Building a Philips C52 (Magnavox Odyssey 2) Multi Cart

You can find lots more of this kind of stuff here https://www.youtube.com/8bitsinthebasement

Videos games are great fun, high resolution graphics, 7.1 channel sound, immersive 3D environments and online multiplayer gaming have all appeared in the last 20 or so years. At times we take it all for granted and don't spare a thought for the seeds that started it all, the source, the well where all gaming sprang from.

The first video game ever was a tennis game that was played on an oscilloscope, created by the Physicist William Higinbotham in October 1958 for the Brookhaven National Laboratory open house. In 1962 came Space war created by Steve Russell but could only be played by those who had access to a computer (not easy to come by in the 60s). Then in 1971 Nolan Bushnell and Ted Dabney created the first commercial arcade cabinet which housed a game based on Space war called Computer Space which became a huge commercial success and led to the founding of Atari, the company which gave us Pong and of course the Atari 2600.

A lot of consoles were made and thrust into direct competition with the Atari 2600 in the late 70s. One of which was the Magnavox Odyssey 2 (which was known under many other names across the world). I picked up a Philips branded one a few months ago, the "C52" and coaxed it into working again. I still had one problem though, I didn't have many games for it. So how could I get a taste of what this old console had to offer? Why, build myself a multi cart of course...

If you want to join the ranks of Ninja level Engineer and build yourself a Cartridge that contains loads of games for you to play on your Odyssey 2, or Philips C52 or whatever name it's going under where you live, then you better get studying, you'll need a high level degree in advanced mathematics and electronic engineering. Not to mention a doctorate in computer science from a world recognised bastion of higher learning like Cambridge or Harvard and all this even before you can consider starting into it. Or you could just do like me, and wing it...

If you're thinking of tackling this project I'd imagine that you have soldering equipment and know how to use it, so I won't go into any detail on that. Apart from a Philips screwdriver the parts you'll be needing are:

- a faulty or unwanted game cartridge

- a small piece of perf board

- a bank of DIP switches (I used a bank of 8 switches, you may not need them all)

- small gauge wire (I used wire wrap wire. Its easy to strip and very thin and light)

- 5-7 4.7K resistors (the larger the ROM chip you use the more of these you'll need)

- a 27 series EPROM chip (something along the lines of a 27C1000 will work well) and the pin out for the EPROM you've chosen

- a socket for the EPROM.

- Game ROM files (a Google search should see you right)

And finally,

- a programmer capable of programming the EPROM, or access to one as if all goes well you'll only be needing it for about 30 seconds ;)

Game cartridges for this system come in 3 different flavours. 2Kb, 4Kb and 8Kb. This means that in most cases a 2Kb cartridge can only be used for 2Kb games, 4Kb for 4Kb games and 8Kb for 8Kb games. But there are ways around this. However to keep things as simple as I can, in this instructable I'll be using a 2Kb cartridge with a set of 2kb games. Also I'll be using a M27C1000 EPROM for the build (but feel free to use any 27 series EPROM you have lying around).

You'll have to open that cartridge if you want to screw around with what's inside it. To do this firstly peel back the bottom left and right corners of the label on the front of the cartridge (use a hair-dryer to soften the glue if you don't want to damage the label). Underneath you'll find 2 cross head screws, remove them and gently separate both haves of the cartridge. Be aware that the metal PCB protector may spring out when you separate the two haves. It's worth noting that he PCB can be removed without opening the cartridge completely.

Now that you've liberated the PCB the first thing to do is remove the spring that's wrapped around the PCB and store it away safely. Next you need to remove the ROM chip that's soldered to the PCB. You'll be replacing that chip with a much larger one and a bank of switches to let you choose between all the different games you'll be flashing to your new EPROM. Use a de-soldering pump and braid to remove the chip and once you've done that you'll be left with a PCB that's ready to take any size EPROM you want to put on it.

The next thing you need to get to is making some satellite boards. Take two small pieces of perf board, one for the switch bank and another for the larger EPROM chip. I put these parts on their own separate boards so that they are easily movable and positionable when put back in the finished cartridge case.

Place your DIP socket in the perf board, solder it in place and then cut around it with a scissors or knife. Do the same thing for the bank of switches positioning the switch bank and a 4.7K resistor for each of the switches you intend to use.

Once you've made these, you have the three main parts (along with the PCB you've taken from the cartridge) needed to build your cart, all that's left to do is put them all together.

Wiring is the most time consuming step, it's also really important that all the connections be well soldered and that no shorts are made. I found that the easiest way to keep track of everything during this step was to use different coloured wire for each type of connection (this is invaluable for debugging afterwards, or in 6 months time if you decide to change out your EPROM chip for a larger one). I used GREEN for address lines, YELLOW for data lines, RED for 5V, BLACK for ground and PURPLE for everything else.

Using the pinout you downloaded for the type of EPROM you've chosen and the diagrams above wire address lines 0-10, data lines 0-7, CE, OE, 5V and GND from the PCB to the EPROM. Wire the remaining address lines from the EPROM to the switch bank. The switch bank also needs 5V on the resistor side and GND connection to the opposite side of the switches see the hand drawn diagram above.

Make sure you leave the wires long enough between the boards to be able to move the switch bank and ROM board around easily once the assembly has been placed back in the cartridge case.

When you've finished with the wiring double check that all the points are connected correctly and that no shorts have been made between any pins or tracks. When you're happy that everything's wired properly you can get to choosing some games to fill up that EPROM.

To some this is the most difficult step but it need not be. What this step involves is taking all the game files you want to put on the multicart (2Kb ROMs for the purposes of this instructable) and joining them together into one large file you can flash to the EPROM chip you've chosen in one easy step. So for example if you had a 27C128 you could put 8 X 2Kb game roms on it as this EPROM has a capacity of 16KB. With a 27C256 you could put 16 (it's a 32Kb chip) and so on.

NOTE : It is important to choose enough 2Kb roms to fill the EPROM chip you want to use.

Keeping this in mind make a folder on your Windows desktop (or Linux desktop) and call it anything you want then copy your 2Kb Game ROMs into this folder. Make sure that this folder contains just the 2Kb game ROMs you want to use and nothing else.

The next thing to do is open a command prompt and navigate to the folder you just made. From within this folder issue the command "copy /b *.* combine.rom" without the inverted commas and press enter. This should create a new file called combine.rom

If you're a Linux user open a terminal and navigate to the folder containing the ROMs and issue the command "cat *.* > combine.rom" without the inverted commas and push enter, this should generate a file called combine.rom.

No matter how you go about making it, the combine.rom file is simply all the game ROMs you placed in the folder appended together in alphabetical order in one rom file, and it's all ready to be flashed to your 27 series EPROM chip.

You're nearly there, it's time to put it all back together and play some games. Place the programmed EPROM in it's socket (making sure that you've put it in the right way around), place the metal spring back on the multicart assembly and put it all back into the plastic cartridge case. Mark the position of the switch bank on the plastic and drill and cut the case to allow the switches to protrude for easy access. I put some pieces of cardboard over some of the parts that had a tendency to move and rattle about inside the closed cartridge just to keep them in place. Replace the metal PCB protector and screw the cartridge case back together. If everything was assembled correctly and the EPROM programmed properly you should have a fully functional multicart. Place all the switches in the off position and place the cartridge in the console and power on. If it all went to plan you should be presented with the "SELECT GAME" screen, simply press 0 or 1 to start the game. You can use the switches on the cartridge to select any of the games you've programmed to the EPROM chip.

Games are selected as follows : each switch is given an ascending value 1, 2, 4, 8, 16, 32 and so on. If a switch is set to OFF then it's value is 0. Adding together the values of all switches that are set to ON selects a 2Kb memory bank. In the photo above, the second, third and forth of six switches are turned ON, so the value given is 14 (2+4+8) as counting using this system starts at 0 (all switches set to OFF) selecting 14 with the switches will in fact select the 15TH game that was programmed to the EPROM.

Note that a switch pushed down is set to ON and up is OFF (the "ON" marking on the switch bank should be ignored).

If the console behaves strangely when you turn it on displaying things like a flashing screen, scrambled display or just weirdness in general reset the console. If the strange behaviour persists turn it off and remove the cartridge. Check all your wiring to make sure that all points are properly connected and no dry joints or shorts exist. Another reason for a malfunctioning cartridge is an improperly programmed EPROM. Blank the EPROM and repeat the previous step "Programming the EPROM" from the beginning.

Earlier I said that cartridges came in three types 2Kb, 4Kb and 8Kb. You know how to make a cart that can run 2Kb games but what needs to be changed to play 4 and 8Kb ones?

Well the answer is very little.

Firstly if you look at the cartridge PCB you're about to convert you will find that "finger B" is joined to ground. Cut this trace. Secondly, connect address line A11 of the EPROM to "finger 13" of the cartridge PCB. All remaining address lines go to the switch bank. Now flash your EPROM with 4Kb games.

***For 8Kb do as for 4Kb but in addition join address line a12 of the EPROM to "finger 12" of the cartridge PCB. All the remaining address lines go to the switch bank. Program the EPROM with 8Kb games.

It is possible to make a multi-size multicart using toggle switches. If you wanted to be able to use both 2Kb and 4Kb games with your cart for example you would build a 4Kb version but join address line a11 of the EPROM to the toggle switch's centre pole. The switch's remaining poles are joined to the first switch of the switch bank and "finger 13" of the cartridge PCB.

The programming of the EPROM for a multi-size cart get a little complicated though. The multicart I made allows me to switch between 2 and 4Kb games and I programmed my 128Kb EPROM like this: Firstly I choose 32 2Kb games and combined them together into a file I called "2kbgames.rom". Then I choose 16 4Kb games and combined them into a file I called "4kbgames.rom". I then combined the 2kbgames.rom and 4kbgames.rom files I made into another file and flashed it to the EPROM. Now when the cartridge is set to 2Kb mode I can select games from 0-31. When it's in 4Kb mode I select the games from position 16-31.

***The 8Kb version should work in theory but I have yet to make it.

Thanks for checking out my first instructable, If this type of thing intrests you why not look me up on youtube. I make videos on moding, using and repairing old 8 bit computers and some consoles. You can find me here https://www.youtube.com/8bitsinthebasement