Wessi goes east: How I got to know the Robotron PC 1715

*Wessi [‘wes-see] is the flippant term for a West German citizen.

“With the production of the personal computer 1715 the VEB Robotron Büromaschinenwerk Ernst Thälmann Sömmerda makes an important contribution to the realization of the decisions of the XI party congress of the SED. By realizing the commitment of the office machine workers to provide the national economy with 10,000 personal computers in addition to the plan by the end of 1986, the acceleration of scientific-technical progress for the intensification of national economic processes and the increase of labor productivity is effectively supported.”

Source: Handbook “The Personal Computer 1715”, Publisher: VEB Kombinat Robotron, several authors, ISBN 3-349-00231-5, Issue: 1986/1987).

That’s how it was in the GDR back then! The leadership of the state power, the Unity Party SED of the German Democratic Republic, submitted a plan every five years in which it was determined what was to be developed and produced in the factories of the East German combines. Of course, the importance of computer technology was also recognized in the former Eastern Bloc, which included the then GDR, and so the company very soon began its own developments in this area.

As early as the mid-1950s, the first tube-based mainframes were created, and towards the end of the 1960s, with the development of the Type 300 mainframe on a transistor basis, the Robotron company was also founded. Later, this gave rise to, among others, the IT centers of the time in Dresden, Sömmerda near Erfurt and Mühlhausen in Thuringia.

First contact

However, the PC 1715 is not a home computer and therefore does not really fit into my collection. I was offered the computer by someone in the area who had saved it from being scrapped and couldn’t do anything with it himself. The computer originally came from a company liquidation in Sonneberg, Thuringia. Obviously it had been sitting in the basement for many years, because nobody had used it seriously for a long time. It survived the fall of the Berlin Wall relatively unscathed, but was then mothballed and forgotten for decades.

But now it has landed in a roundabout way with me! I found the idea in any case exciting to deal with this GDR technology a little more closely and would like to report my experiences with it.

The PC 1715 was manufactured from around 1985 in the state-owned combine in Sömmerda. It has an 8-bit processor, which was produced in the GDR under the type designation U880. The U880 is a clone of the Zilog Z80 processor, which was not allowed to be sold to the Eastern Bloc due to the embargo of the West. My computer is equipped with a total of 48 kB RAM and has two 5.25 inch floppy disk drives with 780 kB storage capacity each (older versions still used drives with a capacity of 624kB). A hard disk was not intended for this computer. However, the number of floppy drives could be extended by two externals. The operating systems available included SCP (Single User Control Program) or CP/A, which were compatible with CP/M developed in the USA by Digital Research. The CP/M operating system was, in simple terms, the forerunner of MS-DOS and was very widespread in the 1980s. It was adapted for many computer systems and due to its wide distribution the choice of software was very large. This software compatibility was also present with SCP on the PC 1715. The word processor WordStar was an example of one of the most widely used application programs that somehow found its way to the East and was also able to run on the PC 1715.

When I picked up the computer, I was able to try it out briefly on site. The seller didn’t have any floppy disks for booting, so I quickly created an SCP boot disk at home beforehand. This is not so easy nowadays, because the floppy format is not supported on modern PCs anymore. So I copied the image file I found on the internet to my Schneider AT 386SX running MS-DOS 6.22. There I connected a 1.2 MB 5.25″ floppy drive and used the MS-DOS tool IMD to write the image to a DS/DD floppy. In fact, the floppy worked in the PC 1715 right away, because after a few seconds a shifted image was displayed on the 12″ green monitor. By the way, the monitor is an integral part of the PC 1715. It is the model K7222.25, which technically corresponds to the model K7222, but has a housing adapted to the PC 1715 design. The monitor is connected via a GDR standard plug (EFS) and the power supply (12V) is provided by the PC’s power supply unit.

Keyboard with controller incl. U880 processor

The keyboard is similarly special. It does not have a western standard DIN connector either. Inside the keyboard sits its own U880 processor as keyboard controller. The very bulky keyboard has 98 keys and surprisingly, it doesn’t have a German QWERTZ layout, but the international typewriter layout (QWERTY). There are also considerably more function keys (15) than on IBM-compatible keyboards. The Enter or Return key, which is labeled “ET” here, has an unusual position next to the space bar, has the same height and is only twice as wide as the normal letter keys. Another interesting feature is the double-zero key in the numeric keypad, which speeds up the input of numbers with two decimal places, e.g. for prices.

I received two keyboards and two monitors with my 1715. Unfortunately, both monitors had their quirks. They turned on and showed a picture, but the picture position was strongly shifted – I suspected aging electrolytic capacitors. One monitor sometimes showed no image at all in the corners. One of the two keyboards was also defective. I.e. I had to deal with the convolute a bit more intensively at home. The most important thing was that the computer started from floppy disk. That is also not a matter of course after such a long storage.

Reconditioning

At home, I took a closer look at the computer from the inside. The PC 1715 has a very massive and stable steel case. The monitor’s case is also made of the same material. My model is in white-black, but there were also variants in a kind of brown/beige. What takes a lot of getting used to are the simple slotted screws that were usually used on computers from the GDR. I slipped more often with my screwdriver and often had to use it several times to loosen the screws. Inside, however, a very tidy picture presents itself after cleaning. The two floppy drives are already of newer Mitsubishi design and there is a single large, transversely mounted Papst fan in the center. Unusual: The fan works with 220V! So, it can’t be easily exchanged with a standard PC fan. When the computer starts, it spins up audibly. A quieter fan would be desirable here. The power supply is located on the right side and takes up the entire depth of the computer. As already mentioned above, it also supplies the monitor with power. Thus, only one power cable is necessary. The fan sucks the air from the front through the power supply and then blows it out through the plug-in cards and the mainboard on the left side, turned by 90°.

The power supply on the right, the Papst fan in the upper center, the floppy controller on the upper left, and the two Mitsubishi floppy drives below.

I opened the two monitors as well and found several pots for image adjustment. With a bit of trial and error, I was able to get at least one of the monitors back to providing a clean and reasonably stable image. In the meantime, I read a few reports on the Internet that didn’t give the monitors much chance of survival in the long run. Apparently the winding of the high voltage transformer is not of good quality and lets the monitors die sometime. A repair is then no longer worthwhile. Great, that’s a nice outlook! The keyboard membrane is also fragile and causes the keystrokes to either only work with higher pressure or to bounce. Fortunately, this is only the case with a few keys on my keyboard. By the way, there were several keyboard variants for the PC 1715. My model is the original variant with transparent function keys. One malady of the keyboard is that the keycaps come off quite easily and pop off along with the lift spring.

Since the computer was already open, I also cleaned the read/write heads of the floppy drives. As it turned out, the drives worked reliably and without any problems after the cleaning.

So, for the time being, it was possible to work with this setup and it made me happy that I could now take a closer look at the system.

Software selection and games

Unfortunately, it is no more so easy to find suitable software images on the Internet for this computer. Logically, the “community” for office computers of the GDR is not very large. It is easier to find software for the home computers or small computers KC85/87 of the GDR, for which there still seem to be many enthusiasts and collectors. Also with games it looks rather modest for the PC 1715. Except for a few ASCII character games you have to do without games, because the computer didn’t know raster graphics and even less sprites. Nevertheless I downloaded a few games and tried them out. Among them were such arcade classics as Wurmi, CatChum (PacMan), Ladder (DonkeyKong) or Super-Tetris. But I was most fascinated by the game Pilots, which very lovingly and with very clever tricks creates a great charm out of the ASCII graphics.

However, the computer was mainly developed for serious office work. The software for this was often cloned or pirated from very popular western program packages. As mentioned above, the SCP operating system was compatible with CP/M 2.2. This meant that corresponding CP/M software from the West could be run on the computer. The word processor TP for example was a clone of WordStar and the popular database ReDaBaS (Relational Database System) was a copy of dBase-II. Besides there were some programming languages like BASIC, Pascal, Fortran, Assembler.

Connections

There is only one free internal slot in the computer, which could be optionally equipped with a printer interface (IFSS), two V.24 interfaces, SCOM LAN, or a graphics expansion. The graphics extension in particular was so rarely used that it is now considered extinct.

However, the computer already has a V.24 interface each for printer and modem and the connection for the external drive unit on the back as standard.

Printing

Robotron K 6304 thermal transfer printer with roll holder for the “fax paper”.

An office computer without a printer is almost like a game console without a joystick 😉

I have been in possession of a thermal transfer printer robotron K6304 with V24 interface for some time now. It is very compact and does not even need a ribbon, because it works like a classic facsimile machine. However, it does require specially coated roll paper. Alternatively, thermal transfer ribbons can be used to print on plain paper. The only thing missing is a suitable cable, which connects the printer to the PC 1715. With its exchangeable interface modules, the printer can be used in a variety of ways. The V24 interface has a 25 pin serial connector. The connection to the computer is a bit more complicated to realize, because the printer port is a 5 pin GDR-EFS connector. Since the keyboard uses the same connector, I “borrowed” the connector from the defective keyboard and used it to assemble my serial cable.

Under SCP as well as with CP/M there is the copy tool PIP, with which one can also “copy” text files to the printer. With the command, pip lst:=textfile, the corresponding file is sent to the interface “lst”. The interfaces can be configured e.g. with the tool instscp menu guided. WordStar also uses the lst device by default, so that the printer also works immediately with the word processing software. Due to its thermal transfer printing method, the printer is pleasantly quiet.

Distribution

At that time, the PC 1715 was also exported to the Eastern bloc, i.e. the so-called brother states of the GDR as far as Russia. An additional EPROM slot made it possible to install a second character set, for example to make Cyrillic characters available. The character set could then be switched on the fly using a dedicated key on the keyboard. Due to its quite compact design and the compatibility to CP/M, the PC 1715 was widely used in the Eastern European countries. Together with its successor, the PC 1715W, a total of about 93,000 units were produced. Initially, the computer cost about 19,000 East Marks – later the price dropped to about 15,600 East Marks.

This computer could never be sold in the West, if only because of the license and patent infringements for the CPU, operating system and application software. In 1987, the successor PC 1715W was introduced, which had some improvements compared to the predecessor, such as 256 kB RAM and 4 MHz clock frequency. However, 8-bit technology was already considered obsolete at that time. In the same year, IBM introduced the PS/2 PC model with a 32-bit Intel 80386 processor, VGA, hard disk and 3.5″ floppy disk drive.