Replacing the ROM in the Odyssey 2
The Odyssey 2, a video game from Magnavox circa 1978, is based on the 8048. The Odyssey 2 has everything you need for a general purpose computer. It has a full keyboard, removable program storage, and a display. I decided to replace the ROM with a programmable EPROM so I could start hacking around with the video and keyboard routines. The ROM in the cartridge is a 9316. This is virtually identical to the 2716. If you notice on the circuit board of the Odyssey 2 ROM cartridge, 21 is tied to 5+, and 18 is tied to ground. Pin 21 is VPP on the 2716, which you tie to 5+ anyway when you aren't programming it. Pin 18 on the 2716 is CS (active low), so this just means that the ROM is always selected. So, really, you can use a 2716 in place of the 9316. Now, I'm using a 2K EPROM. Since there are larger ROMs that the Odyssey 2 can use, you could certainly use larger EPROMS. 2K is a lot of assembly for me, and I don't expect to go much over that. When I use 2K well, I'll be happy. I also have many 2716 EPROMs around. OK. So, how do you go about replacing the ROM? Well, the first thing is to remove the circuit board from the ROM cartridge. There are two screws on the front of the cartridge towards the bottom as you look at the label. Unscrew these, and the cartridge will open. Of course, only do this with a cartridge that you are willing to destroy. This process is destructive. Please read this site's terms of use. The same goes for your Odyessey 2: you may destroy your Odyssey 2 if you mess with it using these instructions. I'm interested in this as a tool to understand and hack around with the 8048. Sure, I like the old video games as well. I spent quite a bit of time on Speedway today... quite enjoyable. Hey, my favorite all-time game is still Space Invaders (the arcade version). So many quarters lost to that game!! :) OK, after you remove the circuit board from the cartridge, you will see a circuit board like this:
It looks like the ROM has an 8131 date code? 31st week of 1981? Anyway, what you want to do is clip off the ROM:
Now, use a solder sucking tool/iron and suck out as much solder as you can from around the pins:
Pull out the pins one by one, and then suck out any remaining solder:
You can then solder in a low profile socket and use your own 2716 EPROM. The holes are plated through, so use lots of solder to fill up the pad through:
Check out the wide, curvy lines, the thick pads, and the nice mask. This game is made by a company used to producing radios and TVs. I suspect, as well, that these Odyssey 2 games will be around a *long* time. When you put the board back in to the Odyssey 2, the EPROM side of the board should face you. That is, the bottom of the board, solder side, faces away from you.
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