Teardown: 1966 Programmable scientific calculator

August 12, 2014 // By 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.

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!

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!

The four-plane core memory module. Note the twisted pairs.

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.

next; PCB close-ups...