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Sharp Compet 363 and Facit Model 1135J Desk Calculators

CS-363 external view Sharp Model CS-363, S/N 11001705
Functions: ASMD, K, 3 memories
Technology: MOS-LSI (Rockwell, 6 chips)
Display: 16 digits, Nixie tubes
Dimensions: 295W x 335D x 100H, weight: 3.9kg
Manufactured: Sharp, Japan, March 1971.

Facit 1135J External View (8kb) Facit Model 1135J, S/N 3500315
Functions: ASMD, K, square root, 3 memories
Technology: MOS-LSI (Rockwell, 7 chips)
Display: 16 digit, Nixie tubes
Dimensions: 300W x 330D x 105H, weight 4.24kg
Manufactured: Sharp, Japan, October 1971.



The Facit organisation built an extensive range of mechanical calculators at Atvidaberg in Sweden from the early 1920s to the 1970s. In 1966 they introduced the first of a range of electronic calculators which were sourced from Sharp in Japan. The design and function of the Facit-branded machines is generally similar to the Sharp "Compet" machines of the time.

The Facit Model 1135J from 1971 is an enhanced version of the Sharp Compet CS-363 calculator. The general arrangement of the two machines is identical, but the Facit has a different external casing, a different memory arrangement, and some additional chips on the processor board to provide square root and automatic accumulation functions. This page illustrates the Facit version, and notes the differences where appropriate.



Internal View (28kb) Internal view

The main circuit board, display board, and power supply are mounted in three metal carriers in the lower section of the case. The main board is at the bottom, with the display and power supply above. There is a metal shield plate attached to the base, but it is not electrically connected.

CS-363 main board (34kb) Sharp CS-363 main board

The processor circuitry is contained on one double-sided phenolic board measuring 255 x 185mm. The board is mounted in a metal frame, which attaches to the base of the machine with two screws. There are two 2x22-way edge connectors near the centre for the keyboard (left, mounted vertically) and the display board (right, mounted horizontally). The 2x11-way connector at the top left is accessible externally after removing a screw-on cover panel at the rear of the case. There is no label or other indication of the purpose of this connector.

The processor uses a set of six Rockwell MOS-LSI chips in 42-pin ceramic flat-packs. The part numbers are 10061 to 10066, with date codes from November 1970 to February 1971. The board itself is dated March 1971. The circuitry operates from a single -25V DC regulated supply which is connected via the display board.

Main board (38kb) Facit 1135J main board

The Facit main board is essentially the same, but with an additional Rockwell 10328 LSI chip and 6 NEC chips in DIL packages to provide the square root and memory accumulation functions. The chip date codes range from March to October of 1971. The board has SHARP etched into the copper pattern in the upper right, and is stamped with a date code "46.8.26" (26 August 1971) in the traditional Japanese format.

Display board (25kb) Display board

The display board measures 255 x 100mm, and is dated August 1971. It is supported in a metal frame which mounts above the forward section of the processor board, and is secured by the same two screws.

The numerical display uses sixteen multiplexed Nixie tubes with discrete-transistor drivers. The tubes are 12mm diameter with numerals 12mm high, and are mounted on 14mm centres. The tubes have a comma symbol at the lower left (which is used as a thousands separator), and a decimal point at the lower right.

A special tube at the right-hand side has indicators for the three memories, a minus sign, and a large E for error. The 3-wire flying lead at the right is the incoming connection from the power supply.

Power supply (23kb) Power supply

The power supply is a self-contained module which mounts above the main board at the rear of the case. The Facit (illustrated) has an IEC input socket and provision for a mains voltage selector. The Sharp has a selector for 100 to 240V, but uses a custom input socket (similar to the IEC but with round pins). The power input is rated at 16W.

The power supply produces a regulated -25V DC supply for the logic circuits, and +190V DC for the Nixie display tubes. It has a plug and socket connection to the display board via the three pins at the upper left.

Keyboard assembly (30kb) Keyboard assembly

The keyboard assembly is mounted in the upper section of the case, and is attached to the processor board via a card edge connector on a flying lead.

The keyboard is built in four separate sections, which are mounted on a substantial metal plate. The mechanism uses glass reed switches, operated by moving magnets on the ends of the keystems. The main numeric keypad has a mechanical interlock to prevent more than one key being pressed at a time. There is an inaccessible 24-pin DIL IC (Mitsubishi M54510, presumably some form of encoder) mounted on the under side of the largest circuit board.



Keyboard (28kb)

The control panel of the Facit 1135J is dominated by the three sets of memory control keys on the right-hand side. The two slider switches above the memory keys control various automatic-accumulation functions. Three indicators at the right of the display show when the memories are active.

The Sharp machine does not have the automatic accumulation functions, and only has two sets of memory keys. The second set connects to either MII or MIII, according to the setting of an adjacent slider switch.

On the left of the keyboard are two pairs of slider switches which set the decimal places (0 to 7 or floating) and roundoff for the display and the memories separately. There is a latching K (for constant) key, and RV to swap the display register and the internal buffer. Clear and Clear Entry operate as expected. Both machines have the same function keys, but with minor differences in the layout.

The four function keys in the centre operate as expected, with Plus and Minus working in adding-machine fashion. The Multiply and Divide keys have lamps behind the symbols to show when an operation is pending (including when K is active).

The display is right-aligned according to the setting of the decimals switch, with leading zeros suppressed. Trailing zeros are preserved in floating mode - 2.0 x 2.0 produces 4.00, not just 4. The comma symbols provide active thousands separators in the area to the left of the decimal point.

Although it is not obvious from the keyboard, the Facit-branded machine provides both square and square root functions by using the Mult and Div keys without a second argument. For example, 2 Mult Equals produces the square (4), while 2 Div Equals produces the square root (1.414).

Original text and images Copyright © John Wolff 2007-11.
Use at own risk; beware of errors; suggestions for improvement welcome.
Last Updated: 30 November 2011

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