Radio Shack EC-306 Electronic Checkbook 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 1985
AC-Adapter:   Origin of manufacture:  Hong Kong
Precision:  8  Integrated circuits:  NEC uPD1833G
Memories:  3    
Program steps:   Courtesy of:  Joerg Woerner
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 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:

• 1982: Radio Shack EC-306 / 65-696, 3 Memories
• 1982: Tandy EC-306 / 65-696, 3 Memories
• 1987: Radio Shack EC-308 / 65-996, 3 Memories
• 1987: Radio Shack EC-430 / 65-570, 3 Memories, Taiwan
• 1988: Radio Shack EC-430 / 65-570A, 3 Memories, Thailand
• 1996: Radio Shack EC-455 / 65-569, 1 Memory, TAX
• 2000: Radio Shack 65-504, 3 Memories, TAX, violet CC keys
• 2002: Radio Shack 65-504A, 3 Memories, TAX, blue CC keys

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:

PCB Mark


Calculator Chip



Date Code

Country of Manufacture

306 01 NEC uPD1833G 3 Memories Radio Shack EC-306 1A5
Jan. 1985
Hong Kong
306 02 NEC uPD1833G 3 Memories Tandy EC-306 1A6
Jan. 1986
Hong Kong
307 10 Sharp LI3330MT 1 Memory, TAX Royal CBC 70
Unisonic LC 226CK
Nov. 1988
Aug. 1991
308 15 Toshiba T7752S 3 Memories, Password TI-2200 II C-0695
Jun. 1995
308 16 Toshiba T7752S 3 Memories, Password Royal CBC 80NT
Unisonic LC 266CK
308 17 Toshiba T7752S 3 Memories, Password Royal CBC 80 1988 Thailand
308 18 Toshiba T7752S 3 Memories, Password Royal CBC 80
Royal/Olivetti CBC 80
Olivetti DII
Royal CBC 95
308-II 02 Toshiba T7752S 3 Memories, Password TI-2200 II C-0387
Mar. 1987
309T 10 NEC uPD1833G 3 Memories TI-2200
TI-2200 II (EU)
Dec. 1982
Oct. 1984
310 2 NEC uPD1832G 1 Memory Unisonic LC 224CKE Sep. 1983 Taiwan
310S 10 Sharp LI3329MT 1 Memory Unisonic LC 224CK Sep. 1983 Taiwan
0158-0810 R1 Sharp LI3154 1 Memory, TAX Radio Shack EC-455 1998 Malaysia
103   NEC uPD1833G 3 Memories National Semiconductor NS103 1978 Taiwan
103 B 1 NEC uPD1833G 3 Memories National Semiconductor NS103A
NSC Novus Electronics NS103A
1981 Taiwan
103 C NEC uPD1831G 1 Memory NSC Novus Electronics NS101A 1981 Taiwan
103 C-2 NEC uPD1831G 1 Memory NSC Novus Electronics NS101A 1982 Taiwan
103 C-12 NEC uPD1831G 1 Memory Hoffmann-La Roche FITNESS 3 1983 Taiwan
107   NEC uPD183XG 2+1 Memories National Semiconductor NS107 1980 Taiwan
107  2 NEC uPD1833G 3 Memories Unisonic LC262 CK 1983 Taiwan
151 1834G
  NEC uPD1843G 1+1 Memories Aurora AC-22 PASSPORT 1985 Taiwan
203 3 Mitsubishi  M58490P 3 Memories Unisonic LC 262 1979 Taiwan
830 10 NEC uPD1832G 1 Memory Royal LCB 830 May 1983 Taiwan
830A 10 NEC uPD1831G 1 Memory Royal LCB 835 Jul. 1983 Taiwan
841   NEC uPD1833G 3 Memories Royal LCB 841 Aug. 1980 Japan
3 NEC uPD1833G 3 Memories Aurora CB-900 May 1983 Taiwan
CB 10 Toshiba T7752S 3 Memories Canon Checkbook III tbd Thailand
I24-N 10 NEC uPD1832G 1 Memory APF 3552CK Sep. 1982 Taiwan
I24-S 10 Sharp LI3329MT 1 Memory Enterprex MC-2717 Sep. 1984 Taiwan
I074F 02B unknown 1 Memory Technico LC 741CK 1984 Taiwan
KC-129AP AA04 unknown 1+100 Memories Datexx DC-80 tbd China

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