Upgrade an Atari 400 to Composite Video with the Super Color CPU Card (1-2 hours)

Task: Upgrade an Atari 400 to Composite Video with the Super Color CPU Card

Needed: Super Color CPU Card and cables, soldering iron, Dremel or drill

Time: 1-2 hours

Introduction

The Atari 400 was my first computer. It is an aesthetically pleasing computer but limited by the membrane keyboard, 16K of RAM, and RF video out like the Atari 2600. Fortunately, if you love the 400, there is a relatively easy modification to produce composite video which can be converted to HDMI using something like the Retrotink for display on an LCD or LED TV via HDMI.

The Super Color CPU Card for the 400 was developed by Jürgen van Radecke (thank you!) and sold in the U.S. by Gavin Haubelt (thank you!) from the Vintage Computer Center. This magic comes from the inclusion of an Ultimate Atari Video (UAV) on the circuit board.

Instructions

This is a pretty easy mod which should take an hour or two or less if you have a workbench with everything set up and ready to go. This took me much longer because I ran into some problems with the main circuit board of my 400. Fortunately, I was able to move the mod over to another 400 and it worked great. It also took me a little time to get used to the 400 hardware which is very different from the 800XLs I have been working with.

The first step is to read the online instructions (PDF) created by Jürgen. These instructions are pretty good. Note the colors of the wires in the instructions at the time I did this mod did not match the color of the of the wires I received with the kit (more below). Also, the instructions don’t tell you how to get the composite cable out of the 400 (more below). Be sure and test your Atari 400 thoroughly before starting the mod as suggested in this document. Consider my instructions below as secondary or complementary to those provided by Jürgen. Hopefully a few of my tips will augment the mod process making it a little easier.

The second step is to navigate your browser to the Vintage Computer Center and order the Super Color CPU Card (SCCC) for about $85. You will receive the card, a composite video cable, and an audio cable. This mod requires three wires to be soldered.

The third step is the preparation of your workspace. You will need a soldering iron to connect three wires along with screwdrivers, needle nose pliers, etc. You will also need a Dremel or drill create a hole for the composite cable to exit.

The fourth step to disassemble the 400 case. Once you have removed the four screws from the bottom, flip the 400 over and remove the top. Note that the cartridge lid needs to be open to get it off! Lift the top of the case very gently as the keyboard ribbon is attached and will provide resistance. Gently lift the keyboard ribbon from the circuit board. Unlike the 800XL, this keyboard ribbon has delicate pins.

The fifth step is to remove the power board on the right side of the 400. You will first need to remove two screw on the left side of the power board. You will also need to detach the tan bar emanating from the cartridge door. This is what turns the Atari on when the door is closed. Remember the silver switch it connects to on the power board. We will use this switch later for testing. Once those are remove, gently rock the board back and forth to detach it from the pins holding it to the main circuit board. You will need to unplug the RF video cable from the power board to fully remove it. Set the power board aside for now.

The sixth step is to unplug the speaker from the bottom left side of the main circuit board. You can leave the speaker in the based of the case until reassembly.

The seventh step is to remove the main circuit board from the base. It should lift out easily as nothing is holding it the base at this point. Set the base aside until reassembly. You should now have the main circuit board in from of you with the metal Faraday case (i.e. RF shield) enclosing much of the board.

The eight step is to remove the Faraday cage. Flip the unit over and remove the screws holding the bottom to the top. Set the bottom piece and top piece aside for now. You will need the top piece in step 12 below.

Atari 400 Maine Circuit Board and Power Board with Labels
Atari 400 Main Circuit Board and Power Board with Labels

The ninth step is to remove the CPU card or board sticking up vertically at the rear of the circuit board. Gently lift it out of its socket. This card has the 6502 CPU, the ANTIC chip, and a CTIA or GTIA television interface adaptor chip. Gently remove each chip being careful not to bend any of the pins. I use a small flat tool to gently wedge them up from each side a little at a time and evenly. Plug in each chip in the appropriate socket on the SCC board. Take it slow and be careful not to bend any of the chip pins. Bent pins can be very frustrating and delay the project. The original CPU card with its chips is show below alongside the SCCC card where they are to be transferred. Note that the chip numbers are printed on the SCCC to assist with locating where they go. The ANTIC chip (C012296) shown top left goes in the middle socket of the SCCC. The CTIA (C014805) or GTIA goes in the left socket of the SCCC while the 6502 CPU (C014377) goes in the right socket.

SCCC and Atari 400 CPU Board
Original Atari 400 CPU Board with Chips (top) and SCCC card (bottom)

The tenth step is to set the jumpers (red tabs shown above) on the SCCC. The first jumper is shown in the bottom left and is needed to specify whether the video is PAL or NTSC. Mine is NTSC so the jumper is placed on pins 2 & 3. The second jumper is shown top left and is used for color inversion. It is open by default as shown. The final set of 5 jumpers is shown to the right. These need to be up on pins 1 & 2 for a 6502C “Sally” CPU or down on pins 2 & 3 for the 6502B CPU (this is what my unit has).

The eleventh step is to solder the three colored wires from the black audio connector included in the kit. Note that the current version of the instructions show brown, white, and black wires. These correspond to the red, yellow, and black wires I received. The figure below shows where to solder these wires.

Three Wires to Solder
Three Wires to Solder

The twelfth step is to connect the composite video cable to the SCCC. It is important to first pass the bare wire end of that cable through the hole in the left of the backside of the top piece of the Faraday cage. This is the only place for that cable to make an exit from the shielding so it can be fed out of the back of the Atari. Once it is fed through you can then connect it to the green terminal block with the six screws. You must loosen the screws several turns with a really small screwdriver. Feed the wires in in the order show in the instructions and below and then tighten firmly. The black wire is pretty thick and I needed some force to get it in. You can also connect the back audio cable to the three pins shown top right below. Note the flat side of the connector should be facing up.

Wire Connections on SCCC
Wire Connections on SCCC

The thirteenth step is to plug the SCCC board into the circuit board with the chips facing toward the back of the computer.

In the fourteenth step we will test the unit before reassembly. Reattach the power board by inserting it carefully over the pins. Do not screw it down yet. Attach the Atari 400 power brick and plug it in. Attach the composite video cable to an S-video cable and attached that to an HDMI converter such as the Retrotink. Attach an HDMI cable from your TV or monitor to the Retrotink. Power on the 400 while holding down the silver button on the power board that was attached to the tan arm emanating from the cartridge door. Use something non-metal to hold it down to avoid a shock. If all goes well, you should see the Atari 400 boot into Memopad in clear HDMI. Feel free to try a cartridge as well. When you are done unplug everything and remove the power board.

In the fifteenth step we will modify the bottom part of the Atari 400 case to make room for the composite cable to exit. I first tried to feed this through the RF cable hole but found it was long enough to exit from there. So, I used a Dremel to grind a hole in the top middle part of the bottom case (see below). This was pretty easy to do and I am very happy with the result. You can barely see the cable emanating from the Faraday cage whole through the slats just to upper right of the hole.

Composite Video Out
Composite Video Out

Finally, we are ready for reassembly. Insert the circuit board into the top of the Faraday cage. This is a little tricky since you need to make room for the composite cable. I wrapped it around the chips and out the hole. You will need to some patience to get this to fit back in cleanly and with the circuit board below the lip of the metal. Leave enough cable coming out of the shield so it can exit the case as shown above. Once in you can then replace the paper and screw the bottom piece to the top piece. Flip the unit over and reattach the power board and screw it down. Note that I removed the RF cable completely since I didn’t need it anymore. It simply unplugs from the power board. This make reassembly into the base little easier as well. Now reattach the speaker and the keyboard. I recommend removing the keyboard from the top part of the case before trying to plug it back in with the delicate ribbon connector. It is a little awkward and be careful with the pins. Once the keyboard is in it is easy to reattach it to the case. Reattach the top of the case remembering to open the cartridge door first. Close the cartridge door once the top is on and then seat it in the base. Flip the unit over and screw in the four case screws. That is it! Test it again for peace of mind.

Stock vs SCCC 400
Stock RF Video on CRT (left) vs SCCC with Composite Video Converted to HDMI on LED TV (right)

Comments

The mod itself is pretty easy. The hard part is getting the 400 apart and back together again. The Faraday cage makes this an awkward project and definitely took the majority of the time.

In addition to reading the provided instruction, you might also watch this video from FlashJazzCat for some additional info which might be useful.

I tested my 400 before I started the project and discovered afterward that the 400 was trying to boot from cassette when I powered it on. The video was working fine. I spent several hours trying to track down this bug and eventually moved the mod over to another 400 I had and it worked great. I never did figure out what the problem was. Thanks to Herb Shaltegger and Jimmy Fitzpatrick for their troubleshooting ideas and tips on Facebook.

If you love your 400 this is a great project despite the challenges!