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Texas Instruments SR-50 (The Netherlands)

Date of introduction:  January 1975 Display technology:  LED modules + lens
New price:   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:  91xxxxxx
Batteries:  BP1 Date of manufacture:  wk 50 year 1974
AC-Adapter:  AC9200 Origin of manufacture:  The Netherlands
Precision:  13 Integrated circuits:  TMC0501, TMC0521
Memories:  1    
Program steps:   Courtesy of:  Marie Lisa Collas
Download leaflet:   Download manual:   (US: 5.6 MByte)

Fellow calculator collector Marie Lisa Collas surprised us recently with some pictures of a very unusual SR-50 missing the silver bezel around the display frame and the upper row of keys. At first glance we thought about a nice Do-It-Yourself work of a talented calculator owner but Marie fueled our doubts.

Disassembling this SR-50 manufactured in December 1974 by Texas Instruments in Almelo, The Netherlands reveals the original printed circuit boards (PCB's) centered around the TMC0501 building blocks with the Arithmetic chip and the SCOM (scanning read only memory) surrounded by some discrete logic and the display drivers.

Most important detail is the date code printed on the two integrated circuits, "7436" and "7441" translates to week 36 resp. 41 in the year 1974 - matching the December 1974 timestamp of the calculator.

The bezel of the calculator is indeed perfect and we couldn't solve the question:

Texas Instruments or Do-It-Yourself?

We even considered an early phase-out of the SR-50 in the European manufacturing site to prepare production of its successor SR-50A introduced in March 1975. But we know about an SR-50 produced in May 1975 (!) in Almelo, The Netherlands sporting the silver bezel!

Fellow collectors - if you know more about this Frankenstein calculator, please get in touch with us.

Update - May 29, 2016: Marie Lisa Collas acquired in Brazil a SR-50 manufactured for Dismac Industrial S.A. in December 1974, too. One step closer.

  

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

Joerg Woerner, November 1, 2011. No reprints without written permission.