38 replies to this topic

[Ransom]

Glad to hear the V2 project is moving along! Thanks also for the clarifications on the 4-port/2-port issues and CRT/LCD issues.

I'm really, really looking forward to being able to buy one of these bad boys.

[GeneralMurdock]

and I got my atari 5200 today!! The RF is not bad but it's not hardcore great quality as S-VIDEO. I never saw RGB/SCART in my entire life so for my humble soul s-video is "da shittz!" LOL

[Rex Dart]

GeneralMurdock, on Fri Feb 17, 2012 11:26 AM, said:

and I got my atari 5200 today!! The RF is not bad but it's not hardcore great quality as S-VIDEO. I never saw RGB/SCART in my entire life so for my humble soul s-video is "da shittz!" LOL

Don't worry; all component signals (S-Video, RGB, YPbPr) look pretty much equal at standard definition & lower.

[Gandor]

low_budget, on Wed Feb 15, 2012 11:43 AM, said:

I do not currently have my installation instructions online, I just include a paper copy with the boards. I have revised them so they cover early 4 port systems though. There are only a couple differences.

Could you make a pdf and attach it to this thread?
Or I can pm you and give you my email and send it directly to me?

Thanks

[walter_J64bit]

Does this s-video mod work with the VCS adapter?

[Prodos8]

walter_J64bit, on Tue Feb 21, 2012 5:46 AM, said:

Does this s-video mod work with the VCS adapter?

Nein.

No mod that takes signals from the GTIA will work with the 2600 adapter.

[walter_J64bit]

Prodos8, on Wed Feb 22, 2012 11:07 AM, said:

walter_J64bit, on Tue Feb 21, 2012 5:46 AM, said:

Does this s-video mod work with the VCS adapter?

Nein.

No mod that takes signals from the GTIA will work with the 2600 adapter.

LOL, I hope there's going to be mod that's compatible with the VCS adapter, I'll just keep using the FR out.

[low_budget]

I got the v2.0 mod installed in a 4 port system I recently acquired. I can already see an improvement over the v1.2 board. Installation was a little more tricky (and permanent) as 6 GTIA pins had to be bent straight.
I tried two different configurations so far, the first was as designed and based on the Atari 800's circuit. This one had excellent contrast, but some color bleed.
In the second configuration I bypassed a transistor in the chroma circuit and connected pin 2 of the FMS6400 to ground. This made the color bleed almost unnoticeable. I'm happy enough with this version to offer for sale in limited quantities.
I don't have an Atari 8 bit computer, so I wasn't able to test on one. If somebody would be willing to give it a try and post some pictures, I would be willing to send them a free (bare) 2.0 circuit board.

I will post the v2.0 schematic eventually. I still have some changes I would like to try first.

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[low_budget]

I finally got a nice schematic drawn up of v2.0 so I thought I'd post it. Also working on the installation instructions.

This is how the circuit board was designed, but I made the board so it's easy to modify the actual circuit for experimentation. So far I have had good results from removing Q2, but am trying a few other ideas as well. When I bypassed Q2 it seemed to improve the sharpness, but had less contrast.

As it sits, this mod works great, but there is some room for improvement in making the board smaller with fewer components.

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Edited by low_budget, Thu Mar 1, 2012 2:26 PM.

[low_budget]

I posted some screenshots using the latest v2 circuit as well as very basic installation instructions. It's actually kinda hard to write installation instructions for a system you don't own...

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Attached Files

•  a 8bit svid kit v2 install.rtf   5.58K   36 downloads

[vectormatt]

So is this the same board that is currently on eBay? or is there a later revision coming out soon?

[low_budget]

I have 2 different s-video mod boards.

v1.2 is for the Atari 5200 only. It is easier to install and smaller. It takes video signals off certain points on the A5200 board after going through some of the 5200's on board video circuitry. It has very good picture quality, but not quite as good as the v2.0

v2.0 is for the Atari 5200 as well as the 8 bit computer series. It is a complete video processing circuit and takes video signals directly from the GTIA graphics chip. Installation is trickier, as 6 pins of the GTIA need to be lifted which connect to the mod board. This board has better picture quality than v1.2, and am working on ways to improve it further.

I also posted a slightly different v2.0 schematic I have tested and had good results with. I bypassed Q2 and adjusted some resistance values in the Chroma circuit.

The s-video output for all the circuits I sold has been very high quality. I'm working on improving the composite video mostly.

I don't plan on making any new board revisions, as circuit changes can be made with the boards I have. My current v2.0 circuits use the below schematic. If I discover a change that makes it better, I will include those.

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[BillC]

low_budget, on Sat Feb 25, 2012 1:24 PM, said:

I tried two different configurations so far, the first was as designed and based on the Atari 800's circuit. This one had excellent contrast, but some color bleed.
In the second configuration I bypassed a transistor in the chroma circuit and connected pin 2 of the FMS6400 to ground. This made the color bleed almost unnoticeable. I'm happy enough with this version to offer for sale in limited quantities.
I don't have an Atari 8 bit computer, so I wasn't able to test on one. If somebody would be willing to give it a try and post some pictures, I would be willing to send them a free (bare) 2.0 circuit board.

Replacing the CD4050 with the faster 74HC4050 reduces propagation delay of the LUMA signal, which is supposed to help the color bleed issue.
The video circuitry of the Atari 8-bits(except the 1200XL with its color boost circuit) is very close to that of the 5200, you can see this by comparing the schematics, so the results should be basically the same.

[low_budget]

BillC, on Sat Apr 21, 2012 11:35 PM, said:

Replacing the CD4050 with the faster 74HC4050 reduces propagation delay of the LUMA signal, which is supposed to help the color bleed issue.
The video circuitry of the Atari 8-bits(except the 1200XL with its color boost circuit) is very close to that of the 5200, you can see this by comparing the schematics, so the results should be basically the same.

I realize I haven't updated this post in a while, but I did try a CD4050BE and a CD74HC4050E. I couldn't really tell much difference between the two. I did recently try buffering the chroma, and the 74HC4050 does seem a little sharper this way. I have tried removing the transistors and using the FMS6400 for amplification, but so far my efforts have failed. I think it could be done, but I may leave the transistors in so there is no loss of contrast.

I have sold several kits to Atari computer users, and feedback was positive. I did look over the video circuits of several 8 bit computer models and the 5200 when designing this circuit. There are actually many differences between some models. The 1200XL has 3 transistors in its chroma amp, the 800 has 2, the 5200 & 400 have one. The luma circuits also vary, the RF only models (5200 and 400) have resistance ladder values double what the other computers have. I'm guessing because the signals going to the RF modulator don't need much amplification.

I'm looking into making a "solderless" board that will plug into the Atari PCB and the GTIA will plug into the mod board. The output jacks and 5v supply will still need soldering. I've read on the Atariage forums 8bitdomain made something similar in the past but I don't know much about the actual mod.

Edited by low_budget, Mon Apr 23, 2012 3:42 PM.