Электроника МК-33 – modernity and archaism in one

There are cases in which a manufacturer releases a device that is already obsolete on the day of its release, lacking modern solutions. An example of such equipment may be the Soviet calculator Электроника MK-33 (Elektronika MK-33), but are you sure?

Calculator with dedicated carrying case

Электроника MK-33 is a Russian pocket calculator released in 1985, although I should write in 1978, because that’s when the model СЗ-33 (S3-33) prototype MK-33 appeared. The two devices are practically identical, it’s just that after 7 years of production the name and color of the keys were refreshed. The calculator, which reached me some time ago, additionally has the original case made of skai, which bears the proud inscription объединение (светлана) ленинград, which we can translate as Svetlana Leningrad Association.

The calculator, as befits a pocket device, is small in size, similar to today’s smartphones. The top of the case is made entirely of a single, stamped aluminum sheet, in which holes have been cut for the display aperture and buttons. The model designation, like the key descriptions themselves, have been applied directly to the metal, but they hold up quite well despite the passage of time. Unfortunately, the keyboard itself is of rather poor quality, the plastic buttons are hard and their stroke is small, so that you never quite know whether a particular key has been pressed.


The other part of the case is already the classic crisp Soviet plastic, in a color that used to be white. There was also a version with a black back. On the bottom there was a nameplate with the model designation – Электроника MK-33, serial number and date of production – March 1992. On the very top there was a battery socket cap.

Battery space

The calculator could be powered by three lead cells marked D-0.1 or D-0.125, each of which had a nominal voltage of 3V. Unfortunately, my copy does not have them.

Empty space after power socket

The second way to power the device was to plug it into a dedicated Электроника BP2-3S power supply. However, my calculator is devoid of a power socket, interestingly there is still a trace of the tape or sticker that covered the hole in the case. The reasons for the absence of the socket could actually be two – it could have been damaged and someone simply removed it, or it was not installed at the factory. I suspect that the second thesis is true, since since the early 1990s it was standard not to install a power socket.

Lead cell charger

Despite the lack of batteries in the pledge there is a charger for them. An interesting design that can charge all the cells simultaneously when plugged directly into an outlet.

Inside the charger

Since the whole thing is bolted together with only one screw, I decided to take a look inside, and after unsoldering two wires, you can see a minimalist circuit consisting of two stripped rectifier diodes and two 18k resistors.

Modernity and archaism

Comparison of Soviet and Japanese design

The Электроника MK-33 is a simple calculator that supports basic functions such as addition, subtraction, multiplication and division, but there were also a few novelties. This model was the first in the family of Soviet pocket calculators to receive support for changing the sign, percentages and operating on two registers. In addition, there were two versions supporting the 1/x or square root operation. It may also be interesting to note that it was in this model (the pocket calculator family) that the Russians used an LED display for the first time, while abandoning VFD tubes.

All this looks very good, but only from the perspective of the Eastern Bloc, when we look more widely, it is not so colorful anymore. Next to our hero today you can see the SHARP EL-208 calculator released in 1979, also the two devices are separated by a difference of only a few months. At a time when the Soviets were just transitioning to LED displays, devices from Japan were already running on liquid crystal displays still in use today. LEDs had long been in retreat. Besides, SHARP’s overall quality despite its age is still excellent, and the keyboard is no different from current calculators. In such a comparison, the device produced at the Leningrad Svetlana factory does not fare too well, what to say it was already outdated at the time of its release. The differences in technology can also be seen in the interior of both devices, but more about that later.

Interior of the Электроника MK-3 calculator

Электроника MK-33 after removing the casing

The device’s case is devoid of any screws and is held on by three latches – two at the bottom and one at the top. When removing the case, be careful of the buttons, which can fall out very easily; it is best to hold the calculator with the metal part of the case down.

The aluminum part included nothing but plastic keys and a display cover.

Black PCB cover removed

The first component that needs to be removed to get to the motherboard is the black plastic holding the display. It, too, is held on only by a few snaps.

Main board of the device

After removing the black plastic piece, the laminate can be safely removed. However, it is held on by two wires supplying power voltage from the battery socket. The motherboard itself is quite complex – there were two integrated circuits, an additional board soldered from the top, and the display.

SHARP and Elektronika calculator comparison

Having already seen the interior of the Russian calculator, one can compare it to the Japanese design. Well you can see quite a technological leap here, in SHARP’s calculator we have only one integrated circuit placed on a small PCB, this is impressive compared to the Soviet splendor.

Controls chip

The brain of the Elektronika MK-33 calculator is formed by two ICs – K145KT3P (right), whose job is to operate the display, and KR145IK16 – it manages the keyboard and performs all calculations. In the version with support for 1/x operation, the KR145IK16 module was swapped with the K145IK16. Both chips were surface soldered, and their enigmatic brown case color is also noteworthy.

It may be interesting to note that according to the “Information book on the content of precious metals in products and components of general industrial use. Approved by the First Secretary of the CPSU in 1985 and the Ministry of Defense of the USSR in 1986.” The K145KT3P and KR145IK16 chips contain 0.0241g and 0.00018g of gold, respectively.

Clock circuit

The task of the components on the additional board is to generate the timing signals necessary for the calculator’s operation.

Rarely viewed side of the display

The device was equipped with a nine-digit display, eight of which are used for digits and one is for the minus sign. The display was based on LED technology and resembles those used in Unitra calculators.

Problem with the plastic protecting the display

As I mentioned earlier, my copy of the calculator is devoid of both a battery and a dedicated power supply also, in order to get it working I decided to add and lead out the wires connected to the 9V battery.

After making such a modification and assembling the device, a problem came to light. It turned out that the condition of the translucent plastic leaves much to be desired. Unfortunately, it is so damaged that it is impossible to guess what digit is currently being displayed, so in order to carry out some tests, I had to remove the top casing.

Disadvantage of "negative zero"

Электроника MK-33, like many devices of the era, suffers from the problem of the so-called “negative zero”. Performing the 1-2+1 operation, we get a result of -0. Unfortunately, this is a design flaw of the KR145IK16 circuit and cannot be eliminated.

Exceeding the display range

An interesting behavior of the calculator can also be observed when the range of the displayed number is exceeded up or down. In the first case, the display will show a single minus sign, while when the number is too small, zero will be displayed.

Электроника MK-33 in its full glory

Well Электроника MK-33 is a very interesting device, you can say pioneering. New function, aluminum body, LED display used for the first time. Unfortunately, the modernity of the calculator ends when it crossed the border of the Eastern Bloc countries. Compared to Western designs, this calculator was outdated from the beginning, and its quality left much to be desired.


  • https://elektronika.su/all/elektronika-mk-33/
  • https://ru.wikipedia.org/wiki/%D0%AD%D0%BB%D0%B5%D0%BA%D1%82%D1%80%D0%BE%D0%BD%D0%B8%D0%BA%D0%B0_%D0%9C%D0%9A-33
  • http://www.arithmomuseum.com/album.php?cat=c&id=311&lang=en
  • http://www.calcuseum.com/SCRAPBOOK/BONUS/09183/1.htm

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