Montgomery Ward P8F aka TXI-8644A

Date of introduction:  August 1, 1973 Display technology:  LED-modules + lens
New price:  $59.50 Display size:  8
Size:  5.7" x 3.1" x 1.6"
 146 x 79 x 41 mm3
Weight:  5.1 ounces, 144 grams Serial No:  37X-0002843
Batteries:  4*AA Date of manufacture:  
AC-Adapter:   Origin of manufacture:  USA
Precision:  8 Integrated circuits:  TMS0103
Program steps:   Courtesy of:  João Oliveira

TXI-8644A_Back.jpg (215340 Byte)This neat calculator does not look like a Texas Instruments product. To identify it, you have to know more about the coding used by Montgomery Ward:

Models starting with

• TXI were manufactured by Texas Instruments
• DAN were imported by APF Electronics, Inc.
• DNS were manufactured by National Semiconductor (later Novus)
• EKJ were imported by Kings Point Corporation
• GLE were manufactured by Lloyd's Electronics, Inc.

An identical housing was used for both the P8P alias TXI-8645A and the P8M alias TXI-8646A calculators. The printed circuit board and the serial number of the calculator gives you another information: Late P8F calculators (e.g. 37X-0026077 from Thomas Brockmeier) carry a PCB with a marking P8F/P8P. Okay, the same PCB in two calculators. Please compare this serial number with the P8P: 37X-0066692. Let's assume that the P8P replaced the P8F in the year 1974 and the happy customer got the %-key for free.

Dismantling this P8F reveals another surprise: The printed circuit board (PCB) carries a magic number that links to a lot of other calculators like the Radio Shack EC-300 and EC-1000.

The printed circuit board of the P8F looks like most calculator based on the TMS0100 single-chip calculator circuit. Just a LED-display, some driver circuits and a DC/DC-converter to generate the power supply.
More important is the number etched in the PCB:
TXI-8644A_PCB.jpg (65902 Byte)
The small display board uses LED-modules with just one digit per module. Once again the magic number:
TXI-8644A_DSP1.jpg (24505 Byte)
The components side of the display board sports the logo of Texas Instruments etched in the PCB:
13-04-709-xxx numbers were used by TI!
TXI-8644A_DSP.jpg (19337 Byte)

This calculator looks very unfamiliar compared to other Texas Instruments calculators. Notice the combined [-=] and [+=] keys not known from calculators sold by TI.

Don't miss the rare TXI-8661A based on the Exactra 23 calculator.

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