Radio Shack EC-300

Date of introduction:  1974 Display technology:  LED-modules + lens
New price:  $114.95 Display size:  8
Size:  5.8" x 3.5" x 1.9"
 148 x 88 x 48 mm3
Weight:  6.7 ounces, 191 grams Serial No:  300-17186
Batteries:  4*AA Date of manufacture:  wk 20 year 1974
AC-Adapter:   Origin of manufacture:  USA
Precision:  8 Integrated circuits:  WD LC1552B
Memories:  1    
Program steps:   Courtesy of:  Mike Sebastian

This EC-300 does not look like a Texas Instruments product and made a great design evolution compared to the earlier EC-200

EC-300CHIP.jpg (16102 Byte)If we dismantle this calculator, one question will immediately arise: Which company manufactured this EC-300? Searching the single-chip calculator circuit reveals a great surprise: The huge IC carries the logo of Western Digital and is one step ahead the TI chips of that era:

The TI-2550 with similar complexity (%-key and 4-key memory) was introduced later. Maybe TI had a delay in the development of the TMS0601, the direct counterpart of the Western Digital LC1552 used in the EC-300 and the Montgomery Ward P8P. Interesting note: Bowmar used with the MX-55 the same chip for a calculator without memory. The keyboard of the calculator is a mixture of the TI-1500 keys and the grid of the Datamath.

In 2001 we were indeed not sure who manufactured the EC-300. The owner of this wonderful EC-300, Mike Sebastian noticed a small indicator in the manual of his calculator: 

We know this address! Just compare it with the well known Texas Instruments consumer service facilities of the year 1974 and found on a SR-10:

Texas Instruments Service Facility
P.O. Box 5012 M/S 10
Dallas, Texas 75222 

EC-300_1.jpg (11735 Byte)Nevertheless, this is the Service Center - maybe TI offered just the repair service for Radio Shack. In 2003 we finally found the answer when we explored the EC-1000, a desktop calculator matching the design line of this EC-300. This calculator looks and feels like a TI product but carries no TI logo inside. The secret of both calculators is a magic number on the printed circuit board (PCB): 13-04-709-479 - read more here.

The battery compartment of the EC-300 sports a small sliding switch to select between "RECHARGABLE NI-CD BATTERIES" and "ALL OTHER BATTERIES". This switch prevents the AC-Adapter from providing a charge to the batteries if the switch is set to "aALL OTHER BATTERIES".

Datamath™ is a trademark of Texas Instruments.

Known serial numbers:

A2 300-02184, A2 300-17186, A2 300-20385


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