Nearly-Destroyed Commodore Gets New Life

We all have our shiny, modern computers for interacting with the modern world, but at times they can seem a little monochromatic. Even the differences between something like macOS and Windows for the average user often boil down to which operating system loads an Internet browser. There are obviously more differences than that, but back in the 80s it was much more extreme with interoperability a pipe dream in most cases. What keeps drawing people to maintaining and using computers from that chaotic era is more tangible compared to modern machines, and that is meant quite literally; computers from this era can be saved from an extreme amount of degradation like this Commodore that was nearly completely destroyed before it was re-discovered.

The first step was to restore the case of this Commodore PC20-III, but the restoration of the computer’s internals took a bit more time. First, the entire board was de-soldered, with any rare chips being set aside for future use. Unfortunately the board itself was too corroded and otherwise damaged to be used, but since these were just two-layer boards it could be photographed and then re-created in CAD software to make a near-perfect duplicate of the original. The team at [The Cave] took the opportunity to add patch wires which would have been present in the original machine into the PCB, and made some other upgrades as well like adding sockets to various chips that would have been originally soldered to the board.

The passive components, especially capacitors, were brand new as well and some period-correct components such as a monitor and keyboard finish out the build. The computer boots on the first try, and is quickly put through its paces testing the hard disk drive, using the old floppy drive, and even playing a few video games from the era. The fact that retrocomputers like these are easy (by modern standards) to reverse engineer and restore surely leads to their continued popularity, and we’ve seen everything from C64s to this 128DCR get a similar full restoration.

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Drop-In Switch Mode Regulators

Perhaps the simplest way to regulate a DC voltage is using a voltage divider and/or an active device like a Zener diode. Besides simplicity, they have the additional advantage of not being particularly noisy, but with a major caveat: they are terribly inefficient. To solve this problem a switching regulator can be used instead, but that generally increases complexity and noise. With careful design, though, a switching regulator can be constructed to almost completely replicate a linear regulator like this drop-in TO3 replacement. (Google Translate from German)

While the replacement regulator was built by [Mr. Floppy], the units are being put to the test in the linked video below by [root42]. The major problem these solve compared to other switching regulators is the suppression of ripple, which is a high-frequency artifact that appears on the DC voltage. Reducing ripple in this situation involved designing low-inductance circuit traces on the PCB as well as implementing a number of EMI filters on both input and output. The final result is an efficient voltage supply for retrocomputers which has a ripple lower than their oscilloscopes can measure without special tools.

[root42] is not only testing these, but the linked video also has him using the modules to repair a Commodore 1541 which originally had the linear TO3 voltage regulators. It’s definitely a non-trivial task to build a switching power supply that meets the requirements of sensitive electronics like these. Switch mode power supplies aren’t new ideas, either, and surprisingly pre-date the first commercially-available transistor although modern ones like these are much less expensive to build.

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Commodore CHESSmate Replica Runs On The ESP32

The Commodore CHESSmate chess computer might not be terribly well known, but that doesn’t make it any less worthy of being reproduced. If anything it is more important, as it gives more people an opportunity to use one of these devices, yet beyond a purely emulated experience the real user interface is harder to experience.

Internals of the reproduction Commodore ChessMate (Credit: Michael Gardi)

This is where [Michael Gardi]’s modernized replica provides a highly accessible version, consisting of a custom PCB with an ESP32 as the brains of the system. Although decidedly overkill next to the 6502 in the original CHESSmate, it makes the project far easier for others to assemble as it contains few components that shouldn’t be readily available.

The ESP32 is mounted on a small daughterboard which plugs into the main PCB with the buttons, LEDs and indicators. The whole stack is then inserted into the 3D printed reproduction case. These 3D models along with the ESP32 port of the CHESSmate¬†firmware can be found in the GitHub repository, along with a minimalist frame and a ‘CHESSmate Lite’ version as alternative enclosure options for those who somehow don’t appreciate the delightful 1980s aesthetics.

We covered the Commodore CHESSmate last year, including a highly faithful reproduction built by [Hans Otten], which [Michael] read the day after meeting [Peter Jennings], the author of MicroChess (which the CHESSmate uses internally) at an event at York University. Taking this as a sign, he set to work on this particular project.

We’re not sure if there’s really a cosmic force directing [Michael] towards his next project, but if there is, we’d like to take this opportunity to thank it for doing a fantastic job so far.

The Quaint History Of The Commodore ChessMate

The Commodore International of the 1970s was a company which dabbled in a bit of everything when it came to consumer electronics, with the Commodore ChessMate being a prime example of the circuitous way that some of its products came to be. Released in 1978, its existence was essentially the result of MOS Technology releasing the KIM-1 single board computer in 1976. In May of that year, [Peter Jennings] traveled all the way from Toronto, Canada to Cleveland, USA to attend the Midwest Regional Computer Conference and acquire a KIM-1 system and box of manuals for a mere $245. On this KIM-1 he’d proceed to develop his own chess game, called MicroChess, implemented fully in 6502 ASM to fit within the 1 kB of RAM.

As one of the first major applications to run on the KIM-1, it quickly became an international hit, which caught the attention of Commodore – which had acquired MOS Technology by then – who ended up contacting [Peter] about a potential chess computer project. This turned out to based on the custom MOS 6504 CPU, while sharing many characteristics with the KIM-1 SBC. Being a MicroChess-only system, the user experience was optimized for more casual users, with the user manual providing clear instructions on how to start a new game and how to enter the position of a newly moved piece, along with no less than eight difficulty settings.

If you’re feeling like making your own ChessMate, or want to dig into the technical details, this excellent article by [Hans Otten] has got you covered.

Top image: Commodore ChessMate Prototype in 1978. (Credit: Peter Jennings)

(Thanks to [Stephen Walters] for the tip)

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Hackaday Links: July 9, 2023

Good news this week from Mars, where Ingenuity finally managed to check in with its controllers after a long silence. The plucky helicopter went silent just after nailing the landing on its 52nd flight back on April 26, and hasn’t been heard from since. Mission planners speculated that Ingenuity, which needs to link to the Perseverance rover to transmit its data, landed in a place where terrain features were blocking line-of-sight between the two. So they weren’t overly concerned about the blackout, but still, one likes to keep in touch with such an irreplaceable asset. The silence was broken last week when Perseverance finally made it to higher ground, allowing the helicopter to link up and dump the data from the last flight. The goal going forward is to keep Ingenuity moving ahead of the rover, acting as a scout for interesting places to explore, which makes it possible that we’ll see more comms blackouts. Ingenuity may be more than ten-fold over the number of flights that were planned, but that doesn’t mean it’s ready for retirement quite yet.

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Commodore Floppy Drive Fixing Chaos

One of the best parts of retrocomputing is that you can obtain so many broken systems and peripherals for repairing and other assorted fun. This was the wholesome activity that [Drygol] embarked on recently with a gaggle of Commodore floppy disk drives that he obtained, involving a lot of cleaning, soldering, calibrating and other assorted entertainment. This follows cold on the heels of an earlier repair session of a stash of Commodore 1541 FDDs.

Testing Commodore FDD head alignment using the 1541 diagnostic cartridge.
Testing Commodore FDD head alignment using the 1541 diagnostic cartridge.

As with any such devices, the first thing to do is to clean the heck out of them, to remove forty-odd years of dust and other debris, followed by testing of functionality, replacing dead ICs and the usual round of (electrolytic) capacitor replacement. Retrobrighting gives it that fresh-out-of-packaging look, which leaves just the calibrating of these drives. This procedure is essential to make sure the read/write head is aligned with the tracks on the disks, and is the most fiddly part of the process.

What helps a lot here is the 1541 diagnostic cartridge by [World of Jani] that displays real-time information on the drive while you are tweaking its speed and head alignment. All you have to do is tweak the speed potentiometer, and adjust the position of the drive motor, which takes a bit of patience and a steady hand. After this repair session a few Mitsumi drives unfortunately remained dead due to busted coils. Despite a valiant repair attempt on the heads by manually rewinding the coils, this remains a topic for a potential part III.

Well Documented Code Helps Revive Decades-Old Commodore Project

In the 1980s, [Mike] was working on his own RPG for the Commodore 64, inspired by dungeon crawlers of the era like Ultima IV and Telengard, both some of his favorites. The mechanics and gameplay were fairly revolutionary for the time, and [Mike] wanted to develop some of these ideas, especially the idea of line-of-sight, even further with his own game. But an illness, a stint in the military, and the rest of life since the 80s got in the way of finishing this project. This always nagged at him, so he finally dug out his decades-old project, dusted out his old Commodore and other antique equipment, and is hoping to finish it by 2024.

Luckily [Mike’s] younger self went to some extremes documenting the project, starting with a map he created which was inspired by Dungeons and Dragons. There are printed notes from a Commodore 64 printer, including all of the assembly instructions, augmented with his handwritten notes to explain how everything worked. He also has handwritten notes, including character set plans, disk sector use plans, menus, player commands, character stats, and equipment, all saved on paper. The early code was written using a machine language monitor since [Mike] didn’t know about the existence of assemblers at the time. Eventually, he discovered them and attempted to rebuild the code on a Commodore 128 and then an Amiga, but never got everything working together. There is some working code still on a floppy disk, but a lot of it doesn’t work together either.

While not quite finished yet, [Mike] has a well-thought-out plan for completing the build, involving aggregating all of the commented source code and doing quarterly sprints from here on out to attempt to get the project finished. We’re all excited to see how this project fares in the future. Beyond the huge scope of this pet project, we’d also suggest that this is an excellent example of thoroughly commenting one’s code to avoid having to solve mysteries or reinvent wheels when revisiting projects months (or decades) later. After all, self-documenting code doesn’t exist.

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