The DIY Microcomputer from Yugoslavia

The Z80-based Galaksija dares to be different.

During the Cold War in Eastern Europe, computers had a poor reputation. At that time, there were attempts everywhere to replicate American IBM personal computers, British ZX Spectrum, and other Western computers. However, later came the Yugoslav Galaksija, a very inspired idea that brought computers to ordinary people.

Galaksija is an 8-bit homemade machine based on the Z80, designed cleverly using materials that Yugoslavs could import from Western Europe. During its brief heyday, thousands of these computers were manufactured, and commercially assembled Galaksijas entered homes and schools across Yugoslavia. Now, we can also try this assembled machine ourselves.

As a retro computer technology enthusiast, I saw a complete kit for Galaksija being sold on Crowd Supply at the beginning of 2022, so I habitually placed an order. It wasn’t until months later, after seeing Vlado Vince’s brilliant talk about Yugoslav computers at the HOPE hacker conference, that my interest was truly sparked. Due to ongoing delays in the delivery of the kit from Crowd Supply, the delivery time remained uncertain. However, I was lucky; in April 2022, I met Vince at the Eastern Retro Computer Festival, who gave me a Galaksija printed circuit board (PCB) and a link to a modern materials list. I felt ready to start, so I canceled the Crowd Supply kit order and began working on it myself.

In 1983, the complete plan for Galaksija was first published in an article in the computer magazine “Computers in Your Home” (Računari u vašoj kući). The magazine was co-founded by Galaksija’s designer Voja Antonić and editor Dejan Ristanović. (In 2018, the English version of the article was published by No Starch Press in the second volume of PoC||GTFO.) Yugoslavs who did not want to order parts from abroad could order them from Antonić and Ristanović.

Galaksija originally used a single-sided printed circuit board, but a few years ago, Antonić released a revised version with a double-sided printed circuit board. This basically eliminated the need for jumpers when soldering, greatly speeding up the assembly process. The new version also made two other adjustments, adding a set of video and audio connectors and including a capacitor to address timing issues with contemporary versions of the Z80 CPU chip.

However, even with these satisfactory adjustments, if you are under 50, you might find the making experience quite different. For beginners, many resistor values seem a bit off. Modern designs generally use multiples of E6 series ohm values, such as 1.0, 1.5, 2.2, 3.3, 4.7, and 6.8. But making Galaksija requires a set of E4 series resistor values, as many resistors in Galaksija are multiples of 1.8 or 6.2.

Next, like some other early home computers, Galaksija’s video circuit is minimal, relying primarily on the CPU to generate an analog TV signal. Although the increased computational load significantly slows down Galaksija, this was mainly to keep the cost of components within the legal import limits. Galaksija can generate European PAL TV signals, and I can connect the signal to a flat display, thanks to the RetroTink-2X Pro, a lovely box that can convert many outdated video signals to HDMI. You can also try plugging the signal into an old analog American TV, as its pure black-and-white signal is compatible with the NTSC standard, but I found that this requires a highly compatible television and skilled vertical synchronization control.

Cancelling the Crowd Supply kit order gave me a headache: Galaksija’s three read-only memory (ROM) chips come in two styles. These chips are erasable programmable read-only memories (EPROMs) that can be written electronically like modern electrically erasable programmable read-only memory (EEPROM) chips. However, to erase an EPROM, you need to expose it to ultraviolet light through a small round window on its package for several minutes.

Since the 1980s, I haven’t dealt with EPROMs, and under a junior science microscope, that EPROM was bad. I could find supplies on eBay, but I quickly realized that obtaining the chips was just the first step in a complex process. Like many manufacturers, I used a budget-friendly ROM programmer based on TL866. These devices do not provide the high voltage required to program EPROMs, although online hardware modification manuals claim it can be done. I even had trouble reading the chips to verify they were blank. Was it my toolchain that had issues, or was the problem with the chips themselves? If my Galaksija doesn’t boot, how do I know if the problem lies with the EPROM or the circuit board?

Faced with a series of lengthy debugging sessions and an impending deadline, I did the only logical thing—I cheated. I emailed Vince, who also lives in New York, and he graciously brought an EPROM eraser, a modified TL866 programmer, and some programmed ROMs for testing to the office. After two hours of debugging, including removing a useless chip, Galaksija finally displayed the READY prompt. Everyone should have an 8-bit Yugoslav DIY computer; you may not need it for many years, but when you have it, you will really be glad.

You don’t need to understand Serbian or Croatian to program Galaksija. It has a version of Basic used by the TRS-80 Model 1, with English keywords. Software saving and loading is done through an audio jack, originally intended for tape recorder interfaces; additionally, some Galaksija software is available for download, including classic software like Tetris. Although Galaksija may not be as famous as Western 8-bit computers like the ZX Spectrum or Commodore 64, it provides a great insight into how people elsewhere joined the digital revolution and how proactive engineering design can overcome significant obstacles.

Author: Stephen Cass

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