Like many of you old CoCo users out there, I’ve longed for better hardware and more memory. Recently, I downloaded Paul Barton’s 512k schematic from coco3.com and decided to build the circuit. The motivation for the project came from cloud9tech.com, but due to the notice on their website, I felt my time would be better spent building the upgrade as opposed to waiting for them to do it and ship it. The success of my project came from the documentation on how to install their upgrade, which I assumed was very closely related to Paul Barton’s board.
I began by purchasing a perfboard with solder points from Vetco Electronics, here in Bellevue. Next, I ordered the 30 pin SIMM sockets from Jameco electronics online. The SIMM modules were in a bag of old 486 parts I had in storage, and luckily for me, there were 4 of the 9 chip modules. I measured the board for the SIMM sockets and cut it with a butter knife (I’m low on tool resources as I’m in the process of moving) and a spiral saw bit on my dremel. Then I mounted the wire wrap strip-posts in the appropriate locations. I guess I got lucky with the parts, because everything lined up and the board could be easily inserted/removed from the CoCo3 memory expansion headers.
Not having any way to manufacture an etched circuit board, I decided that wire-wrapping was my best option, which took the better part of the weekend. After many blurry, crosseyed moments and near burns from the soldering iron, I completed the expansion board. Double checking the wire-wraps took about 4 hours, but I verified them by visual cross reference with the schematic, and then with a volt meter to make sure all the connections were good from the expansion headers to the SIMM module pins. Again, another stroke of luck, because not one wire was misplaced! I hope your projects go as smoothly as mine did!
Once the board was tested and the memory modules were snapped into place, I nervously mounted the board in the machine and connected the power. Nothing. Nada. No Disk Basic screen to greet me. In fact, I seemed to be pushing the GIME chip into some rather bizarre contortions, as the poor machine attempted to do something with the electricity I was giving it. Alas, I nearly gave up when I happened to remember reading something about cloud9tech.com’s install directions. And yes, there it was, on the last page: remove the existing memory and bust out 2 filter caps. Easy! Once I removed the memory and the offending capacitors, I plugged everything back in and – voila! My heart jumped at the familiar psychedelic cursor and disk basic welcome message! Success! All my years of failed analog projects, burned IC’s and smoking resistors had paid off in a resounding success.
Included you will find pictures of the memory expansion board. There is one note of caution that I will try to pass on: make sure to measure correctly! While my board may fit horizontally, the memory is too tall and prevents from fitting. Seems like my next project will be to mount everything in a mini-tower PC case. Mod central, here I come!
I hope you enjoyed reading my article, and hopefully I’ll have many more experiences to share with the growing revival of this wonderful little machine.
I’d also like to recommend that you purchase a copy of Portal-9 from Roger Taylor at coco3.com. The IDE is great, and the CCASM support is outstanding. I highly recommend the 6809 for anybody who is interested in learning micro processor programming and assembly language.
Matthew Potter
matthew@synapseware.com
