Making Your Own Multi-Cart

So why would you want to make a multi-cart anyway? Well, to put all those fancy games you are writing using my makewave utility of course :)

Part I - The Supplies

You will need:

• 1 - Activision 4k Cartridge (e.g. Megamania)
• 1 - EPROM 27xxx (Design is for 27256, but can be adapted for others)
• 1 - 7404 Invertor
• 1 - Set of 3 dipswitches (come in multiples of 4)
• 3 - 1k resistors
• 1 - Perferated PCB (available at Radio Shack)
• 1 - Soldering iron
• Access to an EPROM burner

Part 1: Preparing the board

1. Remove the label from the Activision Game.

2. Unscrew the case.

3. Desolder the metal shield covering the PROM chip. (This step may not be necessary on all games).

4. Desolder the PROM chip. If you do not have a desoldering iron, then you should first cut all of the pins on the chip with a pair of wire cutters or a Dremel tool. Then heat up the pad with the pin in it, and when the solder is melted, quickly slam your hand against the table, this causes the solder and pin to fly out of the hole and usually leaves the hole free of solder. (Don't try this on your favorite table, it will ruin it!

5. Cut the three traces on the back side of the circuit board and the one trace on the front of the circuit board as indicated by the diagram.

6. Cut the circuit board along the line indicated in the diagram. The object is to allow for the insertion of a chip with more pins than the original PROM had. You could also accomplish this by drilling the appropriate holes and scraping away the large ground trace present, but cutting away this portion of the board is quicker and easier.

7. Cut out a piece of perfboard that is about as wide as the 27256 EPROM, and long enough to allow putting the 7404, resistors, and dipswitches on. An outline of this board is shown in the diagram. It is suggested that you get the prototyping board that has a small circular trace around each hole, that way items can be secured to the pcb. Radio Shack sells a board that is a good size and inexpensive.

8. Place a socket in the place of the PROM you removed, with the notch to the left when looking at the top of the PCB and the edge connector facing away from you. Please note that the diagram shows the bottom of the PCB, so the notch appears on the right. A socket is not necessary, and if it is not a very low profile socket, it will require you to cut a hole in the cartridge case. I suggest using a socket no matter what. If you have experience using a wire-wrapping tool, you can use a wire-wrapping socket, but be warned, some PCB's holes are not large enough for the wire-wrapping pins. I had to reem out the holes with a pick to get the socket in.

9. Along the row of socket pins farthest from the edge connector, place the perfboard you cut out in step 7. If you have the type with the circular pads around each hole, solder each of the posts to the board.

10. Wire-wrap or solder the wires indicated in the diagram, there are only about 11 wires to connect. For the 7404, you may use a socket, but do not have to because there are only 4 pins to use, it is easily desoldered if necessary. Make sure that the notch in the 7404 and socket are in the same direction as the notch in the socket for the EPROM.

11. Program the EPROM.

12. Place the chips in the sockets paying attention to the notches. You are done! There are modifications that will be necessary to reinstall this board back into an Activision case. Most notably, the relocation of one of the screwholes to hold the case together. Also, a hole may need to be made for the EPROM to stick through, and for the dip-switches to stick through. I will let you worry about this! I have progressed to put the dip-switches on the end of the cartridge, a far more convenient location.