MBO Expert (7C-903)

This MBO Expert was one of the last "four-banger" calculators in decent manufacturing quality during the heights of the Calculator Wars in 1975 before products like the Far East Generic Design I took over.

MBO International Electronic GmbH, Jena was founded 1973 and started with the MBO Junior the production of the first portable calculator in Germany. Later MBO actually placed their name stickers on Far-East OEM products.

Dismantling this MBO Expert calculator manufactured in October 1975 in Asia reveals a clean design based on a single-sided printed circuit board (PCB) for the main electronics and a double-sided PCB for the keyboard and powered by a disposable 9 Volts battery.

The main PCB is centered around a TMS0833 single-chip calculator circuit manufactured by Texas Instruments and a Bowmar BD 5026 Digit Driver chip. The few remaining components on the PCB are mainly used to generate the clock signal for the internal timing of the TMS0833 and an additional transistor for the 8^th digit of the LED display.

The TMS0833 is a member of the TMS0800 family, introduced in 1973/1974 and following the original TMS0100 "Calculator-on-a-chip" and adopting the low-voltage PMOS process developed for the TMS0950 used with the TI-1200.

With the DCM-50A Platform developed to Characterize and Reverse-engineer Single-chip Calculator Circuits we could proof that the TMS0833 uses the same program code as the TMS0803 known from the TI-1500.

The unusual BD 5026 display driver located with this MBO Expert manufactured in October 1975 is a relict of Bowmar's unsuccessful venture as manufacturer of Integrated Circuits before filing in 1976 for bankruptcy.

The display module of the MBO Expert uses nine small LED chips bonded on a substrate with an additional magnifying lens to enlarge the digits.

If you have additions to the above article please email: joerg@datamath.org.

© Joerg Woerner, September 6, 2022. No reprints without written permission.