This calculator is an example of how popular it was in the early '70's to get into the calculator business. Many companies sprouted up in this timeframe to satisfy a very demanding market. And, many of these companies died off almost as fast as they came along in the big shakeout of the calculator market in the late '70's and early '80's, as inexpensive battery-powered, handheld calculators mostly evaporated the market for AC-only desktop calculators. This machine, a duplicate of the much more well-known APF Mark I, was made in Hong Kong by APF in the early 1973 timeframe. APF had a manufacturing facility in Hong Kond where these calculators were made with various diffrent brand identities under OEM agreements with APF. APF would manufacture the calculators complete, and ship them in quantity to the OEM customer, who would apply their own branding and model/serial number tag, and sell the machines through their own marketing channels.
Quick Reference Guide and ID Tag on Passport CA 850
With the advent of Large Scale Integration (LSI) single-chip calculator designs, and at that time, still relatively inexpensive labor costs in Hong Kong, the "generic" calculator became a reality. APF would build inexpensive desktop machines such as this, with an open space on the top of the cabinet for a name plate, and a space on the back panel for a model/serial number tag, and sell them like hotcakes to the various entrepreneurs around the world who thought that getting into the calculator biz was a quick way to get rich. The only things that a prospective calculator company would have to do is establish a marketing presence, create advertising, set up an inventory of spares as warranty replacements, and a basic finance function, and they would be off to the races. With an OEM contract like that forged with APF all that the retailer would have to do is stick a nameplate and serial number tag on the machine and provide it to retailers to sell the machines to an eager marketplace.
Internal view of Passport CA 850
The Passport CA 850 is a very basic 8-digit four function desktop calculator. It runs on AC power only and uses neon gas-discharge seven-segment tubes for display. The machine operates in switch-selectable floating decimal or can be set to fixed decimal point locations of 2, 3, 4, or 5 digits behind the decimal point. Another slide switch turns the constant [K] function on or off.
A closer view of Gas-Discharge Display and Driver Circuits
Internally, the CA 850 is very simple. It is based on the Texas Instruments TMS0101 single-chip calculator LSI. The 9-tube gas-discharge tube display is driven by discrete transistor drivers. Gas-discharge tubes work on the same principle as Nixie tubes but rather than have electrodes in the shape of the digits, the electrodes are grouped into the now-familiar seven-segment arrangement. This arrangement required fewer interconnections, was easier to multiplex, and the tubes were less expensive to manufacture than Nixie tubes. The display tubes are grouped together and held in place by a plastic frame.
Detail of Gas-Discharge Display Tubes in Operation (note 'C' Overflow Indication)
The display tubes are wired to a small auxiliary circuit board that has hand-wired connections to the main board. The left-most display tube, while a standard seven-segment display tube, is used for indicating error/overflow, and negative sign indication. An overflow results in a 'C' being displayed, with a negative overflow showing up as 'E'. Division by zero also results in an overflow indication. The overflow condition shows the most significant eight digits of the result, but the only way to unlock the machine after an overflow is to press the [C] key to clear the calculator. The [CE] key allows erroneous numeric entries to be cleared from the display. The remainder of components in the machine are all discrete, with a clock generator, power supply regulation, and display driver components completing the circuitry. The keyboard assembly is wired to an edge-connector that plugs into the main board of the calculator. The keyboard appears to use key modules that contain magnetic reed-switches as the switching element.
Profile view of the Passport CA 850
The Passport CA 850 is relatively fast, with the 99,999,999÷1 benchmark taking about 1/10 of a second. During calculation, the tubes are not blanked, but calculations occur quickly enough that all that is really perceived is a slight flicker of the digits as the result is generated.