Texas Instruments Fixed Income Securities SIA (Pre-series)

This Fixed Income Securities (FIS) calculator introduced by Texas Instruments in May 1989 was purchased by auction in May 2008. Usually we don't like scratches or even carvings on calculators but this one sports a promising "PROTO 10" signature on its backside. The calculator itself looks identical to any later Fixed Income Securities models and working through the 10 worksheets revealed no differences, either.

In a next step we disassembled the calculator and the printed circuit board (PCB) confirmed the first impression: This Fixed Income Securities calculator seems to be indeed an early prototype! Usually pre-series calculators have some modifications that were solved in a later stage but this FIS took it vice versa. The PCB looks exceptionally clean and misses the blue-wire and additional capacitor north of the LH5164 RAM. The TC54256 OTP-EPROM was tested apparently May 19, 1989, probably just days before the introduction of the calculator. The PCB itself is labeled REV.A / 2-89 while later models REV.I / 15-89 and REV. L / 35-90 document a lot of changes during the approximately 3 years of production cycle. 

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

© Joerg Woerner, May 8, 2008. No reprints without written permission.