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Dull color on my O2 with composite mod

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Hi everyone, 


So I had a composite mod installed and while it works, i noticed its colors are very dull..   This is the mod I installed.  I can say that i've had mixed results with the mods from this dealer (a good seller, not knocking them, as they don't make the mods) the intellivision mod was i'd say looks 80% right.. colors are not exactly true but not dull.. the Colecovision composite looks i'd say 95% and that's just being picky really.. it's pretty much perfect.. even still has that RF look on the text..  without the static / sync noise..  


Attached some pics to show what I see.. the last pic is from computer emulation so it's not a photograph, but just a quick comparison of the kind of blah color I show vs what really should be coming out more brilliant.. 


I understand there's a different mod out there sold by someone in turkey but the ebay listings won't work because of some paypal issues.  Maybe there's another way to order from this person?  I'd be willing to try a different mod in hopes of 


And yes I did turn the little pot to help improve the picture, but it didn't effect the color / brilliance much at all.  


Also the very last pic is the same O2 before the RF mod.  It had an issue and took a board from another O2 that didn't have that issue with the growing black bars.. so it's not like the game never could display colors well.  The person who did the mod removed the RF cable so I haven't gotten around to reinserting that and testing it, but yea this game has so few colors, I'd love to appreciate them.. 


I'm looking to make games for the O2 and I need to know I can trust the colors I see on the screen reflect what everyone else is seeing.  










Edited by Caleb Garner
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@Caleb Garner 


Your composite seems just incredibly dim. Like so dim that there must be an error someplace.

Either in the kit or the install but there is certainly something incredibly wrong.


I make a kit that puts out YPbPr. If your TV accepts it then it would look alot better than that.


There is a problem with a sawtooth pattern on the O2 but it can't be fixed without fixing the O2s internal clock (afaik).

So the clearer you make the picture the worse this problem gets. 

Edited by the_crayon_king
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yea the last picture with the black bars is no longer happening after replacing the board...   ultimately to fix that we replaced the board with another..  when i first bought it, those lines would appear to the right of various characters throughout different games. 


i had to hook up a sima copythis device for the extron switcher to see the image.. 


yea i'm all composite with my setup so I do need to figure out a solution that fits that.  There is one someone sells out of turkey, but they have something up with paypal so i can't buy the chip on ebay.  Chris Dota has been super helpful.  He installed the composite mod (he's done several O2 composite mod installations so he's not amature) but yea I do find myself questioning the chip itself.  

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@Caleb Garner I suggest the modder try a simple op amp based design. Like with the THS7314/THS7316. 

The modder would need a oscilloscope to find the max p-p; output from the op amp would be 2V P-P (unterminated).


You would use a resistor divider [on the input to the op amp] to lower the brightness until it is at that level (2V p-p)., maybe including a potentiometer to make it easier. 

The output should have a 75 ohm resistor and 220uf capacitor.


That combo of parts will work on literally almost anything that outputs RF; I find it usually looks better as well.


I could make a board for this if you think he could do some minor SMD work (soic-8). 



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Interesting suggestion.  The installation was done with a pre-made composite mod linked below. 




I'm not sure he's got the know how to do that and honestly he did me the operation as a favor for free.  


I have a local TV repair person that I believe could likely make sense of the suggestion.  


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Well this is the circuit I am talking about. The resistors on the left side are placeholders.


You only need to populate the parts you are using so only the stuff on the top left.

I am not actually sure what voltage the input is from the spot shown on the O2 board.

If it's not at least 1V p-p then something like this wouldn't work.


I would need more data to make more of the design. Specifically the p-p of the composite before it has gone into the mod kit.

Either way the IC and then the right end of the circuit is correct; the input resistors is probably the only thing needed.


If there is significant DC offset then the inputs would need a capacitor and a pullup resistor.

I guess I could add those as well since it won't hurt anything to add them when you don't need them. 

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That is the basic idea of the circuit.

This is a through hole thing (except for the THS7316). 

I only use SMD components so I don't know how much further I want to try to develop this thing.


I will put some thought into the needed components and finish the thing at some point. The layout wouldn't change but I'd have specific amounts for the resistors I stubbed in before. 


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5 hours ago, Caleb Garner said:

wow @the_crayon_king that's awesome.  Let me see what I can do to discuss this with Chris and see what he thinks.  Perhaps he knows something about this.  Either way I'm definitely determined to get this addressed.  Thank you so much for your insight and these suggestions!  

This may be an easier to understand circuit for Chris. 



That is actually a better circuit since I didn't consider before than the native composite is often lower than 1V p-p. 

This circuit now allows anything from 0.3V to 2V p-p. 

You would certainly need a oscope to set it properly but you could also eyeball it.


I may make that into a board sometime later. 

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This is the one for sale on ebay that's recommended from my friend but unfortunately you can't buy them on ebay due to some paypal problem in Turkey




very different looking than the one i have.  I'm sure these mod chips can be done many different ways.  Each probably has pros and cons.  My intellivision mod works well but colors are not exactly accurate but not terrible..   the colecovision mod is great overall except solid background colors tend to show some subtle vertical lines in the graphics..  

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