Sony SOBAX ICC-1500W Electronic Calculator

The Sony SOBAX ICC-1500W is a good example of Sony's second generation of electronic calculator. Sony's first generation calculators (such as the Sony ICC-500W) were built using hybrid transistorized circuitry and acoustic delay lines for register storage, while the second generation machines like the machine exhibited here were built using early small-scale integrated circuit logic manufactured by Sony. These integrated circuits contained a few gates or a couple of flip flops in a small plastic package. While the level of integration was pretty low, it was a major improvement in component density over the earlier hybrid circuit modules, allowing the calculators to shrink in size, and increase in capability. The use of IC technology also allowed the working registers of the calculator to be implemented in electronic registers (flip flops) rather than requiring a complex and somewhat temperamental acoustic delay line needed in the earlier Sony calculators.

Sony had been interested in the electronic calculator business as early as 1964, when they showed a prototype electronic calculator called the MD-5. But, for whatever reason, it took Sony another three years before they debuted their first production electronic calculator in 1967, the ICC-400W. Shortly thereafter Sony announced enhanced versions of the 400, adding accumulators and memory registers (ICC-500W, and ICC-550W), and somewhat later, a one-key square root function (ICC-600W). All of these first generation machines used Sony's hybrid transistorized circuitry and acoustic delay line register storage. Sometime in 1969, Sony introduced its second generation calculators, with these machines using Sony's own small-scale integrated circuit technology. Later, Sony moved into its third generation, which included higher-end programmable machines based on their small scale IC technology, with machines such as the Sony ICC-2550W. Sony also made a brief foray into the use of Large Scale Integration devices in a line of smaller desktop calculators, however, the market for calculators was changing very quickly, and by 1973 Sony management decided that calculators weren't the profit maker that they used to be, and they left the calculator market.

As with just about everything made by Sony, the 1500 is built to last. While not built to quite the nearly military-spec standards of the first generation Sony calculators, the 1500 definitely exudes a strong feeling of quality about it. Quality construction is used throughout, from gold-plated edge connector fingers, heavy-gauge sheetmetal chassis components, high quality cabinetry components, and an internal design that made serviceability a priority. It was clear that Sony was out to maintain their high quality standards in the design of their calculators, even when, at the time, consumers in the calculator market was more focused on pressuring the manufacturers to lower the price of entry for electronic calculators. These pressures forced a number of early calculator manufacturers out of the market by the mid-1970's.

Sony Sobax 1500 Opened Up

This calculator was made in the early part of 1970, based on date codes on the integrated circuits in the machine. At about the time this machine was made, Japanese calculator maker Sharp, in conjunction with the American electronics firm Rockwell (who helped design and manufacture the Large Scale Integration (LSI) IC's used), had just introduced an electronic calculator that used LSI circuitry. With a scant five 'chips' making up the Sharp calculator, it was much smaller, and significantly less-complex to manufacture than calculator designs based on small-scale integrated circuits like the Sobax 1500. The Sharp QT-8D shattered the price and size barriers that were in place at the time, and forever changed the marketplace.

Closer View of Sony Sobax 1500 Keyboard

The Sobax 1500 is a fairly basic 12-digit, four function calculator with memory. The calculator operates with fixed-point decimal location, with a rotary switch on the front panel of the machine selecting the decimal point location, at 0, 3, 6, or 9 digits behind the decimal point. This selection of decimal point settings is rather strange -- it is missing a selection for two digits behind the decimal point, commonly used for currency calculations. The 1500 uses arithmetic logic for addition and subtraction (like an adding machine), and algebraic logic for multiplication and division, with an "=" key used to finish off such calculations. The "C ALL" key clears the entire machine (including the memory register), and the "C ENT" key clears just the display. The 1500 has a constant function that operates in multiplication and division by virtue of a push-on/push-off key labelled "K". It also has a single store/recall memory register, with an "M IN" key storing the content of the display in the memory register, and the "M OUT" recalling the memory register to the display. The calculator also has an additional special-purpose accumulator that provides a "totalizing" function (activated by a push-on/push-off key marked "T") which causes automatic accumulation of the results of multiply and divide operations. The operation of the totalizing function is unusual, and warrants some explanation. Pressing the "T" key locks the key down, causes a "T" indicator to light at the right end of the display, and clears the total accumulator. While the "T" key is activated, any multiplication or division operations will have their result automatically added into the total accumulator. When the "T" key is again depressed (releasing the key and extinguishing the "T" annunciator) the content of the total accumulator is immediately recalled to the display.

The Sobax 1500 had a stable-mate machine, which was introduced a few months after the 1500, with a retail price around $150 less than the 1500. While virtually identical to the 1500 in terms of size, design, and logic, the lower price is a reflection of the huge pricing pressure in the electronic calculator market of the early 1970's. The Sobax 1600 provided automatic floating and fixed decimal rather than the fixed only logic of the 1500, and added a round-off feature, which proved useful to business users.

Like so many calculators from the late '60's and early '70's, the Sobax 1500 uses Nixie tube displays. In a bit of a departure from Sony's typical use of their own components, Sony opted to purchase the Nixie tubes used in the 1500 from Hitachi, with twelve CD-79 Nixies making up the display. The Nixie tubes are driven by discrete transistorized decoder/driver circuitry. The entire display assembly is contained on a circuit board that connects into one of the three main logic boards with a hand-wired cable. At the left end of the display panel, two annunciators exist, consisting of individual neon tubes lighting up through cutouts in the shape of "*" and "-". The "*" indicator lights when the calculator overflows or if division by zero is attempted. The "-" indicator lights up to indicate a negative number on the display.

The Display Circuit Boards

The main logic of the calculator is contained on three plug-in circuit boards, approximately 9" by 7" in size. The boards are made of a high quality phenolic material, with plated-through holes and gold-plated edge connector fingers. The boards have a green solder-resist, and high-quality silkscreened component identification information. The top-most board contains the display driver subsystem piggy-backed onto it, along with some IC logic (likely the display register and data path circuitry), and an area of dsicrete components that likely form the clock generation, keyboard signal debouncing, and other miscellaneous functions.

Sobax 1500 Circuit Boards

The other two boards contain primarily IC's, with very few discrete components. All of the IC's in the calculator are made by Sony, from a family of IC's that Sony developed specifically for use in their second-generation calculators. Only four different IC's make up the complement of chips in the calculator, with part numbers 501, 502, 503, and 504. The 501, 502, and 503 chips contain various combinations of NAND gates, and the 504 contains two JK flip-flops. The Sobax 1500 contains a total of 150 integrated circuit packages, with 80 501's, 26 502's, 14 503's, and 30 504's.

The three main circuit boards plug into a vertically-oriented backplane. At the top of the backplane is space for two connectors, one which connects into the keyboard assembly, and the other unused, either for manufacturing test purposes, or perhaps some kind of optional feature. Behind the backplane, across the rear of the machine lies the power supply section. The 1500 uses a standard linear power supply, with transistor regulation.

This particular machine has some logic problems that prevent it from operating properly. Sadly, it seems that many of the early IC-based Sony calculators suffer from a similar malady. I've been in touch with a number of folks who have examples of machines using these early Sony integrated circuits, and most of the machines also do not function properly. It could be that there is some kind of physical phenomenon that occurs inside the IC's, that with age that causes them to quit working. Given that the machine doesn't operate properly, I can't provide my standard 'benchmarks' on the speed of the machine, however, published performance figures show the average time for math operations. Addition and subtraction complete in 40 milliseconds (about over twice as slow as the earlier transistorized Sobax ICC-500W), multiplication in 300 milliseconds, and division in 600 milliseconds.