MOD GUIDE - Universal RGB-to-YPbPr/Component Circuit & Mod [8/24/2014]

[ConHuevos]

Anyone else get jailbars on a snes when using this?  Weird thing is, I don't get them with my TV but through my capture card.  I know its my circuit because I don't have jailbars when I run my snes via straight rgb to my PVM or my capture card (PEXHDCAP), I put 2 decoupling caps (2x .01uF) on the 5V coming to the circuit but doesn't seem to help any.

Anyone else have this?

[ConHuevos]

Got rid of the jailbars, added a 220uF and a 0.1uF bypass caps between 5v and GND on the circuit.

[turbokon]

Got rid of the jailbars, added a 220uF and a 0.1uF bypass caps between 5v and GND on the circuit.

I wonder if this will fix some of the jail bars I get on some tg16/pce with my component video boards. Do you have a pictures or diagram where you added the two caps?


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[ConHuevos]

For the TG16, I put 4 bypass caps on the encoder, and then 2 on the component circuit.

I don't use a 22uF like TheSteve suggested. 1 0.1uF Ceramic and 1 220uF Aluminum can in parallel for each pin.

I tried at first with just 0.1uF bypasses on the circuit and encoder but I still had bars.  I noticed on my oscilloscope I was getting some noise on the vcc line so I added the 220uF's in parallel with them, it got rid of them and reduced the noise greatly.


Then just put a 0.1uF and 220uF in parallel between your vcc and GND input on the circuit.

Screenshots using my PEXHDCAP to capture the Component:





It looks amazing on my CRT.

Big thanks to TheSteve for creating this circuit, it's great!

[MotherGunner]

Turbo, I can send mine back.  >=]

[turbokon]

Sure mother, you bet:)

Yeah, thesteve is awesome, without him, most of the mods wouldn't be possible.


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[turbokon]

I wonder if just adding the two caps to the component board will be sufficient enough to reduce the jail bars.  It will be benificial for component video installation in the ifu, dock or booster.


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[thesteve]

Look up coupling caps, or stiffening caps (same thing)
The shorter the wires the less its needed

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[turbokon]

I just added a 220uf cap to the component video board in a pc-engine with bad jail issues before, now I don't notices any jailbars.  I didn't have to add any other caps.


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[Helder]

Awesome thanks, currently making a board in Eagle to send to oshpark .

Oh nevermind...read your post in the sales section.

Turbokon really should edit his post as he is generalizing that all other console will only require 1k extra resistance on the RGB inputs, when it's impedance dependent.

Thesteve, correct me if I'm wrong, the 1kohm resistors are needed to help with the offset voltage cause by the genni's rgb lines outputting at a higher voltage then the pce. Impedance is something different, is the ratio of voltage to current in a ac circuit. This design operates in a dc, so impedance and resistance are the same. Theoretically, the additional 1kohm resistance should work with other rgb systems.

I'm curious about your design Turbokon, I notice thesteve's schematic on the front says 1K off the B, R lines, and 1K on the sync.  But on your PCB  you're using 2K on the R,B, 1K for G and 510 Ohm on the sync.

I can't tell from your genesis picture...but you added another resistor to the board, which is an additional 1K  on RGB?  So are you using 3K Ohm's off the R, B lines and 2K on G with the genesis?

Turbokon could you post the current Schematic since the first post doesn't have the correct caps or resistor values that you're obviously using in your design and what value trim pots are replacing what in the schematic.
I'm trying to get this to work on a Saturn and it does work but green is too strong and the colors are off a bit, I have a 100ohm trim pot in the Y output but that only brightens the image.

[NightWolve]

Turbokon could you post the current Schematic since the first post doesn't have the correct caps or resistor values that you're obviously using in your design and what value trim pots are replacing what in the schematic. I'm trying to get this to work on a Saturn and it does work but green is too strong and the colors are off a bit, I have a 100ohm trim pot in the Y output but that only brightens the image.

Steve says the OP schematic is correct, except all cap values are 22 uF ceramic and that's good enough (That'll let you make a smaller board, no big 220/470 uF caps). Anyway, you're trying to use this design for a Saturn and so the source RGB signal is not gonna be quite the same. Like the Genesis, it's going to require some fiddling. I dunno about ole turbokon revealing any changes he made as he's selling a factory-made PCB of it. But from what I can tell via the photo of his PCB, he used 10k pots for R4 and R6, those 6.5k resistors, making that aspect adjustable. So there's that, and I'd say you'd want to add extra resistance to your Green line as well given your particular case.

[Duo_R]

for universal setup perhaps some pots could be implemented? I know each of my systems RGB always needed a little adjustment to look right. As Wolf stated they are all a little different.

[Helder]

I had some oddball things happen and I had sync but colors were whack then after adding pots the image got a little better but my connections weren't great so I couldn't make proper adjustments.
My blue wouldn't do much when I tweaked it and then I noticed I had a 5v wire come loose that goes to the 22uf cap on the blue line and once I put that back the colors came out strong again instead of dull and almost black and white.
The only issue I have now is the SYNC which is making the screen jump, I had been using the Composite video and sync and was working fine but now it doesn't and the Saturn does have a Sync pin which I also used but its still not keeping the image stable.
So does anyone have any idea what to do to the Sync part of the circuit to stabilize the image without using a LM1881 which I do have but would like to avoid it since it was working fine not too long ago. I didn't touch anything on the Sync part of the circuit.

[turbokon]

Here is the layout for my boards.




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[turbokon]

This boards works with the SNES/genesis by adding 1kohm resistors to the rgb signals. May just need to play around with the rgb resistors value for the Saturn. I will test with pots to see if they will work universally.


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