Article by Ken Shirriff on reverse engineering the precision op amps used in this analog computer to restore it.
We are restoring a vintage1 computer that CuriousMarc recently obtained. Analog computers were formerly popular for fast scientific computation, but pretty much died out in the 1970s. They are interesting, though, as a completely different computing paradigm from digital computers. In this blog post, I’m going to focus on the op amps used in Marc’s analog computer, a Simulators Inc. model 240.
You might wonder why I’m studying the circuitry of this analog computer in such detail. The reason is that we’re trying to restore the computer, but we don’t have documentation.10 11 Thus, I’m reverse-engineering it to determine how to restore it to operating condition and how to program it. While the circuit boards are not too complex, the computer contains many different boards to analyze. The hardest part is figuring out the connectivity of the many tightly-bundled wiring harnesses, mostly by brute-force beeping out connections with a multimeter.