Robotron 1715

[Rosita Westhouse]

ThePC 1715 was an office computer produced by VEB Robotron in East Germany starting in 1985. The system featured an 8-bit microprocessor, the U880, a clone of the Zilog Z80. It was built for office work and education, but was also put to some specialist uses, for example an optional interface was available for controlling a pacemaker.[1] The 1715 had minimal graphics and sound capabilities. The price was 19,000 East German marks.

In contrast to the A5120 predecessor, the PC1715 was not built around the K1520 bus standard. There was no back plane, but the main board had 2 58-pin connectors that were largely K1520 compliant, with some signals omitted and replaced with custom internal signals. The floppy controller of the PC1715 used one of those internal bus extensions and was built with discrete components and logic chips, whereas other robotron computers of the 1980s used a clone of an Intel 8272 Floppy disk controller. The floppy controller board clearly appears to be based on the one used in the A5120.

A second U880 processor was used in the keyboard, together with a small firmware ROM to decode the keyboard matrix and transmit the keycode via a serial link to the main board. Though it was common practice at the time for processors that failed normal quality tests to be reused with much reduced clock frequencies and this may have been the case here.

The next step, is repairing Robotron 1715 K7222 monitor. Initially, I tried to plug in the monitor to the computer and see what happens ( probably a bad I idea ). After turning it on, I saw no signals that the monitor is heating, so the first thing to investigate was is there any voltage from the power supply applied at all. After opening monitor case I found that fuse was ok, but really corroded. I have removed the fuse and the fuse holder had no continuity due to corrosion. In my junk box I found another fuse holder and replaced it.

After a second try to power it up with a new fuse holder, I heard some crack and magic smoke. Usually it is not a good sign ? After further inspection I found that flyback transformer has huge cracks on it, not good.

Then started winding the flyback transformer coil. I made a jig for that: bench vise, drill, corc, a couple of magnets, and old phone with a magnetic counter app. You can get the picture from the picture ?

After testing without the outer coil, I noticed smoke in resistor R12. I guess the voltage is too high on it. tested resistor V3, it seems to be ok. Another guess is signal IS that goes to resistor V3 is too high.

Der PC 1715 ist ein Desktop-PC, dessen Gehuse 50 cm breit, 40 cm tief und 14 cm hoch ist. Gehuse, Monitor und Tastatur wiegen zusammen 12,8 kg. Die separate Tastatur besteht aus 98 Tasten gem der international standardisierten QWERTY-Tastaturbelegung mit einem zustzlichen Ziffernblock sowie 15 Funktionstasten. Zur visuellen Darstellung dient ein Grnmonitor mit den Auflsungen 6416 oder 8024 Zeichen. Es gibt keine Rastergrafik. Der Rechner hat keine Festplatte, dafr jedoch zwei eingebaute Diskettenlaufwerke, die um zwei externe Diskettenlaufwerke erweitert werden konnten. In der Praxis verwenden die Benutzer ein Laufwerk fr die Software und das zweite zur Speicherung der Daten. Als Software lieferte der Hersteller eine auf die Hardware angepasste Version des Betriebssystems CP/M unter dem Namen SCP. Alternative Betriebssysteme waren BROS und JAMB zur Kompatibilitt mit einem russischen Rechnersystem. Als Textverarbeitung lieferte Robotron TP, ein Duplikat von WordStar. Fr die Anwenderprogrammierung standen die Programmiersprachen BASIC, Pascal, Assembler und Fortran sowie das Datenbanksystem Redabas (eine dBASE-II-Kopie) zur Verfgung.

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, Smmerda near Erfurt and Mhlhausen in Thuringia.

The PC 1715 was manufactured from around 1985 in the state-owned combine in Smmerda. 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.

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.

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.

Robotron 1715 je přmm nstupcem počtače Robotron A5120, s kterm byl plně softwarově kompatibiln. Je založen na procesoru Zilog Z80 (na vchodoněmeckm klonu U880). Operačn systm se zde použval SCP (klon CP/M) nebo UDOS (klon Z80-RIO). Měl minimln grafick a zvukov možnosti. Obsahoval 64 kB operačn paměti RAM a procesor byl taktovan na 2,5 MHz. Jako ložn prostor složily dvě 5,25 disketov jednotky. Pro zobrazen se použval monochromatick monitor. Cel počtač vžil okolo 13 kg (počtač, klvesnice, monitor).

Jednalo se o široce použvan počtač pro kancelřsk a vzdělvac čely. Byl velmi robustn a spolehliv. Přes rozhran se k němu dala připojit extern 8 FDD mechanika. Takže se dal použvat pro čten/zpis na 5.25 i 8 disket. U monitoru často odchzela VN cvka. Ta se měnila na originln dl, kter je dnes už bohužel nedostupn. Odhaduje se, že celkově bylo vyrobeno přes 93 000 ks tohoto počtače.

The Robotron PC 1715 was a Zilog Z80 based CP/M machine produced in East Germany in the mid-eighties. It was used mainly asoffice and educational computer. As many Eastern European computers of the time, it was mainly made with elementary TTL logic, asthose parts were more readily available in the EastBloc countries.

The machine had no sound or graphics, but there are some prototype graphic mode expansion cards floating around. The first PC1715's were equiped with 360K/400K disk drives, but later versions were shipped with a single 800K drive.

The Z80 quickly became popular in the personal computer market, with many early personal computers, such as the TRS-80 and Sinclair ZX80, using the Z80 as their central processing unit (CPU). It was also widely used in home computers, such as the MSX range, SORD, and the Amstrad CPC, as well as in many arcade games. Additionally, it was also used in other applications such as industrial control systems, and embedded systems. The Z80 was widely used until the mid-1980s, when it was gradually replaced by newer microprocessors such as the Intel 80286 and the Motorola 68000.

The Z80 microprocessor was developed by Zilog, a company founded by Federico Faggin in 1974. The Z80 was released in July 1976, as a successor to the Intel 8080. It was designed to be fully compatible with the 8080, but also included new features such as an improved instruction set, more powerful interrupts, and a more sophisticated memory management system.

The Z80 quickly became popular in the personal computer market, with many early personal computers, such as the TRS-80 and Sinclair ZX80, using the Z80 as their central processing unit (CPU). It was also widely used in home computers, such as the MSX range, SORD, and the Amstrad CPC, as well as in many arcade games. Additionally, it was also used in other applications such as industrial control systems, and embedded systems. The Z80 was widely used until the mid-1980s, when it was gradually replaced by newer microprocessors such as the Intel 80286 and the Motorola 68000.The design was licensed to Synertek and Mostek as well as the European SGS.

The Z80s instruction set is binary compatible with the Intel 8080, so that 8080 code such as the CP/M Operating System and Intel's PL/M compiler for the 8080 can run unmodified on theZ80. The Z80 had many enhancements over the 8080 such as 16-bit data movement instructions,block copy and block I/O instructions, single bit addressing of all registers, IX/IY offsetregisters, better interrupt system and a complete duplicate register file for context switching during an interrupt.

Before the introduction of the 16Bit microprocessors in the GDR, there was theCP/M operating system, which was called DDR SCP there, widely spread for thesmall commercial data processing. The PC 1715 has a very high quality and hasthe typical 70s lacquer style.

It is interessesting that although normally the EVP(retailing price) wasimprinted, this was not the case for any computer: This is perhapscomprehensible for the PC 1715, because it probably did not belong to theconsumer goods. The EVP isn't even imprinted on a box of the LC 80 and noteven on the one of the SC-2 chess computer.

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