Technico SL-674CK

Date of introduction:  1982 Display technology:  LCD
New price:   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:  year 1982
AC-Adapter:   Origin of manufacture:  Taiwan
Precision:  8  Integrated circuits:  
Memories:  1    
Program steps:   Courtesy of:  Joerg Woerner

Does this Technico SL-674CK calculator 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 IMA LC 685S, 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 SL-674CK manufactured in 1982 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.

Inspecting the PCB of the Technico SL-674CK calculator brought our attention to a small mark reading SL6745, we expected a PCB-Mark beginning with an IO like the IO800-02D of a Technico F-800, IO074D-05C of a LC-74CK or IO74F-02E of a LC 741CK, too. Please notice that the Olympia SL674CK from a later production run reads I6745A-02B and the IMA LC 685S reads I674C-05G.

IO800 obviously refers to Technico F-800, while other calculators manufactured by Inventec Corporation like the TI-1775 sport a PCB-Mark like IOTI1775-21A. We assume to decipher Inventa / Invetec PCB-Marks as follows:

IXXX, IOXXX: Original Inventa / Inventec design - brand labeled for Texas Instruments and other companies
ITTIXXX, IOTIXXX or IOBAXXX: Inventec design exclusively for Texas Instruments

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

Tear-down of Technico SL-674CK, Olympia SL674CK and Texas Instruments TI-1755 SLR

At first glance the TI-1755 SLR might look similar to the SL-674CK but we immediately noticed a complete different layout of their keyboards and a different font used for the individual keys. While the SL-674CK and TI-1754...TI-1757 II sport a constant pitch between the keys both horizontally and vertically, are the keys of the TI-1755 SLR grouped in a logical way and reminding us of the TI-1100 introduced in 1983, too. The unique "Inventa" font was replaced with a rather generic font matching other TI calculators from the Eighties. Don't miss the Technico F-1 and its offspring TI-1786 switching fonts, too.

The backside of the three calculators shows some similarities like the position of the screws and the little bumps for the integrated circuits but a completely different shape. Please notice the rounded corners and four little stands of the TI-1755 SLR compared with the Technico SL-674CK.

Removing the two screws, each from the backsides of the calculators and inspecting their printed circuit boards (PCBs) confirms our assumption: Not twins but definitively very close relatives. It is obvious that the single-chip calculator circuit of the TI-1755 SLR is much smaller than the one of the Technico SL-674CK but matches the one of the later Olympia SL674CK, suggesting that it is a Sharp design versus Toshiba or NEC. This assumption is supported by the different layout of the LC-Display, the Indicators (Memory and Sign) of the TI-1755 SLR are positioned to the right side of the numerals, we observed this already with the Enterprex MC-2717 and APF Electronics 3552CK twins. The PCB of the TI-1755 SLR centered between a first generation Technico SL-674CK and second generation Olympia SL674CK seems to be almost identical to the latter one:

Very similar geometry and layout of the PCB (Position of main components)
Identical mounting of PCB to housing
Identical design for testing during manufacturing)
Almost identical LC-Display and connection to PCB
Identical solar cells and connection to PCB
Very similar design of the molded housing parts

We consider the TI-1755 SLR as an important milestone in the coopeartion between Texas Instruments and Inventa / Inventec - while many TI calculators from 1982 were just design variations of existing OEM calculators, introduced this TI-1755 SLR some "TI-ness" to the product line and most designs thereafter followed this spirit.

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Joerg Woerner, April 16, 2020. No reprints without written permission.