Radio Shack EC-306 Electronic Checkbook Calculator

National Semiconductor introduced already in 1978 with the NS103 Data Checker an electronic record keeper with three continuous memories to track bank and charge account balances with dedicated keys:

While the NS103 Data Checker was based on proprietary technology, introduced NEC of Japan with the uPD1833G in 1980 a single-chip calculator circuit that created the blueprint for checkbook-sized Account Manager calculators and thereupon the market got swamped with products based on this design. The uPD1833G simplified the use of the memories by removing the redundant [A], [B], and [C] keys and replaced the inconvenient three-way power-switch of the NS103 Data Checker with two dedicated [ON] and [OFF] keys and a [DS] key to toggle between two entry modes:

Even the successor of the NS103, known as NS103A, switched its internals to the uPD1833G but we feature some more Account Manager calculators in the Datamath Calculator Museum based on this technology:

NEC of Japan lost some market share with their design for Account Manager calculators in the Eighties, when competitors like Hitachi and Sharp introduced similar chips and finally lost the business completely to Toshiba's "Solar Cells" compatible design. Find more Account Manager calculators in the Datamath Calculator Museum:

Dismantling the featured Radio Shack Electronic Checkbook Calculator EC-306 manufactured in January 1985 in Hong Kong reveals a clean design centered around a NEC uPD1833G single-chip calculator circuit soldered on a single-sided printed circuit board (PCB) and powered by two LR44 batteries. Learn how to decipher the 1A5 date code on the pictured calculator.

Radio Shack, acquired by Tandy Corporation in 1963, entered the market of Checkbook Calculators in November with this EC-306. It features Account Manager functionality with three permanent (till you remove the batteries) Memories and started a very successful product line. We discovered as of now seven (w/o counting Tandy versions) different family members:

Printed Circuit Board Marks

Inspecting the PCB of the EC-306 brought our attention to a small mark reading 2310306-01, most likely a reference to EC-306 and Revision 01 of the design (schematics and layout). Please compare this EC-306 with the IMA 130CBW introduced already in June 1982 and manufactured in Hong Kong, too.

We noticed during our research of Account Manager or Checkbook Calculators similar marks on the PCBs of other products and compiled a first overview:

It looks like most of these calculators are based on a generic OEM design and just modified for the various brands. Calculators from Canon and Casio seem to be an exception, they exhibit a completely different internal design and feature PCB-Marks with their own brands.

Learn more about single-chip calculator circuits used in Account Manager Calculators.

Don't miss the Corvus CheckMaster introduced by Mostek already in 1975. This rare product retains the balance of your memory even when shut off but uses power-hungry electronics.

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

© Joerg Woerner, January 15, 2020. No reprints without written permission.