jonnyboy said...

In theory converting the scart RGB to component should work. I have tried this on a large screen LCD tv and it comes out pretty clear. Problem is it blanks out every 5 to 10 seconds and then comes back. I'm not sure what's causing this and I will try to investigate if I find the time.

Drew ][ said...

Well i bought a Scart to Component Converter (CSY-2100) and though i get a picture the top of my screen just doesnt seem to stay sync'd. Possibly my TV..

vectorthom said...

Is there any reason why this wouldn't work on an NTSC tv?

Jonnyboy said...


If your TV is the HD type, it may be getting messed up by the IIGS' signal which is not quite 480i... is timing fools HDTV's into switching back and fourth between 480i and 720p. I don't know if there is a way to "fix" this but I haven't given up.


My TV is a NTSC tv. Well it's multisystem, but with component video this doesn't actually matter. If you switch the IIGS output to 60Hz it should appear like it does in my pictures (that is how I have it set).

Unknown said...

I sure would like to know where to find these at. I have a sony trinitron that has component in and would love to get this box (looked around on Google but didn't find one). right now i am running it into the TV using the RCA input

Unknown said...

Well, I have some good news. It will cost you roughly $38 + $55, but it appears, so far, to be will worth it.

Pick up one of these:



and you'll have exactly the same as above. I did have to open the Component converter and adjusted the color POTS inside to correct an overdriven blue signal, but it looks great on my Toshiba 20" CRT from 2003!!!!