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Atari S-Video Mod Kit for 8 Bit Computers and 5200 Game Console v2.1 Installation Guide

This is only meant to be a general guide and does not contain specific instructions for each Atari computer. I would not recommend attempting this mod yourself if you are inexperienced with soldering and multimeter use.

There are two options for installing the kit:

  1. Lift 6 pins of the GTIA graphics chip for connection to the mod board.
  2. Remove some components on the Atari circuit board to isolate the signals and make wire connections to the Atari board.

Note: The audio signal does not pass through the mod board, it needs only a 1uf capacitor.
The v2.1 s-video mod board has 3 connectors: input, output, and power. The pinouts are listed below from left - right.

6 pin input 6 pin video out 2 pin power
21 Chroma Ground +5v
22 Luma 0 Y - Luma (s-video pin 3) Ground
23 Luma 1 Ground  
24 Luma 2 C - Chroma (s-video pin 4)  
25 Sync Ground  
31 Luma 3 Cp - Composite (yellow RCA jack)  


1. Disassemble the system.

Different types of construction were used throughout the lifespan of the Atari computers. Early Atari computers have heavy aluminum RF shield and multiple boards that plug into each other. Later computers use sheet metal shielding and have most components on one board. Systems that have steel RF shield use lock tabs that must be twisted straight so the shield can be pried off. You may not have to completely disassemble the system, but you will need access to the graphics chip and the area where the video out jacks are to be mounted. It's best to plan out the installation before any mod work is performed. Make sure the board will fit where intended and wires can be routed without pinching. It may be more difficult to fit the board in early Atari computer models. If RF shielding is in the way, it is usually ok to discard if it is not a structural component.

2. Determine mounting location of the board.

The board should be mounted as closely to the GTIA chip as possible. This chip is grouped near the main CPU, POKEY, and ANTIC chips. On early multi board Atari computers this chip is located on the CPU board. This chip will have C014805 on it if it's a NTSC system or C014889 if it is PAL. Early 400 and 800 systems may have the CTIA chip, which is marked C012295 (untested but should be compatible.) The wires connecting the GTIA to the mod board should be short for the best picture quality.

3. Determine the location for the video output jacks and mount.

Near the mod board at the back is usually the best. Drill 1/4" holes for RCA jacks and a 1/2" hole for the s-video jack. Solder some lengths of shielded wire long enough to reach the mod board. Cut up RCA A/V cables work well for shielded wire. Regular wire may be used but have slight interference. S-video pin 3 is Luma (Y) and pin 4 is Chroma (C.) Pins 1 & 2 of s-video connect to ground as well as the outer shield of the RCA jacks. The jacks can then be installed and tightened.
The outputs may also be connected to the original monitor port on some Atari computers. If installing the kit this way you will need to look up the pinout and isolate the pins from the original Atari circuitry.

4. Locate the correct sound pickup point.

A typical Atari sound circuit is shown on the included POKEY chip diagram. Locate a spot on the board that is tied to pin 37, which will be where the 1uf capacitor is attached for the sound output connection (this will be done later.)

5. Locate a 5v power connection point and connect power to board.

There are many places to draw regulated 5v power. If you cannot locate one near the mod board you can tap off the power supply rail. Ground can be connected to any exposed area of the board's ground plane. 22-24 gauge wire is recommended for power connection.
On the Atari 5200, the bottom leg of R40 can be used for 5v.

6. Follow this step if lifting the GTIA pins. Otherwise skip to step 7.

Locate and remove the GTIA chip. It works best to carefully pry the chip with a micro flathead screwdriver a little at each side being very careful not to bend the pins. Using the GTIA chip diagram, carefully bend up the 6 pins until they are almost straight. Using small gauge wire, connect the straightened pins to the a 6 pin header receptacle in numerical order. Be very careful not to pull on the wires or the GTIA pins will bend. If they bend more than a couple times they may break! Carefully plug the GTIA back into the socket. Make sure the chip is orientated the right way and all remaining pins are going into the socket. Apply even pressure on each side of the chip. Make sure the lifted pins aren't touching anything on the board or each other. Skip to step 8.

7. Follow this step if the GTIA is soldered in or you prefer not to bend the GTIA pins.

Desolder and remove the CD4050 (16 pin IC near the GTIA.) Also remove five 1k pull up resistors that connect to the GTIA pins (pin 25 doesn't have one.) Use a multimeter set to continunity to locate the correct CD4050 pins connected to the GTIA. All but pin 21 are connected here. For the pin 21 connection a 10pf capacitor or 3.3k resistor will need to be removed (whichever component connects to GTIA pin 21.) This is where pin 21 will be wired. Wire these points to a 6 pin header receptacle in numerical order.

8. Wire the video and audio output jacks to mod board.




Use the above pinout for correct wiring to mod board. Use the included 1uF capacitor for the audio out connection with the negative end connected to the center of the RCA jack and the positive soldered to the audio point you found earlier on the Atari board. Plug the GTIA connector into the mod board and make sure the pin connections are correct.

 

9. Mount the mod board.

A good location is on top of a 40 pin IC or in a bare spot on the board. Use velcro or double stick tape depending on preference. Make sure the board is insulated from surrounding components and secure. Check for pinch points in the wiring.

10. Test and re-assemble system.

I would first recommend assembling just enough of the system to test it safely. Before plugging in the system check all input, output, and power connections carefully. After powering up the system check the picture, sound, and colors. Some adjustment of the color delay potentieometer may be needed if the colors seem off. Re assemble the system if everything checks out ok.

Rev 5