Texas Instruments SR-51A Version 1

Date of introduction:  June 1975 Display technology:  LED-stick
New price:  $224.95 Display size:  10 + 2
Size:  5.8" x 3.2" x 1.3"
 147 x 81 x 32 mm3
Weight:  8.5 ounces, 240 grams Serial No:  84801
Batteries:  BP1A Date of manufacture:  wk 40 year 1975
AC-Adapter:  AC9130, AC9130A Origin of manufacture:  USA
Precision:  13 Integrated circuits:  TMC0501, TMC0522, TMC0523
Memories:  3    
Program steps:   Courtesy of:  Joerg Woerner

The SR-51A was introduced shortly after the SR-51 to reduce manufacturing costs. You won't notice too much differences to the SR-51, the keyboard layout kept each key on it's place, only the colors changed. You have to open the calculator to understand the differences, the rigid inner keyboard frame of the SR-51 was removed, the LED modules replaced with a LED-stick and bubble-lens magnifier. The appearance of the SR-51A is similar to the later SR-52 and SR-56 calculators. 

Mid of 1975 Texas Instruments line of scientific calculators consists of:

SR-16:  Lowest end, still in the huge SR-10 housing
SR-40:  Lower end, never introduced to market
SR-50A: Volume model, all scientific functions
SR-51A: High end, includes statistical functions

Lifetime of the SR-51A was longer than the unfortunate SR-51, next calculator in that line was the SR-51-II.

SR-51A_0_PCB.jpg (76291 Byte)The hardware of the SR-51A is based on the TMC0500 Building Blocks for Scientific and Programmable Calculators and uses the TMC0501 Arithmetic Chip with an accuracy of 13 digits and two TMC0522/TMC0523 SCOM (Scanning and Read Only Memory) Chips containing 1k*13 Bits instruction memory, each and 16*16 digits constants each. The second SCOM Chip is mounted in a piggy-back manner on top of the first SCOM Chip to accommodate the SR-50A printed circuit board (PCB).

SR-51A_1_PCB.jpg (86667 Byte)In the last production year the SR-51A uses identical hardware to the SR-56. One of the necessary changes were the new SCOM Chips TMC0532/TMC0533 instead the former TMC0522/TMC0523.

The SR-51A is featured in the Texas Instruments Deutschland GmbH leaflets ER-1975 and ER-1976 dated 1975 resp. 1976.

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If you have additions to the above article please email:

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