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Burroughs C5155 Desk Calculator

Burroughs C5155 Burroughs C5000 Series, Model C5155, S/N C-164938-024
Functions: ASMD, constant
Technology: MOS-LSI (AMI, 3 chips)
Display: 10 digits, 7-segment neon (Panaplex II)
Dimensions: 200W x 285D x 100H
Weight: 2.33kg
Manufactured: S.A.Burroughs, France, 1973

The Burroughs C5155 is a basic four-function desk calculator from 1973, built with MOS-LSI technology.

This page gives a very brief description of its internal arrangements.

C5155 internal view C5155 Internal View

The single circuit board of the C5155 is supported between two metal brackets at the front and rear of the base. The rear bracket carries the mains connector, power switch and fuse, an earth terminal block, and the power transformer.

The front bracket carries the keyboard assembly, which is made up from 16 individual key switches, with provision for another four on the right-hand side. A grid of thin plastic strips is installed between the keys for reasons unknown. The panel to the left of the keys carries two slider switches for decimal place selection and the "Constant" function. The keyboard assembly is dated 24 July 1973.

The calculator uses an 11-digit "Panaplex II" gas-discharge display, made by Burroughs themselves. Ten digits are used for the numeric display, and the eleventh (rightmost) for sign and error indication.

C5155 circuit board C5155 Circuit Board

All of the circuitry of the C5155 is contained on a double-sided board measuring 190 x 215mm. The date 17 Jan 1973 is etched into the copper pattern on both sides. There are plug-in connectors for the power transformer at the rear, and for the keyboard and slider switches at the front. There are no other off-board connections.

Two separate windings on the power transformer produce +18 and -12V from the two TO-3 three-terminal positive regulators (7815 and 7818). A third winding provides +180V for the display.

The processor uses three AMI chips in 40-pin ceramic packages. The part numbers are 1236-0574, 1236-0582, and 1239-8756, with date codes in November 1973. Note that pin 12 of the left-hand chip has been lifted from the socket. The discrete-transistor clock generator at the lower right produces a two-phase clock at 40 kHz.

The anodes of the multiplexed display are driven by the discrete transistors to the rear of the Panaplex socket, while the cathodes are driven by a Dionics D1289N chip in an 18-pin plastic pack.

The keyboard connects to the edge connector at the bottom front of the board, and the switch panel to the pin connector at the left.

The operation of the machine is entirely conventional, with no surprises.

Original text and images Copyright © John Wolff 2005-09.
Last Updated: 23 July 2009

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