Desktop tech of 1969: under the covers of a Compucorp calculator

January 28, 2015 // By Michael Dunn, EDN
Nowadays, there are endless venues for a youngster to get into programming. In the early and mid 1970s – less so! Thus, as best as my grey matter can recall, it was a desktop programmable calculator that became my first digital servant, sometime around 1977.

My high school had two or three Compucorp machines – perhaps the 125E Scientist, though I think at least one machine had a Nixie display, not a printer. Now, years later, I find a Monroe 1655 in my "museum," waiting to give up its secrets.

Monroe? Compucorp? What's the connection? It seems, according to the Compucorp page linked above, that the Monroe machines predate Compucorp. One of the boards in my Monroe is stamped with a copyright notice – 1969 Computer Design Corp – of the company who developed the machine for the already long-established Monroe. Only a couple of years later did they start selling machines themselves under the Compucorp name. The date codes in my machine point to a 1970 or 1971 build date. The LSI is made by AMI (which was bought by Motorola – I mean, OnSemi – in 2007).

The bulk of the circuitry for the 1655 consists of 31 LSI chips. I could make guesses as to which are ROM, RAM, and logic, but why don't you? Other components appear to handle power, display driving, and keyboard interface.

That's Mister e to you! Buttons on the top row are related to programming.


The cover removed.

The power supply board (it sits behind the display board). The orange electrolytic is for the HV Nixie supply.

next; vintage logic pcbs...