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Composite AV from TIA chip

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Does anyone have any guidance on how composite audio/video can be generated from the TIA's luma/sync pins? In other words, I'm not looking to modify the current video circuit to get composite, but rather build a new circuit for that purpose.

 

I've tried Ben Heck's rev 2 mod, but it does not seem to work as a stand alone circuit (assuming everything is connected right).

 

http://www.benheck.com/book/support/Atari2600VidMod.htm

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I've tried Ben Heck's rev 2 mod, but it does not seem to work as a stand alone circuit (assuming everything is connected right).

 

http://www.benheck.c...i2600VidMod.htm

 

I had the same problem with this mod when I initially tried it about a year ago. After watching a recent episode of the Ben Heck Show where Ben built a new Atari portable using this circuit, I revisited this mod. Same result as the first time... no dice. I watched the episode again and he glossed over the mod itself, however, there were various shots during the episode that clearly showed the mod installed on a 4 switch board. Using those scenes, the schematic, and a little trial and error I finally figured it out. I intend on writing a tutorial for the mod. If you can't wait that long PM me and perhaps I can walk you through it.

Edited by atariguy1021

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I used a simylar circuit. The picture was perfect, but only in black/white, no color... and for some strange reason, also no sound eventhough the sound is directly connected to the Atari chip. (I have the Darth Vader PAL 2600)

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I usually have to take color from a resistor elsewhere on the board, for what it's worth. The resistor changes depending on the machine you're modding.

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I will try that, thanks Jess...

The sound problem is fixed by the way, turns out that the capacitor I put between the output and the connector to the TV was broken.

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Still the same problem... Perfect picture, but only black/white.

I altered the circuit a bit and added the FMS6400 chip, like they use in the Longhorn mod. Now I do have color output, only there is a little bit of noise on the edges of the screen, but that doesn't bother me.

 

Thanks!

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I'm having a problem on a Atari 2600 black also, that I bought already modded.

 

http://youtu.be/dokSXUmgo8g

 

This game screen start moving during gameplay, while other games screen moves vertically from the starts, sometimes without sounds either. While other games works.

 

The guy who sold it to me says it could be a compatibility issue with my TV (Panasonic 50" plasma).

 

Any one would have an idea about this problem?

Edited by alexend

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old computer systems / games rarely put out a fully compatible video signal, and new tv's are kind of anal about what you feed them ... they may be more forgiving on the RF input cause its expecting crap to come in.

 

one way to tell is if you have a old tv, or just another tv is to try the offending games on it

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Also try different picture "modes."

I do not have plasma, but some 2600 games play better on my LCD TV in "Game" mode, while others don't play well at all, but are just fine in "Standard."

Other modes are called Movie, Vivid, Sports.

 

Something to try if you can't test on other TVs.

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Sorry, I was posting from my work and network policy there didn't let my start a thread, only reply to existing one. : ;-)

 

Since my post, I tried on another Pana 50" plasma, just an older model, and worked better with most games, but some would still rolls or even jitter.

 

I don't have any problem with my TV if I pass through a VCR. Using RF or Composite ouput of the VCR gives me bright and stable images. Though I still see hallows and "shadows" of objects on screen. Maybe this is normal though, I don't know.

 

That said, I was still not satisfied since I have to use a VCR... what is the point of paying for a modded Atari then? But after googling about mods and stuff, I saw that there is different approach out there and I saw another seller of modded Atari on ebay, describing that they use the "best".

 

After a few messages, he told me that they use the "batari mod" ant that he saw my post on atariage.... so this gave me confidence on his work and I decided to open my Atari that I just bought, to see what was done....

 

found out that the mode done by that seller seems pretty cheap Custom homemade board, not much on it except a few resistance...

 

I decided to buy another Atari from that other ebay seller with the batari mod. Hopefully this will give me better result.

Edited by alexend

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Greatings from Ukraine.

I try few mods, and finaly find solution. I do next mod on my Atari 2600 clone and it work. Point You must take colour (chroma) and not directly from Tia, I mark points red. Or, if You want, take it from Tia but You must repeat part of original sheme (mark blue).

post-40199-0-83101400-1409718765_thumb.png

post-40199-0-82174500-1409718806_thumb.jpg

post-40199-0-60944400-1409718813_thumb.jpg

 

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Hi !

 

Greetings from Slovenia

 

i know the story is about 2 month old , but i have a similar copy of atari 2600 hardware.

Could you please provide a few instructions for modding clone to s-video or composite.

like from which resistors (what are their resistance) have you tap which signal?

I can take a photo of my clone if you would be so nice to take a look and tell me where could i tap the signals.

 

thanks !

 

 

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In my post scheme, 4 points take directly from tia and 2 point you choose way to take from tia or from resistors which you can find trace from tia pins.

 

atari2600_tias.jpg?w=479

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On 9/3/2014 at 12:37 AM, parafin said:

Greatings from Ukraine.

I try few mods, and finaly find solution. I do next mod on my Atari 2600 clone and it work. Point You must take colour (chroma) and not directly from Tia, I mark points red. Or, if You want, take it from Tia but You must repeat part of original sheme (mark blue).

post-40199-0-83101400-1409718765_thumb.png

 

 

 

Hello from Canada, @parafin! Hope you are still around 🙂

 

I am building an Atari 2600 from "scratch" (as a learning project), and your circuit is a great fit for the video part - thank you for sharing! 🙇‍♂️

 

I started with the "top" part (everything above the 470pf capacitor), expecting a black-and-white image (with a minimalist test program expected to run on my partially built 2600) - which I got 🎉... but scrolling.

 

Did a lot of head-scratching, until I re-read your greetings... from Ukraine! That means PAL, right? Checking the menus, my TV indeed detected a PAL signal! (which explains the scrolling on my test program, it is doing a different frame size/rate!).

 

Given my carts are all NTSC, I wonder if you (or anyone) would know what to change on this circuit for it to work with NTSC.

 

Thank you!

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Posted (edited)

It's kinda obvious that my knowledge of PAL x NTSC is too tied to software 😅, but I am figuring it out. Hope these notes help more than hinder!

 

It seems that the part of the circuit I built is just the luminance signal, and that would not vary between systems. The color signal is what would differ (and hopefully, my TV will "understand" it's NTSC - like it does with my regular, modded 4-switch).

 

Also: for reference, the circuit above appears (with a lot of explanations) in https://www.atariage.com/2600/faq/index.html?SystemID=2600#composite (scroll to / search "chroma/luma output for 4 switch 2600") - minus the "Atari parts" (blue border) and the fact that it doesn't mix the chroma and luma (with the 470pf cap). Here is a screenshot for reference:

image.thumb.png.eed9d5fe70c2579b1a319d92e3b1e0b3.png

Edited by chesterbr
added screenshot for original circuit + clarified the chroma/luma junction

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And indeed, now the TV recognizes the signal as NTSC and the image on the TV doesn't scroll anymore. But it's still super unstable; which brings me back to traditional composite mod issues that I can debug 🎉

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