Building a Brand New C64
Playing Impossible Mission on a Commodore 64 built entirely from new parts is an almost possible mission.
To this day, the best selling single computer model of all time is the Commodore 64. Yes, you heard that right — in the 28 years since this classic computer was discontinued, even with the proliferation of home computing in more recent decades, no computer models have outsold it. Given the tremendous popularity of this computer, it is little wonder then that a thriving community of collectors and hobbyists still exists for all things Commodore. But with these computers out of production for all these years, and with the original models continuing to age, Commodore 64 computers, and replacement components, are growing more difficult to come by.
Considering the bleak prospect of a future with ever fewer Commodores, YouTuber The Retro Shack wondered whether or not it would be possible to make a Commodore 64 with all new components. What he found is that it is almost possible, but with some fairly significant caveats. If you want to spend some time saving humanity from an atomic inferno in Impossible Mission, you will still need to locate a handful of original Commodore chips.
To recreate the classic, The Retro Shack started with a motherboard design that he found freely available in PCBWay’s project library and had the PCB manufactured. This design is an exact copy of the original revision B of the board. He already had an original C64 “breadbin” style case on hand to use for the build, but noted that a number of reproduction cases are currently available for sale.
To save the time and hassle of tracking down all of the individual components, a complete (well, almost complete) Commodore 64 parts kit was ordered from Retro 8bit Shop. This supplied the logic ICs, RAM, capacitors, diodes, and well, pretty much everything. It only lacks the custom Commodore ICs. It is still necessary to track down the 6510 CPU, 6526 CIA, 901275 character ROM, 901226 BASIC ROM, 901227 kernel ROM, and a few others.
The Retro Shack had most of the original chips on hand, but did swap in a few modern replacements. The much-loved 6581 SID chip that gives the C64 its distinctive audio capabilities was replaced with the ARMSID. Similarly, modern replacements were also substituted for the PLA chip and the RF modulator. Modern replacements are not always a bad thing — the modulator replacement gives the system much crisper, clearer video output than was ever possible on the original.
With all the parts accounted for, the next step in the process is to solder all of the components to the main board. The Retro Shack also takes the precaution of testing resistor values (rather than trusting the labels) before soldering them down. This may seem like excessive precaution, but when dealing with a complicated circuit like this, finding a problem up front can save a lot of debugging time later. A few minor issues were encountered during assembly, for example, the joystick connectors supplied with the kit do not fit on the revision B board. Grabbing a few spares from the parts bin set the build back on the right track.
When the system was turned on for the first time, the result was… well, nothing. That is not entirely unexpected for such a large circuit, so it was time for The Retro Shack to get busy debugging the circuit. The initial problem turned out to be a failure to ground the video modulator board and set a jumper. After fixing that, the display came to life, but with garbled text. This is usually a bad character ROM, so that was checked, and in the process it was also discovered that a 901226 chip was socketed where a 901225 should be. After correcting these issues the beautiful blue C64 startup screen appeared, and the system passed all tests in a diagnostic cartridge.
While it is not possible to build a C64 from entirely new parts, you can get pretty close. That is good news for keeping Commodores running well into the future. The Retro Shack did not mention exactly how much the new(-ish) C64 cost, but after looking into a few of the components, it seems safe to say that you can get an original from an auction site for less money. So at this point in time, if you just want a C64, you might be best off going that route. However, there is something to be said for assembling your own that will appeal to many hobbyists regardless of the cost.