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Tandy EC-306 Electronic Chequebook Calculator

Date of introduction:  November 1982 Display technology:  LCD
New price:  $19.95 (SRP November 1982) Display size:  8
Size:  2.8" x 6.0" x 0.30"
 71 x 154 x 8 mm3
   
Weight:  2.8 ounces, 80 grams Serial No:  
Batteries:  2*LR44 Date of manufacture:  mth 01 year 1986
AC-Adapter:   Origin of manufacture:  Hong Kong
Precision:  8  Integrated circuits:  NEC uPD1833G
Memories:  3    
Program steps:   Courtesy of:  Ken H. Meine
Download schematics:   (US: 0.6 MByte) Download manual:   (US: 2.2 MByte)

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:

Memory 1 [CHK] [DEP] [BAL] [A]
Memory 2 [PMT] [CHG] [BAL] [B]
Memory 3 [PMT] [CHG] [BAL] [C]
Total sum of Memories [GT]

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:

Indicator (--) Floating decimal with manual insertion of the decimal using the [.] key
Indicator (AM) Add mode with the decimal automatically put in the dollars and cents position (0.00)

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:

Canon Checkbook - Missing the Toggle Key for the decimal mode
Royal LCB 841 - The Art of Perfection in Japan
Royal LCB 835 - Just one Memory (uPD1831G)
Texas Instruments TI-2200 Checkwriter - Late, but not too late
Unisonic LC 262CK Check Master - Credit Card sized

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:

Canon Checkbook II - Toshiba inside
Casio CB-80 - Hitachi inside
Unisonic LC 224CK Check Master - Sharp Inside
Texas Instruments TI-2200 II Checkwriter - Toshiba + Solar cells = Winning formula

Dismantling the featured Tandy Electronic Chequebook Calculator EC-306 manufactured in January 1986 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 1A6 date code on the pictured calculator.

Inspecting the PCB of this Tandy EC-306 brought our attention to a small mark reading 2300306-02, most likely a reference to EC-306 and Revision 02 of the design (schematics and layout). We compiled a list of the PCB-Marks we discovered with similar Account Manager calculators. Please compare this EC-306 with the IMA 130CBW introduced in June 1982 and manufactured in Hong Kong, too.

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, February 8, 2020. No reprints without written permission.