S-video mod schematic for the schematic illiterate (For TG-16/Duo etc)

[ProfessorProfessorson]

AV Port is the same for all Duo models.

[DarkKobold]

Thought I'd post an update on doing S-video for a TG16 or PC engine that originally had the RF out. This is the easiest S-video mod to do. Some of you may already know this but I found better spots to tap moist signals needed. You can tap 5V and the Composite sync straight from two of the pins that originally went to the RF out. So if you de-solder your RF you can do your mod this way. So this saves having to run really long wires all the way to your expansion port and makes a sturdier connection for the transistor. Also, make sure to still use a 0.001 capacitor. There isn't one in the picture shown. I temporarily hooked it up that way for quick testing purposes.  

Thanks for this. Just finished up fixing a TG16 I got with a broken RF port, so this mod was perfect for that. This has now become my main TG16 for streaming video. The picture quality is mind-blowingly good. Thanks again, couldn't have done it so nicely without this image.

[blueraven]

I dig this, simple and effective. This is kickass, Prof.

[HercTNT]

want to do this myself, thanks mike for the circuit, thanks keith for the pic.

[Duo_R]

Nice to see you guys placing the svideo port in place of the rf port. Here is an idea for the audio - place a mini jack plug where the channel selector used to be.

[HercTNT]

duo, would love to see the internal on that one.

[Duo_R]

I should have taken pictures but was in a rush. Its pretty straightforward, gutted the RF box, then dremelled holes for the Composite video and audio jack. Then connected to the expansion port internally.

[jamisonia]

You guys are wiring the composite video straight into the Chroma pin?  That can't be right.  Wouldn't the damage already be done to that Chroma, since its mixed with Luma before you're tapping it?  Does that chip produce Chroma by itself? 

[ApolloBoy]

You guys are wiring the composite video straight into the Chroma pin?

It goes through a capacitor first so no, it's not straight into the S-video jack. I take it you've never seen S-video on the PCE/TG-16 in action?

[jamisonia]

You guys are wiring the composite video straight into the Chroma pin?

It goes through a capacitor first so no, it's not straight into the S-video jack. I take it you've never seen S-video on the PCE/TG-16 in action?

I have not yet.  I see it goes through a very small capacitor.  My concern would be since the chroma is already part of composite signal, and has been mixed with Luma, hasn't the damage already been done? 

[NightWolve]

You guys are wiring the composite video straight into the Chroma pin?  That can't be right.  Wouldn't the damage already be done to that Chroma, since its mixed with Luma before you're tapping it?  Does that chip produce Chroma by itself?  

Yeah, what Apollo said, the cap acts as a decent filter, but if you want the *best* result, you can disconnect the Luma in the amplifier circuit so that at the end of the Composite output, all you would have is Chroma and thus, no need for a filtering cap. That's how I wanna do my S-Video mod eventually and make a diagram for it as well.

You asked previously, how this S-Video craze got started. Best as I can trace it back to would be first here:

http://www.pcenginefx.com/forums/index.php?topic=9150.0

Bonkuts posting the circuit for the NEC Composite amplifier which showed that a working Luma was being outputted by the 6260 video chip and then thesteve posting his initial design for an amp here:

http://www.pcenginefx.com/forums/index.php?topic=10850.msg206287#msg206287

So I'd say early 2012 is when things kicked off with steve's initial circuit there. Then Keith Courage made the first clear, big image here revising it a bit after consulting with thesteve.

Drakon actually did it another way in the link below which was something I had been consulting thesteve about. I wanted to know if there was a superior way to produce/obtain a clean Chroma and if that was better than a filtering capacitor. He said yeah, it is. So here's that, (disconnecting Luma from the Composite amp to get a clean Chroma):

http://www.pcenginefx.com/forums/index.php?topic=12339.0

(I wouldn't recommend his technique for disconnecting Luma though. I wanna find an early trace and just razor it to achieve disconnection, rather than his idea of soldering off a resistor... This way, you could scrape both ends of the trace and solder them back to restore it if you wanted. Anyhow, you get the idea of what is trying to be accomplished here from that image.)

I wanna put all that together eventually but with a Luma + Chroma mix, since while this idea gives you the best possible S-Video, it breaks Composite output. So to do this right, you'd break the trace of the Composite output near the AV-Out and you'd add a basic Luma+Chroma Mix to restore back Composite support. So, you'd get the best possible S-Video output, while still having Composite support, only that it would be slightly inferior...



I think that is the circuit that those bi-directional S-Video-to-Composite adapters use. That's what you'd need to do if you did this the more involved way. It will be slightly inferior, yeah, but the benefit of the best S-Video output outweighs that con I feel. In principle, you'll stop using the Composite output anyway after such a mod. Thing is though, a lot of new TVs are phasing out S-Video support and you'll only find Composite, Component, or HDMI, etc. So, you don't want to be lazy and permanently break Composite support to get this quality gain, so it'd be smart to restore it this way should you go this extra route. There is a possibility that connecting that 470pF cap to your perfect Chroma and Luma lines to restore Composite ruins them when they travel out the S-Video jack... That was the other thing I was thinking of, so you'd want to put two new transistors so as not to attenuate your S-Video output in order to restore Composite and not have it interfere... (I dunno for sure if this will happen, haven't done it yet, but it's a concern). Not a problem at all if you don't care about restoring Composite though. You would simply have to make sure you get one of these:



So that if you switch to a TV without S-Video, you could still use Composite with it. Or, look into the Component mod we've been working on, once again, thanks to thesteve. I think Professor mentioned that these adapters can be better than the native Composite output if you've got S-Video to work with. I bought a cable that does this from RadioShack for a $1 (RS, can you believe it??), a close out item, but my experience is that it's probably that cheap circuit I linked above because the quality is inferior than the existing Composite output that I tested it against from my BluRay player. Anyhow, if you want the best, there ya go!

[thesteve]

that bI-directional mixer, is just that.
it would (contaminate your Luma, with chroma.

[NightWolve]

Ah, thanks for confirming it! So would my idea for a way out work ? Basically, having gone this extra route, you've got a clean Chroma line going to the S-Video jack and a properly prepared Luma line as well. You tap this clean Chroma and Luma, add transistors, attenuate them down properly with resistance and then connect that combining capacitor on the output end, thus restoring a Composite signal AFTER 2 extra transistors...

Would that prevent the contamination ? You combine them AFTER 2 transistors? If not, f*ck it, just sacrifice the Composite output for good and purchase one of these adapters or cables and keep it handy should you have to switch to a TV that only has Composite some time in the future.

[thesteve]

yes on the transistors, dont attenuate.
better idea is simply isolate the signals from the chip, mixing the luma/chroma after the first transistor
then have a transistor pair for S-Vid and the stock (almost) amp

[NightWolve]

Your circuit from the 3.5" LCD mod thread:



1) Break the Luma trace in the internal amp so at the Composite output, you have a clean Chroma.
2) Tap the Luma pin, build the well-known amp at the start of this thread, connect both clean Chroma and Luma to female S-Video jack.
3) Build your circuit pictured above (extra soldering to pins in question) to maintain Composite support, and who cares if it's slightly inferior since you'll mostly be using S-Video after this mod.
4) Break the Composite trace at some point near the AV out and connect it to this simpler amp, achieving a bypass, etc.

All in all, I would need 5 resistors and one transistor for this extra distance idea. (Of course, this was for TE and no lifting and grounding pins is necessary.)

Thumbs up or ? I think you cited a simpler idea but I can't visualize it from what I read.