External RGB to S-video schematic

[MEGADRIVE Jeroi]

This schematic is still on DEVELOPMENT state.
if you have ideas or suggestions, please join and discuss them.


This is internal or external circuit and a layout made by me:

This is replacement circuit for sony cxa chips in genesis NTSC console and variety of another RGB consoles. If you want to add for some reason s-video to pal you need to ground pin 1.

Composite sync (CVBS) or Csync input:



Note: This is layout is for older equipment which might not output from VDP H- and Vsync, there for providing sync with Compositesvideosync (CVBS) or Csync alone.

Hsync & Vsync input:



Note: CLK pin is NTSC (or pal) clock signal which is going to sony chip also. Take it from there.

More info can be found here: http://www.cpcwiki.eu/index.php/RGB_SVideo

Component list:
- AD724 (only available as 16pin soic afaik but practice makes pros and lot's of youtube videos about surface soldering)
- 5*100nF ceramic
- 1*100uF elko 6mm dia
- 4*220uF elko 8mm dia (important bigger dia elko dont fit to mobo design)
- 1*4.7pF ceramic or similar value depeanding on the output if it is good enough. If not change this one to another value.
- 6* 75ohm 1/8 resistors (important board not desinged for 1/4watt resistors but if you put resistors standing they will fit.)
- 1*1N4001 diode

Layout image:



Note: The composite layout is same layout but no vertical sync input.

Board size: 45mm*33mm

Version:
1.0 - I changed orginal layout resistor from green to blue as I think it was layout fault in orginal author layout. Please report if the mobo don't work.

For AD724 testing:

Here is layout image for testing AD724 on Solderless board. So you can build the circuit adding Metal pins to Dummy DIP16 pins or use cables and solder them to dummy pins, then attach to solderless board.



PDF added to attachment.

[Drakon]

Building a circuit to divide the oscillator frequency down is doable. Thanks to tiidos help I built a circuit that takes the 21.4 mhz oscillator in the nes and divided it down to 3.58 mhz to drive my encoder. But I guess if you're looking to save on needed parts...

[MEGADRIVE Jeroi]

Info moved to top post.

[MEGADRIVE Jeroi]

I am nearly done the circuit for internal cxa relpacement board to get s-video and combosite with newer generation ad724 encoder chip. Stay tuned.

[MEGADRIVE Jeroi]

First version ready, used the site's circuit but I guessed that it has fault on one 75ohm resistor because it was going to green and blue was without resistor at all. So I wired the resistor to blue instead. If this dont work please report.

[retrogamer343]

Hello and thank you so much for this info. I have been trying to find a good way to get s-video out of all my consoles. I do have a couple of questions:
Is your schematic a replacement to what is currently in the genesis or in addition to? In your schematic what is CVBS on pin 16? Thanks.

[MEGADRIVE Jeroi]

Well CXA's are a bit poor s-video producer and they produce rainbow banding and horizontal jailbars and such. This circuit is intended to replace CXA completelly and encode composite plus S-video with newer encoder chip.

Composite input. Excatly what you get out of composite pin on CXA* chip output or you put Csync going into CXA directly. Hec I will make Hsync and Vsync version also. We will not use CXA at all by adding both Horisontal and Vertical sync from mobo directly but I was concerned because all the consoles out there outputs composite but may not output H/V sync.

[omp]

Matey to make things easier, you could make a imgur account or similar. That way the pics are full size and not thumb nails. It is free to set up and pretty easy (if a dumb ass like myself....)

[MEGADRIVE Jeroi]

Matey to make things easier, you could make a imgur account or similar. That way the pics are full size and not thumb nails. It is free to set up and pretty easy (if a dumb ass like myself....)

Done.

[Drakon]

again everyone is so sure that any issue is caused by a cxa video encoder....ooookay.

[MEGADRIVE Jeroi]

I am redoing the layout as I removed caps and resitors from rgb input. You can take direct rgb from cxa input legs. Also removed diode as it only is there if power is connected wrongly the AD724 would fry. So incoming next layout version. While removing resisitors and caps, when this circuit is build, you can take a look if color artifacts are present. If yes, then the cxa input pins has some sirious proplems in generating jailbars and color bleeding.

[Drakon]

Just so you know neobitz had a ad724 based s-video encoder circuit for sale years ago (so long ago I don't think it's even around anymore). Plenty of people complained that it doesn't work with the sega gensis. In fact I bought and built one and it doesn't work with a sega genesis. But what do I know....apparently I'm just an "arrogant prick". Maybe it's a better idea to actually TEST something instead of just posting schematics all day and expecting other people to do the work for you.

[omp]

Done.

Ah my lad-oh much better! Looks good!

[MEGADRIVE Jeroi]

Ah my lad-oh much better! Looks good!

Thank you

[MEGADRIVE Jeroi]

Just so you know neobitz had a ad724 based s-video encoder circuit for sale years ago (so long ago I don't think it's even around anymore). Plenty of people complained that it doesn't work with the sega gensis. In fact I bought and built one and it doesn't work with a sega genesis.

Thats why this thread is arround. Let's make it to better, Lets make it work. I love you uuuuh tada dim tada dam.

You know what Drakon, This is fairly new way to develop circuits, but it was first course in University on Applied Scienses, newly started course in few years ago in Germany, Problem Based Learning, where you divide poeple into groups and you need to come togehter with idea, development and problem solving into working product. How I am applying this solution to generate first layout version, to inspire more people to join into help and make problem based learning out of it. I see you are suggesting that past sircuit with AD724 did not work with Genesis, I have heard you, and I will take a look in that matter in coming weeks, but my encoder is pal mode but what changes is pal sync signal and first pin gnd and such things. But if there is problem I will surely take a look of those signals and see what is caussing the problem. Thank you for your information.