Teardown: 1966 Programmable scientific calculator

Michael Dunn

EDN

I've taken a screwdriver to my rare and wonderful Wang LOCI-2 calculator…

This machine's design seems to be from 1965, though I estimate mine was made in 1967, the same year Young-Me trundled off on a barely-remembered trip to Expo '67 in Montréal.

Teardown: 1966 Programmable scientific calculator

It's a remarkable design achievement. Using over 1,000 transistors (and not a single IC), it manages to implement log and antilog functions, and in turn leverages those to perform squares and square roots, multiplication, division, and more. It also has a 16-register core memory, a 10-digit Nixie display, and is programmable!

Teardown: 1966 Programmable scientific calculator
The top-view Nixie displays.

What memory technology is used for program storage, you ask? Paper! Yes – good old paper punchcards, except the card reader doesn't pull a card through and store its contents in RAM. The card itself is the RAM (well, ROM), and the card reader has a contact at every possible hole position. The card is read directly as the program executes. If you're wondering, the original selling price was about $3,000 – automobile range then!

Teardown: 1966 Programmable scientific calculator
The four-plane core memory module. Note the twisted pairs.
Teardown: 1966 Programmable scientific calculator
The card-cage. Each card is unique.

Apart from a general cleanup, I haven't done any restoration work yet. The machine lights up and responds to keypresses, but doesn't work too well. Clearly, it needs to get onto the lab bench, and the good scope needs to be fired up. Maybe all it will need is a new power supply filter capacitor.

Teardown: 1966 Programmable scientific calculator
The "Ken" seal of approval.

The PCBs themselves are interesting: double-sided, yet no component-side pads unless they're needed as a via.

Teardown: 1966 Programmable scientific calculator Teardown: 1966 Programmable scientific calculator
This board has a 1965 date in copper. I wonder what those bus lines are?
Teardown: 1966 Programmable scientific calculator Teardown: 1966 Programmable scientific calculator
I'm ready for my closeup. Yet another board. They all look similar to this.

EDN

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