Texas Instruments TI-2550 III (Version 1)

Date of introduction:  1976 Display technology:  Fluorescent
New price:  $29.95, 24.95 Display size:  8
Size:  5.8" x 3.2" x 1.3"
 147 x 81 x 32 mm3
Weight:  6 ounces, 170 grams Serial No:  019159
Batteries:  BP3 Date of manufacture:  wk 37 year 1976
AC-Adapter:  AC9130A Origin of manufacture:  USA (LTA)
Precision:   Integrated circuits:  TMS1043 (ZA0352 AP 732)
Memories:   Displays:  Itron FG95B1
Program steps:   Courtesy of:  Joerg Woerner
    Download manual:   (US: 2.8M Bytes)

The TI-2550 III replaced within few month the TI-2550 II which lacked the [+/-] key to change the sign of an entry. Unfortunately lacks the TI-2550 III the [F/2] switch of its predecessor.

The featured TI-2550 III with Date code 3776 LTA was manufactured in September 1976 by Texas Instruments in their Lubbock, TX facility. Dismantling this TI-2550 III reveals a design centered centered around a TMS1043 single-chip calculator circuit connected to a 9-digit Itron FG95B1 Vacuum Fluorescent Display (VFD) and powered by a BP3 battery pack with one AA-sized rechargeable NiCd battery. Please notice that Texas Instruments designed the calculator to accommodate the NEC LD8118L VFD, too. We refer these models as TI-2550 III (Version 2).

Main driver for these design changes were obviously manufacturing costs, comparing the printed circuit boards (PCBs) of the original TI-2550 II and its successor TI-2550 III calculator reveals significant differences:

Resistors to bias the VF Display integrated into TMS1043
Power-up Clear integrated into TMS1043
Capacitor for Clock Oscillator integrated into TMS1043
   (Note: We observed on some TI-2550 III calculators a small 33pF capacitor soldered to the TMS1043, probably to calibrate its operating speed)

In addition with removing one of the two AA-sized rechargeable NiCd batteries found in the original BP2 battery pack the cost reductions added up and similar electronics was used even with the TI-1265.

The TMS1043 is a member of the TMS1040 Product Family based on the TMS1070 "computer-on-a-chip" introduced in 1974 with the original TMS1000. While the TMS1070 can directly interface with low-voltage VFDs up to 35 Volts does it still need external resistors and a zener diode to bias the anodes and grids of the display with respect to the filament. The TMS1040 added an extra VPP pin to connect a negative 30 Volts bias voltage for its modified output drivers. With the TMS1070 featuring 11 R Outputs for the Digits, 8 O Outputs for the Segments and 4 K Inputs for the Keyboard, reduced the TMS1040 the number of R Outputs to 9, consequently are all known TMS1040 calculator designs using a 9-digit VF Display.

Ever wondered why we disassembled this TI-2550 III completely and desoldered its components? Learn more about Characterization of Single-Chip Calculator Circuits with the DCM-50A Platform.

A similar calculator chip was used with the innovative Canon MD-8 sporting a multi-line display.

The other changes were minor, the layout of the keyboard was better organized.

This beautiful calculator was discontinued in 1977 and marks in most markets the end of the TI-2550 Product Family started in January 1974. In some European countries the rare TI-2550-IV extended its heritage for another year.

If you add the [pi] key to this calculator you get the Canon Palmtronic F-31 or Toshiba BC-8112SL. A more compact design was introduced with the Canon Palmtronic LD-8Ms.

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If you have additions to the above article please email:

Joerg Woerner, December 5, 2001. No reprints without written permission.