Date of introduction:  1983 Display technology:  LCD
New price:  $10.99 (SRP Aug. 1983) Display size:  8
Size:  4.0" x 2.4" x 0.25"
 101 x 61 x 6 mm3
Weight:  1.5 ounces, 41 grams Serial No:  
Batteries:  n.a. Date of manufacture:  mth 07 year 1983
AC-Adapter:   Origin of manufacture:  Taiwan
Precision:  8  Integrated circuits:  
Memories:  1    
Program steps:   Courtesy of:  Joerg Woerner

Does this LC 685S calculator distributed in 1983 and in the United States through IMA (International Merchandising Associates) look familiar to you? Inventa Electronics Corporation of Taipei, Taiwan started already in 1975 manufacturing and marketing calculators under the Technico brand. Inventa Electronics Co. is today known as Inventec Corporation, one of the World's largest manufacturers of mobile devices and computers. We discovered the SL-674CK and its numerous offspring like this IMA LC 685S or the KMC 8000, Levi SL1673, MBO Solar SP20, Migros SL 671 and Olympia SL674CK on our quest to learn more about the roots of the TI-1755 SLR introduced in 1983. While we found proof that TI-1754, TI-1755, TI-1756 and TI-1757 II are actually rebranded Inventa calculators, doesn't fit the TI-1755 SLR into the line. We decided for a thorough tear-down of the Technico SL-674CK, Olympia SL674CK (basically identical to the Technico SL-674CK but from a later manufacturing run) and the TI-1755 SLR to learn more about their relationship.

Dismantling the featured LC 685S manufactured in July 1983 by Inventa Electronics Corporation in Taiwan reveals a clean design centered around an unknown single-chip calculator circuit soldered on a double-sided printed circuit board (PCB) with just a few additional discrete components and powered by five rather large solar cells.

While this IMA LC 685S and the Technico SL-674CK look at first glance identical, could we identify three main differences based on the usage of most likely different single-chip calculator circuits and LC-Displays:

SL-674CK [AC] and [CE/C] keys, display indicators left-hand side, higher display position
LC 685S   [AC] and [ON/C] keys, display indicators right-hand side, lower display position

We assume based on these subtle differences that the IMA LC 685S makes use of a Sharp chip and the original design either a calculator brain manufactured by Toshiba or NEC.

Inspecting the PCB of the IMA LC 685S calculator brought our attention to a small mark reading I674C-05G while we located on the original Technico SL-674CK a mark reading SL6745 and the Olympia SL674CK from a later production run reads I6745A-02B.

We started compiling a list of the PCB-Marks on calculators manufactured by OEMs for Texas Instruments.

If you have additions to the above article please email:

Joerg Woerner, May 7, 2020. No reprints without written permission.