S-Video Mod for PC Engine or CoreGrafx

[xelement5x]

So, with the whole palette issue with RGB I've been looking into doing a S-Video mod for my PCE. 

Voultar has a nifty little board here which I've downloaded and put together: https://oshpark.com/shared_projects/vmmVfv2H

My only issue is the instructions he provided seem to be specifically targeted towards the TG-16 hardware, not PCE.

From what I've read and researched the best signal to get are as follows:

LUMA: Follow pin 40 off the HuC6260, disconnect the 4.7k resistor it goes to (either remove totally or ground) and use that for luma into the chip
CHROMA: Follow pin 20 off the HuC6260 to where it connects with a 27k resistor, and connect a wire to the other side of the resistor for the chroma in

Are these correct or incorrect?

If correct, some help on finding these exact points on the PCE mainboard would be appreciated. 
I've attached a photo and outlined what I know exactly on it.



From my research and the above notes, it looks like I would want to:
LUMA: Remove (or ground) R134, attach the wire for LumaIn to the right pad where the resistor was
CHROMA: (This is where I'm unsure) Connect a wire to the right of R156 and use that as the ChromaIn?  I'm not sure between R141 and R156 where I should be grabbing the Chroma from. 

Any help is appreciated!

[Keith Courage]

I'm not sure from looking at the board where the trace goes either. If I was really persistent, I'd remove that first resistor R141 and see where the trace goes. You could also use a multimeter from the pin 20 via hole to test and see where it goes.


With the 4.7K removed for Luma, you can just grab chroma from the expansion port pin with no ill effects since the Luma is no longer connected to it. I'm sure there is another spot you could get the same signal from but it should be exactly the same with the 4.7k resistor removed.

[Keith Courage]

Actually, I just looked at that link you posted for Voultar's board. I wonder why there are spots for so many components on it. Looks like it isn't using the typically transistor amp method. So maybe you would need to grab the signal from pin 20 after all to use his board instead of the expansion port.

This is the method I use and the results are excellent. Only thing not mentioned on this pic is to make sure and remove the 4.7K resistor for luma(from pin 40) if you want a better quality video signal.

[xelement5x]

Thanks! I was debating if I should just pull off 141 and see where it goes to get a better idea too.
I spent some time yesterday cleaning off the flux between 141 and 156 on the left pads and it looks like there is a trace between them there after staring at it with goggles for awhile. I'll probably try there and see what I get, or just pull from the EXP bus like you mentioned.

I'm not why the board Voultar made is so complex either, I asked him about it on Twitter and all he said is he's not happy with it and wants to revisit it later.  I've been really happy with the other circuits he has made though so I figured I'd give this a try. 

I can always just use the method you've outlined above as well.  Seems like plenty of options to try and make this look great though!