Disclaimer: this is a modified cross-post of my post on the Worldbuilding SE site, adapted to better fit the Space Exploration community.
A Von Neumann Probe (VNP) is a sci-fi probe which explores the universe in a self-replicating fashion: it finds a location to recreate itself, does the necessary mining and processing to duplicate every part of itself, and then sends off the duplicate to start the cycle anew. VNPs have been associated with the Fermi Paradox.
Investigations into assembly I know of
There have been various explorations into the idea of a VNP, which varying degrees of scope. Importantly, all of them seem to have the fundamental barrier of silicon chip production.
- NASA's Advanced Automation for Space Missions project - a deep-dive into the feasibility of creating a self-replicating factory on the moon. Most components were theoretically capable of being manufactured in situ, but in terms of electronics, Wikipedia describes that "a more speculative, more complex microchip fabricator was specified to produce the computer and electronic systems, but the designers also said that it might prove practical to ship the chips from Earth as if they were "vitamins.""
- RepRap and Snappy: 3D printed 3D printers - These projects are quite cool, but they are limited in that they're unable to print any of the electronics. Snappy, for example, has peaked at around 70% 3D printed parts. I assume this problem would exist for CNC'd CNCs and metal-sintered metal sintering machines too.
The way I see it, producing silicon chips is far from being achievable for a VNP at this point in technology, since producing a full-scale clean room and electronics factory would take a VNP the size of cities or larger. I will assume graphene electronics technology is impractical as well, since that's still in its infancy and would probably need clean room conditions as well.
With this in mind, are there any somewhat practical alternates to silicon electronics that could be used for a VNP? Vacuum tube technology, pneumatic instead of electric transistors, mechanical computers, something else? Emphasis on the practicality of the designs.