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Thread: 32X S-Video Mod

  1. #1
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    Default 32X S-Video Mod

    Hey,

    I'm not sure if this is well known info, but I couldn't find any info on it, and found lots of contradicting and false info various places (and maybe my searching just sucks). I certainly don't claim to be a Genesis expert... I just figured I'd post some info and pics of what I did in case it helps anyone. This place seems to the be the place to discuss all things Genesis.

    Anyway, I finally picked up a Sega CD, and the proper cables for a 32X, so I decided to get it properly set up in my entertainment center. I was testing a few Genesis systems, trying to hear differences between different versions. But while doing that, I noticed on one of them that the video quality sucked (surprise... opened it and saw the KA2195D)... but when I connected it through the 32X, it looked much better. I also had a bad 32X cable, which caused lack of red. From these observations, I determined that the 32X must have a video encoder (not just overlay), bringing RGB from the Genesis (not composite).

    Then I got thinking about S-Video, so last night I probed around a little bit with the scope and saw seperate Y and C. Y is output on pin 22, C on pin 17, on IC12, though those are unfiltered, and look bad if used directly (ghosting, etc). They're actually filtered externally and fed back in on pins 21 and 19 (respectively), which is then mixed in the chip and output as a composite signal. Those are the pins you want to use (well, more convenient points on those nets).

    Like most of these ICs, you can't use the Y/C signals directly... you need to amplify them. I used the simple emitter follower amps... an NPN (2N3904) and resistor (+5V to both Collectors, Y to one Base, C to the other, and output resistors from the Emitters). I found a value of 100 ohms on the output made the S-Video look similar in brightness/color to the composite (though I didn't do extensive tweaking), and the signal levels looked good on the scope.

    To mount it, I took the two transistors, soldered the collectors together, clipped and bent the legs to the proper length/shape, then epoxied them to the top of IC12. Then I soldered them to the proper points (Y to the back lead of the unpopulated R46, C to the front lead of C77, +5V to the front lead of C80).

    Anyway, the picture looks great, and it's really easy to do. You can continue to use the existing composite off the A/V cable with this mod, and that cable is still used for audio. I haven't decided how I want to mount the connector (I'd really like to make a Neptune-like system if I get the time), so for now, the video is just connected with jumper wires.

    Attached are some pics of the install, and a couple screenshots. Unfortunately, it's really tough to get good pictures of the TV w/ my camera (bad moire). But you can see clarity vs. lack of clarity between the pictures, and I'm sure you all know the difference in quality between composite and S-Video. The TV also has a 3-line comb filter on the composite input, which already improves the image over a normal TV. I only posted one comparison pic, but of course it also works similarly for the Sega CD and 32X.

    I don't know how good this encoder is compared to an external one driven from RGB, but this one is already there and easy/cheap to use. It's clearly MUCH better than the KA2195D. If anyone does, or has done this mod as well as an external encoder, I'd be interested in seeing the difference.

    Here's the points to connect to:
    points.jpg

    Epoxy and heatshrink:
    installed.jpg

    Hooked up and running:
    connected.jpg

    Screenshot of composite through 32x:
    composite.jpg

    Screenshot of S-Video through 32x:
    svideo.jpg

    DogP

  2. #2
    I remain nonsequitur Shining Hero sheath's Avatar
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    Great first post. I am still hesitant to modify one of my 32Xs for this, but if the price is right and the directions are this explicit I may have to cave in!

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    Master of Shinobi omp's Avatar
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    Fantastic! Might give this a crack myself!

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    Master of Shinobi ooXxXoo's Avatar
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    I personally prefer op amps myself, but if the transistors work ok for you that's great ....
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    Quote Originally Posted by sheath View Post
    Great first post. I am still hesitant to modify one of my 32Xs for this, but if the price is right and the directions are this explicit I may have to cave in!
    Thanks... yeah, I've been a lurker for quite a while, but have been on a Sega kick lately... and I needed to post a question on the Sega CD anyway, so I figured I'd post this as well. It is really easy to do, and by just plugging the modded 32X in, you get beautiful S-Video for the Genesis, Sega CD, and 32X.

    Quote Originally Posted by ooXxXoo View Post
    I personally prefer op amps myself, but if the transistors work ok for you that's great ....
    Op amps are fine, but for unity gain video amplification, IMO you really can't beat the emitter follower. It has extremely wide bandwidth, very stable, and is a really small and simple circuit. Unless you're using an op amp specifically meant for video purposes, the bandwidth is usually relatively narrow (GBWP of several MHz is common), and because of the negative feedback on the op amp, you need to take special care to prevent stability issues. If you actually need to boost the signal levels, then I agree... a video op amp is great.

    DogP

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    Master of Shinobi ooXxXoo's Avatar
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    I remember trying the transistors about 2 years ago, but the results weren't all that great or to my liking...Only after teaking around with op amps all of that changed ....

    In your last pic with the 32X s-video screen shot for example, the image is quite dark compared to the composite video one, but maybe is just your camera ..
    Last edited by ooXxXoo; 04-26-2011 at 12:48 AM.
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    Quote Originally Posted by ooXxXoo View Post
    In your last pic with the 32X s-video screen shot for example, the image is quite dark compared to the composite video one, but maybe is just your camera ..
    Yeah, that's definitely the camera... you can see a couple darker horizontal bands in that one, as well as overall dimming of the TV and light in the reflection... indicating shorter exposure time. I actually had them both connected on different inputs, and I switched back and forth, trying various resistor values to get video that looked very close in brightness/saturation to the composite... as well as checking for proper levels (about 1Vpp on Y and 0.3Vpp on C). If you wanted to boost the brightness and/or saturation, you'd just bump down that resistor value a little bit.

    Unfortunately I don't have anything to capture the video directly available ATM, so the camera has to do. It really doesn't do the difference in picture quality justice, but like I said... everyone knows how much better S-Video is than composite.

    DogP

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    Master of Shinobi ooXxXoo's Avatar
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    Quote Originally Posted by DogP View Post

    Unfortunately I don't have anything to capture the video directly available ATM, so the camera has to do. It really doesn't do the difference in picture quality justice, but like I said... everyone knows how much better S-Video is than composite.

    DogP
    Of course, that's the idea

    ....
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    Wildside Expert tenchibr's Avatar
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    I did the Genesis Model 1 mod myself, took me a while... I would LOVE to do this mod, but I need a video guide to give me baby steps through it. Good job, and I hope someone feeling adventurous enough will make a video about it for me!

  10. #10
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    Wow! This is pretty awesome! It's a great way to get around crappy encoders or have S-video out in a modular manner, which is great for those of us who have a couple different consoles.

    Good work and welcome!

  11. #11
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    Quote Originally Posted by tenchibr View Post
    I did the Genesis Model 1 mod myself, took me a while... I would LOVE to do this mod, but I need a video guide to give me baby steps through it. Good job, and I hope someone feeling adventurous enough will make a video about it for me!
    Video guide? You mean like walking through the whole mod process in a video? I can't say I've ever seen that, or even really see the benefit. I get bored watching most youtube videos, and with pictures and text, you can go back and forth faster. If you've ever seen any of my youtube videos, you'd know how bad my camera work is... so I certainly wouldn't try to do any sort of walkthrough (and I don't have a tripod). The first picture really has all you need to do this mod.

    DogP

  12. #12
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    Quote Originally Posted by DogP View Post
    Video guide? You mean like walking through the whole mod process in a video? I can't say I've ever seen that, or even really see the benefit. I get bored watching most youtube videos, and with pictures and text, you can go back and forth faster. If you've ever seen any of my youtube videos, you'd know how bad my camera work is... so I certainly wouldn't try to do any sort of walkthrough (and I don't have a tripod). The first picture really has all you need to do this mod.

    DogP
    Aww, I wasn't necessarily counting on you to do it; the fact that you even proved it is possible is rewarding enough to me. But there's this one guy that had an awesome step by step video walkthrough, where I'd pause at the steps; without it, I wouldn't be able to pull it off. I am not as good with DIY mods as the community here.

    But here's the link to the video I followed: http://www.youtube.com/watch?v=1ikWV...el_video_title

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    Quote Originally Posted by tenchibr View Post
    Aww, I wasn't necessarily counting on you to do it; the fact that you even proved it is possible is rewarding enough to me. But there's this one guy that had an awesome step by step video walkthrough, where I'd pause at the steps; without it, I wouldn't be able to pull it off. I am not as good with DIY mods as the community here.

    But here's the link to the video I followed: http://www.youtube.com/watch?v=1ikWV...el_video_title
    Ah... yeah, I couldn't do that... I don't have a cool Aussie accent. Actually, the camera work on that is quite usable... you'd probably get sick watching a video of this from me. :P

    DogP

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    Master of Shinobi evilevoix's Avatar
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    Great post and I can see the difference. I just got me a SCART to Component converter, it looks amazing, no hacking of the system needed.

  15. #15
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    32x SVideo from it's chip is not new, but the tutorial is. Good job there

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