Texas Instruments SR-51-II

Date of introduction:  1976 Display technology:  LED-stick
New price:  $79.95, 39.95 Display size:  10 (8 + 2)
Size:  5.8" x 3.1" x 1.4"
 148 x 78 x 36 mm3
Weight:  7.0 ounces, 198 grams Serial No:  2016564
Batteries:  BP6 Date of manufacture:  wk 44 year 1977
AC-Adapter:  AC9131 Origin of manufacture:  USA
Precision:  12 Integrated circuits:  TMC0501, TMC0581
Memories:  3    
Program steps:   Courtesy of:  Joerg Woerner
    Download manual: (US: 10.9 MBytes)

The advanced calculator is a very interesting hybrid between the well known SR-51A and the later TI-55

To understand the position of the calculator you must remember that TI introduced the SR-40 with its one-chip design in 1976 but the advanced one-chip TI-55 later in 1977. The SR-51-II used the housing of them with the very complex electronics of the earlier SR-51A. If you open the housing you'll find a very interesting constructions with some stacked printed circuit boards (PCB) behind the LED display.  Conclusion: Don't underestimate this machine!

If you dismantle a SR-51-II you'll notice a different construction compared to the TI-30. The SR-51-II carries "real" electronics, not just one integrated circuit. SR-51-II_PCB1.jpg (97529 Byte)
Stefan Klaes - a fellow collector of TI-calculators living in Germany - explored the whole story of the SR-51-II. Find his wonderful pictures in the Datamath Museum. SR-51-II_PCB2.jpg (114822 Byte)
In a first step he removed the power-supply circuit from the mainboard. SR-51-II_PCB3.jpg (88043 Byte)
The power-supply is the usual switching circuit known from the SR-50 series. SR-51-II_PCB4.jpg (70287 Byte)
The SR-51-II uses indeed the circuit of the SR-51A! 
Thanks, Stefan.
SR-51-II_PCB5.jpg (90622 Byte)

Another interesting detail is the battery pack, the BP6 model was used only in the SR-51-II and early TI-57 models.

According to Texas Instruments the SR-51 II was manufactured till 1979.

Find here an excerpt from the TI Learning Center leaflet CB-272 dated 1976:

SR-51-II. Advanced professional electronic calculator.

This powerful, full-functioning calculator is ideal for the advanced high school student to grow with into college and career. It offers solutions to simple arithmetic as well as trigonometric, logarithmic, and hyperbolic functions. It performs all the classical slide-rule functions and more: roots and powers, factorials, reciprocals, percent and percent-change, linear regression and trend-line analysis. Students can use the SR-51-II to help them with complex statistical problems as well: mean, variance, standard deviation and correlation among with seven unit conversions by direct key. It has three addressable memories with direct memory arithmetic and memory/display exchange.

TIs AOS algebraic operating system allows complex mathematic expressions to be entered in the same order that they are written. Up to nine levels of parentheses are available to ensure proper and accurate interpretation of expressions. And, it handles up to five pending operations.

A fixed decimal option provides results displayed to as many as eight decimal places at directions of user. And, the SR-51-II can state numbers in scientific or engineering notation.

Calculating Better Decisions, a challenging and informative book, illustrates how the advanced, professional SR-51-II calculator can be a powerful decision-making tool in school, business and everyday life

Texas Instruments, 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.