Jailbars in the newer Genesis/MD S-Video mod.

[SNKNostalgia]

Before I get to it: Over the years I have been using the traditional S-Video mod on my Genesis 1 model (Same as the Neo Geo mod back in the day).

After reading Xian Xi's newer mod on Jamma Nation, I just simply changed the simpler Chroma line-out. I read up on my Genesis on Sega-16 forums and found out it is the one with the "Stinker" audio quality.

My other Genesis 1 in the closet is the previous model with a real Yamaha sound chip... so I switch out the top shell and transferred the S-Video to it. This time I did the complete newer S-Video mod from scratch without all those resistors from the older system mod.

The video is more stable (no more white ghosts in black backgrounds with white text for example), the colors and picture is even more vibrant. The problem which seems to be hard to get rid of is the jailbars. Sometimes they are hard to see, sometimes they show up a lot (solid 1 color backgrounds).

Has anyone figured out a "Real" solution to this, other than making an external circuit or S-Video modding a 32X? If not... then I guess I am going down the RGB SCART to YUV convertor route.

 

[Xian Xi]

From what I've read the jailbars come from the chroma signal, just use a higher value resistor or pot to tune it then set it with the resistor value that's good if you want.

 

[SNKNostalgia]

I guess I will fool with it again. I tried a 68 ohm and a 73 ohm an got pretty much the same results. When I tried a 100 ohm, the picture was black and white. Might be the actual resistor I tried. Changing the resistance to get rid of jailbars will change the colors a bit though. I guess finding a sweet spot for my preference will do.

 

[Xian Xi]

Are you doing the cap and resistor on the chroma line or just a resistor?

 

[SNKNostalgia]

220uf elect cap and 73ohm resistor. Just like how your page has it. Honestly, I had some S-video jack problems towards the end of my adjustments till I tightened the inside prongs a little. I will fool with it in a bit.

 

[SNKNostalgia]

Still getting a black and white picture if using a resistor at 100+ ohms for chroma. I am using the logic chip in the front left of the console for my 5 volt to the transistor BTW.

 

[Xian Xi]

I'll check around.

 

[lastcallhall]

The jailbars on the CXA1145 come from pin 6, which is the x'tal in signal. It's taken from the board's 315-xxxx ASIC, and is required in any composite and/or s-video mod you attempt. I've even tried to lift the pin on the asic and wire an external oscillator directly to pin 6, but there's something in the way it's proceessed inside the CXA1145 that causes the jailbars. This has been a topic that's been researched extensively by myself and others on sega-16. The only way to eliminate the jailbars is to swap out the CXA1145 with a CXA1645 or CXA2075, both of which are NOT pin compatible (i.e., extra components are needed), and the 2075 is a surface mount chip, so you'd have to worry about this as well. The other option is to take the RGB & Sync signals from the chip and create a wholly new circuit. Personally, I've used these signals to create a component out circuit on the Genesis, but others have used the RGB & S signals and ran them into an encoder box, or they just used the scart cable.

So, in short, it can't be fixed 100% completely.