The Radio-86RK (Russian: Радио-86РК) is a build-it-yourself home computer designed in the Soviet Union. It was featured in the popular Radio (Russian: Радио) magazine for radio hams and electronics hobbyists in 1986. The letters RK in the title stands for the words Radio ham's Computer (Russian: Радиолюбительский компьютер). Design of the computer was published in a series of articles describing its logical structure, electrical circuitry, drawings of printed circuit boards and firmware. The computer could be built entirely out of standard off-the-shelf parts. Later it was also available in a kit form as well as fully assembled form.
Predecessors The Radio-86RK is the successor of earlier build-it-yourself computer of the same designers, the Micro-80, and has limited compatibility with it. Its description was also published in a series of articles in the Radio magazine in the early 1980s. But its complex design, consisting of several modules and containing about 200 chips, lack of printed circuit board drawings and most importantly lack of chips on sale made the assembly of the computer hard to accomplish. Micro-80 computers were assembled by only a few enthusiasts.
Assembly process To assemble the computer, it was required to acquire the necessary electronic components, to make two printed circuit boards and mount all components on them. It was mostly a single board computer, as the second board served only as the base to mount the keyboard keys. The main board used a single large connector for power, keyboard, tape recorder and even video output. Hence it was easy to disconnect the board and work on both sides of it outside the case. Next, the firmware had to be written in two erasable ROM chips using a chip programmer. Also a power supply unit, a keyboard and a computer case were to be made. The computer used a normal domestic TV set connected to a composite video input as a display. As most Soviet TVs of the time did not have video inputs, it was necessary to install a special module or modify the TV's electronics to implement it. The approximate cost of all required components was about 260 rubles. The circuitry of the Radio-86RK contained only 29 chips and was relatively easy to assemble. However, finding the chips to buy was difficult, as they were scarce and sold in small volumes in major cities of the USSR. It was particularly difficult to find the KR580VG75 video chip, which was produced only in small quantities. This led to the development of a replacement video circuit which contained 19 chips on a separate board, and was similar to the display module of the Micro-80 computer. The editorial board of Radio magazine received a large amount of mail in response to the publication. In almost every letter, readers noted how difficult it was to find the necessary electronic components. The editorial board published an appeal to the Soviet electronics industry, proposing they begin producing Radio-86RK kits commercially. By the end of the 1980s manufacturing of computer cases, keyboards and main boards for the Radio-86RK, as well as selling electronic components were carried out by numerous cooperatives.
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