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Radio Shack EC-425

Date of introduction:  1974 Display technology:  LED-stick 
New price:  $79.95 Display size:  8 + 2
Size:  6.1" x 3.1" x 1.5"
 156 x 78 x 38 mm3		    
Weight:  9.2 ounces, 262 grams Serial No:  027759
Batteries:  3*AA NiCd Date of manufacture:  wk 45 year 1974
AC-Adapter:  AC9130 Origin of manufacture:  USA
Precision:  8 digits Integrated circuits:  TMS0120
Memories:      
Program steps:   Courtesy of:  Joerg Woerner

This EC-425 distributed by Radio Shack (A Tandy corporation company) could be easily identified as a restyled SR-10. The mold of the housing looks very similar to other restyled Wedge area calculators like the Montgomery Ward P200.

Dismantling this Radio Shack EC-425 manufactured in October 1974 reveals indeed the printed circuit board (PCB) of the SR-10. It makes use of the TMS0120 single-chip calculator circuit derived from the TMS1802, better known as first "calculator-on-a-chip". The remaining components found inside an early SR-10 are known from the Datamath, too. Two display-drivers each for the segments and digits of the LED-modules and a discrete power converter to generate the three different supplies inside the calculator.

The LED display vary from calculator to calculator, this one uses a Bowmar Optostic.



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

© Joerg Woerner, December 5, 2001. No reprints without written permission.