Texas Instruments SR-10 Version 2 (Rebuilt)

Date of introduction:  December 1976 Display technology:  LED modules + lens
New price:  ($149.95) Display size:  8 + 2
Size:  6.3" x 3.1" x 1.5"
 158 x 78 x 38 mm3
Weight:  9.2 ounces, 262 grams Serial No:  941644
Batteries:  3*AA NiCd Date of manufacture:  wk 50 year 1976 (Rebuilt)
AC-Adapter:  AC9200, AC9130 Origin of manufacture:  USA
Precision:  8 Integrated circuits:  TMS0120, 2*SN27915, 2*SN27423
Logic:  Chain Displays:  DIS115F (12*DISXXX)
Program steps:   Courtesy of:  Joerg Woerner
    Download manuals:   (US: 4.0M Bytes)
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The SR-10 was introduced only few month after TI's first calculator, the famous Datamath or TI-2500. Today we wouldn't call it a Scientific calculator, but it used the scientific notation on the display. Texas Instruments targeted the slide rules, guess what the abbreviation "SR" in the designation stands for.

Dismantling this unique SR-10 rebuilt in December 1976 by Texas Instruments reveals an internal construction identical with the  SR-10 Version 2 manufactured between December 1973 and Spring 1975. We assume that Texas Instruments' Repair Center was in December 1976 short of original keyboards and combined some blue keys from both the TI-150 ([C] key] and Montgomery Ward P300 [1/x], [x2], and [sqrx] keys) with the white, gray, and orange keys of the original SR-10. 

The SR-10 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 basically known from the Datamath, too.

The two plus two display-drivers SN27915 (SN75493) and SN27423 (SN75494) located in the featured SR-10 are improvements of the original SN75491/SN75492 chips introduced with the TMS1802 but allow for operation at lower voltages. The lower half of the printed circuit board (PCB) contains mainly a discrete power converter to generate the three different supplies voltages used with the calculator and the generation of the clock signal for the TMS0120 chip.

Klixon™ type keyboard looks very similar to the Datamath calculator with some additional keys placed in the upper line. Later calculators like the SR-11 changed the style of keys but the extreme wedge-style of the housing consists nearly 2 years. Last model in the wedge design was the SR-16. Don't miss to explore the huge wedge calculators SR-20 and SR-22.

horizontal rule

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© Joerg Woerner, Aptil 4, 2021. No reprints without written permission.