Texas Instruments TI-1750 (2nd design)

Date of introduction:  December 1977 Display technology:  LCD (yellow)
New price:  $19.35 Display size:  8
Size:  4.5" x 2.7" x 0.35"
 115 x 68 x 9 mm3
Weight:  2.3 ounces, 65 grams Serial No:  119653
Batteries:  2*LR44 Date of manufacture:  mth 12 year 1977
AC-Adapter:   Origin of manufacture:  Japan
Precision:  8 Integrated circuits:  Toshiba T3603
Memories:  1    
Program steps:   Courtesy of:  Stefan Klaes
    Download manual:   (US: 0.8M Bytes)

With the TI-1750 Texas Instruments entered in 1977 the market of LCD-calculators. It is very obvious that it wasn’t manufactured by Texas Instruments. Even the internal construction looks different to typical Texas Instruments calculators like the later TI-1030. Which company is really behind the TI-1750? Comparing the TI-1750 with the Toshiba LC-844 gives the impression that is is a Toshiba design like their OEM calculator Radio Shack EC-264. Dismantling some TI-1750 from the Datamath Museum collection gives not only one but five different TI-1750 models:

Version Date of 
Serial No. Battery IC
1st mth 07 year 1977 213387 3*LR44 Toshiba T3532
2nd mth 12 year 1977 119653 2*LR44 Toshiba T3603
3rd (early) mth 10 year 1978 888828 2*LR44 Toshiba T3709
3rd (late) mth 09 year 1979 711171 2*LR44 Toshiba T3709
4th mth 10 year 1978 014178 2*LR44 Sharp LI3023M

• The 1st design use a very complex approach compared to other LCD-calculators 
    of that era like the Sharp EL-8020. A small detail is the connection between the 
    LCD-contacts and the traces of the PCB. Instead the usual zebra-stripe 
    (an arrangement of conductive and isolation rubber pieces) discrete coil springs 
    are used.
• The 2nd design still uses discrete coil springs to connect the LCD-contacts with 
    the PCB traces but uses a smaller calculator chip
in a 43-pin QFP (Quad Flat Pack)

• The 3rd design uses a much simpler approach and shows a huge cost reduction. 
    It resembles the typical style of LCD-calculators sold in 1978. A funny detail is 
    the battery holder accommodating two coin cells and one plastic dummy battery!
• Later models of the 3rd design corrected this flaw and modified the battery holder 
    down for two cells.
The 4th design looks nearly identical but uses different parts. The internal plastic 
    frame of the housing and the printed circuit board were changed to use a Sharp 
    calculator brain instead the Toshiba chips found in the other versions. 
    From outside you notice the different position of the LC-display and the shape 
    of the display frame.

The internal construction is totally different. The 1st design uses a huge 42-pin DIL (Dual In Line) plastic housing instead this 43-pin QFP (Quad Flat Pack) housing. TI-1750_VX_PCB.jpg (37970 Byte)
The connection between the LCD and the PCB is done with small springs instead the later conductive rubber stripe. TI-1750_VX_LCD.jpg (11033 Byte)
The 2nd design of the TI-1750 uses a battery holder to accommodate 3 coin batteries. One of them is blocked with a dummy battery. TI-1750_VX_BAT.jpg (24279 Byte)

There are different rumors which companies designed and manufactured the TI-1750, usually you get Toshiba and Sharp. Comparing the 4 versions with similar calculators manufactured by Sharp we could reject this speculation. On the other hand we can’t believe that Toshiba used a calculator chip from competitor Sharp.

Searching all parts for a hint to possible manufacturers gives you the Sansyu logo.

Sansyu Precision Co., Ltd. (Hieda, Japan) was founded in 1976 and specialized in precision plastic and metal processing. Main products are Injection Molding, Metal Stamping and Assembly. The construction of the TI-1750 makes heavily use of both injection molded plastic parts (display frame, internal frame, on-switch, keys) and sheet metal (housing top and bottom). Fits perfectly ! Let us assume that Toshiba designed the calculator and Sansyu Precision was responsible for both the tooling and manufacturing. It could be possible that the 1st design was changed to both Toshiba and Sharp calculator chips to get a second source in the case of component shortage.

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© Joerg Woerner, December 14, 2002. No reprints without written permission.