Radio Shack 65-504A

Date of introduction:  October 2002 Display technology:  LCD
New price:  $19.99 (SRP October 2002) Display size:  8
Size:  3.0" x 6.2" x 0.30"
 75 x 157 x 8 mm3
Weight:  3.2 ounces, 91 grams Serial No:  
Batteries:  2*LR43 Date of manufacture:  mth 10 year 2003
AC-Adapter:   Origin of manufacture:  China
Precision:  8  Integrated circuits:  T66L16
Memories:  3+1+60    
Program steps:   Courtesy of:  Ken H. Meine
    Download manual:   (US: 3.5 MByte)

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

Dismantling the featured Radio Shack 65-504 Checkbook Calculator manufactured in October 2003 in China reveals a clean design centered around around a T66L16 single-chip calculator circuit mounted in Chip-On-Board (COB) technology directly on the printed circuit board and hiding under a small epoxy blob. The electronics is powered by two small LR43 batteries. Learn how to decipher the 10A03 date code on the pictured calculator.

Inspecting the PCB of this 65-504A manufactured in 2003 brought our attention to a small mark reading DB-413 REV:7, a reference to Datexx DB-413, and Revision 7 of the design (schematics and layout).

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, February 26, 2020. No reprints without written permission.