Digi-Matic EM-8 Calculator Internals
August 28, 2024
The Digi-Matic EM-8 was a mains powered desktop calculator licensed by Simpsons-Sears and manufactured in Japan in the mid-late 1970s. It sported a nine figure vacuum fluorescent display with calculator functions driven by a Western Digital LC1552-B calculator on a chip IC. Because of the IC used in this calculator the design itself is quite simple.
The main LC1552-B is socketed, this one manufactured mid-1975.
The nine digit display looks good.
The keys are contained within a removeable housing.
Since the calculator was already working, the job at hand was to simply clean it out, and replace some of the missing feet on the bottom. While inside I took the opportunity to review the electrolytic capacitors and replace them, as well as test the resistors to ensure that they were in a reasonable range.
The key tops are spring loaded and in turn activate a plastic plunger which contains it's own spring, which then presses in a metal formed spring to close contacts on the board. Despite the intricate mechanism the keys worked very well, and a cleaning of the board contacts ensured that they were all making good contact.
Here is the complete collection of keys and springs, and in the top left you can see the metal formed springs which create the final connection to the board.
After cleaning everything, replacing the capacitors and rubber feet and testing the remaining components, the calculator was reassembled and tested, looking as good as it did when it came off the assembly line.
