Title: DDR Robotron KC 87 Date: 20190702 Tags: retrocomputers ======================================== Since getting a Trabant[0], I've been interested in life in East Germany (DDR). Specifically with my interest in retrocomputing, I wondered what computing was like in that environment. I found a couple of relevant articles that were really fascinating. One article about the Stasi collecting information on computer clubs[1] and another about their UNIX history[2]. I've heard from several people is that there was access to smuggled Western computers like the Commodore 64. But there were several systems developed and built in the DDR. I ended up taking a liking to the Robotron[3] Kleincomputer (small computer) series. They are 8-bit home computers with a U880 CPU which is a Zilog Z80 clone at 2.5Mhz, 16K of RAM, 4 expansion ports, joystick connector, cassette connector, and black and white RF video output. It started out as the Z 9001 in 1984, then became the KC 85/1 then KC 87. Many expansion modules were produced, such as RAM expansion, applications on ROM, an EPROM programmer, printer and plotter interfaces, a disk drive interface allowing you to run CP/M, and other modules. It seemed to have interesting hardware and I really liked the aesthetics of this Robotron over other DDR produced computers. I was checking eBay and other German classifieds off and on for 9 months and this was the first Robotron Z 9001 series I've seen (and second Robotron anything). It was a Robotron KC 87[4][5]. It was working and even had 2 RAM expansion modules. It took about 2 weeks to arrive across the Atlantic, which I'm used to as I have to order parts for the Trabant from Germany, also. During that time, I had to figure out how I was going to power it. German mains voltage is 230V, but back in the 80's Germany and the DDR were only 220V. I had to find a step-up transformer to convert the voltage to ~230V. I wanted to be very careful not to fry my rare and historically interesting Robotron. Where am I going to get a replacement U880 CPU if I cooked it? I checked the output of the voltage converter with a voltmeter. 252V. Hmmm.. Most things can handle around +-10% of their rated input voltage. Seems this transformer is just within that +10% for the modern European 230V, but that's a bit high for the old 220V expectations of this computer. I reached out to a YouTuber I watch that restores old computers and other electronics and also happens to be German. Jan Beta[6] helped me confirm the history of German mains voltages and pointed out that the computer would probably be fine but might generate more heat so I might not want to run it like that for too long. I decided I would power the system up and test it for a minute but wouldn't leave it running for long until I found another power supply with the correct DC output or a way to reduce the voltage of the converter. Once the system arrived, I could see the video out socket was not something I recognized which I hadn't noticed in the eBay listing. Turns out PAL has it's own standard connectors that are different than what NTSC uses. I found the necessary PAL DVB-T to F-Type adapter on Amazon. Luckily modern TV's (which aren't usually as good as a CRT for retrocomputing) support NTSC, PAL, and SECAM standards. So once the simple adapter arrived, I was in business. The system booted up with no issues. BASIC is in ROM in the KC 87. Previous models needed it loaded from cassette. BASIC started and reported about 16K of memory. I hadn't plugged the expansion modules in yet. I popped the modules in expected them to be 16K each but BASIC only reported 32K total including the built in 16K. I posted my findings on Mastodon and someone quickly pointed out the obvious situation that the 2 modules were probably sharing the same address space. Sure enough, I opened one of the modules up (they are in plastic cases like game cartridges) and inside were a couple of dip switches. A few tries of combinations and I found a setting that gave me the full, elitist, decadent 48K. Turns out this was all documented (in German) in the manuals available online. Back to the power issue. I still didn't want to use the system for too long at one time. The solution I needed, as I discovered, is called a variac, or more generically, a variable auto-transformer. It's just a big slug of coiled wire and a giant knob to select where in that coil you pull the power from. Like a 10 pound dimmer switch for a lamp. I found a quality brand one used on eBay for less than a cheap Chinese new one. With it, I can lower the input voltage to the step-up transformer to lower it's output. I can get down to the Robotron recommended 220V just as the DDR intended. Perfect. I have a cable on the way that I should be able to use to connect to the cassette port. It's not an audio connector, it's a DIN connector the same as used for a Commodore's composite video. With the step-up transformer, the variac, adapters and cables, it's costing me more to run the Robotron than it did to buy and ship it from Germany. So what's this thing like? It's a very typical inexpensive home computer from the 80's. Although, it was too expensive for most people in the DDR so it was mostly sold for educational use. It has a terrible, awful thing they claim is a keyboard, as required for the era. The video is only black and white. A color module came later. There is a lot of office, design, and graphics software but I haven't found many games. Most computers from the DDR were not compatible with each other, even from the same manufacturer, so efforts to produce software were likely fractured. It does seem to be well built (aside from the ergonomics of the keyboard), made mostly of metal with plastic on the sides and for the covers. Overall, it doesn't compare to Western systems. It was behind the times on memory, graphics, and sound. I'm more interested in hardware and assembly programming than games so it's been great fun to learn about and I'm looking forward to doing more with it. [0] gopher://kagu-tsuchi.com:70/0/phlog/worst_car.txt [1] https://www.zeit.de/digital/games/2018-11/computer-games-gdr-stasi-surveillance-gamer-crowd [2] https://groups.google.com/forum/m/?_escaped_fragment_=topic/comp.unix.wizards/QX_dxElrVNs [3] https://en.wikipedia.org/wiki/VEB_Robotron [4] gopher://gopherpedia.com:70/0/Robotron KC 87 [5] https://photos.kagu-tsuchi.com/robotron/index.html [6] https://www.youtube.com/channel/UCftUpOO4h9EgH0eDOZtjzcA?pbjreload=10