Atari 5200 s-video mod and digital controller interface

Includes Atari 2600, Nintendo 8-bit, Sega Master System, MSX and more!

Moderator: Moderators

Post Reply
low_budget
Posts: 92
Joined: Tue Mar 30, 2010 3:21 pm
Location: Hell

Atari 5200 s-video mod and digital controller interface

Post by low_budget » Thu Oct 27, 2011 6:21 pm

I built an Atari 5200 s-video mod circuit by following this faq: http://www.atariage.com/5200/faq.html?SystemID=5200" onclick="window.open(this.href);return false;
I tested the modified Atari on a 20" CRT TV, it looked pretty good so I thought I'd sell it. It sold for $100 on ebay. I thought I should test it again before shipping, this time I used a newer LCD TV. It looked like crap, as bad as RF! So, do I cancel the sale because the buyer probably won't be satisfied, or do I figure out the problem. No, I need cash AND good feedback! I had to fix the problem.

I looked up the 5200's schematic, and found several errors in the s-video mod guide I used. Mainly, the point you pull the chroma signal from is mixed with luma. Yep, defeats the whole purpose of s-video. Also the luma outputs in the guide are labeled wrong but the resistor values were still correct.

UPDATE: I recently found that the 4 port system has slightly different component placement, R31 is moved to the left and swapped with R33. The chroma wire on these systems should be connected to the second last resistor in the row.

I got the picture looking much better by removing R31 (6.8k) and attaching the chroma line to the lower hole. Removing R31 will prevent the C from mixing with the Y. The new chroma line is connected to a 6.8k resistor in series then to the decoupling capacitor. I also found that adding a 1.5k resistor to ground after the isolated 6.8k resistor cleared up the picture.
The next step I thought was to design a circuit board incorporating the FMS6400 Y/C filter chip. I designed and built some prototype PC boards then assembled them. It took some tweaking, but now the s-video output looks great, and composite looks good also. Frogger had some issues with composite video, but all the 15 or so games I tested looked pretty good with the s-video.

I've recently finished v1.2 of my circuit board. It has several improvements over the original board:
0.4" shorter
improved layout with shorter traces
better power filtering for the FMS6400
rewired output of FMS6400 for less load on the chip

I'm now working on a S-Video circuit that will connect directly to the GTIA in the 5200 and Atari 8 bit computers. This circuit will be version 2.x and replace the entire video modulation circuitry in the system. I've used the Atari 800 schematics as reference and the initial board will be heavily based on that. I plan to improve it by making small changes one at a time from the original circuit.
One odd thing I've noticed, the luma mixing resistors on the 800 are half the values of the 5200.

I have also been experimenting with a better digital controller interface circuit than what I was able to find on the internet. I first tried a circuit using two 4052 chips, but couldn't get to output a stable resistance to the Atari. I then tried a DG413 quad analog switch and it's working great. This circuit has 1M pots to adjust the center point resistance (around 250k.)
Last edited by low_budget on Fri Feb 10, 2012 12:24 pm, edited 1 time in total.

low_budget
Posts: 92
Joined: Tue Mar 30, 2010 3:21 pm
Location: Hell

Re: Atari 5200 s-video mod and digital controller interface

Post by low_budget » Sun Nov 20, 2011 5:36 pm

I've been selling assembled and unassembled s-video mod boards for a couple months now and feedback has been positive. There's 2 versions, 1.2 which is cheaper and more basic, and v2.0 which completely replaces the Atari's video circuit.

After selling 3 prototypes of my 5200 digital controller interface, I designed new board and ordered 20. I now have a production version available, which looks pretty nice.

The keypad works nicely and has start, pause, & reset as well. Since the Atari 5200's controller ports are recessed, I can't find a deep enough DB15 connector to plug directly into the system. This adapter needs a Neo Geo style controller extension cable with all the pins wired.
Attachments
a5200 control v1_2 1.JPG
Newest controller interface
a5200 control v1_2 1.JPG (120.33 KiB) Viewed 3526 times
atari5200guideS.JPG
Corrected Solder Points for 2 Port Model
atari5200guideS.JPG (205.05 KiB) Viewed 3725 times
Last edited by low_budget on Sun Apr 15, 2012 9:53 am, edited 1 time in total.

low_budget
Posts: 92
Joined: Tue Mar 30, 2010 3:21 pm
Location: Hell

Re: Atari 5200 s-video mod and digital controller interface

Post by low_budget » Thu Feb 16, 2012 5:07 pm

I recently finished the latest version of both circuits, the v2.0 s-video mod and v1.2 of the digital controller interface.

Since the Atari 5200's Achilles heel is it's poor quality standard controllers and odd switchbox RF output, these circuits should be most useful to the Atari 5200 enthusiast.

The control interface is similar in function to a Masterplay, but has a built in keypad for convenience. It allows you to use a digital Atari joystick, Sega Master System pad, or Genesis controller with the Atari 5200. The v1.2 board has provisions to mount all components directly to the board for easy assembly. It uses a single DG413 quad analog switch and has potentiometers to adjust the centering point. Works flawlessly with games designed for digital controls. I plan to offer it for sale in kit form or fully assembled.

The v2.0 Atari s-video mod works with the Atari 5200 and 8 bit computers. It connects directly to 6 lifted pins of the GTIA and replaces the complete video circuit in these systems. It is currently being tested and I hope to offer assembled and unassembled kits after testing is completed.

ProgMetalMan
Posts: 257
Joined: Sat Feb 05, 2011 8:18 pm

Re: Atari 5200 s-video mod and digital controller interface

Post by ProgMetalMan » Thu Feb 16, 2012 6:37 pm

low_budget wrote:odd switchbox RF output
I don't get why people complain about that so much.
I have got an automatic one for my Genesis, although it doesn't carry power. But I still don't see why it's such an inconvenience.
ShockSlayer wrote:Proggy's right.
ttsgeb wrote:mfw prog was not only right, but 100% so.

Post Reply