Hi, IO540
Having been doing electronics design since the 1970s I am impressed by the survival of the data.
Look this
IMHO, either the memory chips are in a separate sealed module (which can itself withstand great pressure) or the cylindrical capsule did not leak.
And also this
The SSFDR CSMU (4700 model) used in F-GZCP was the cylindrical, steel armoured.
If however the PCB was encapsulated in a suitable epoxy, and this was done under a vacuum to avoid any air-filled voids (which would collapse under the 4km pressure and destroy the module) then the PCB could have survived the total immersion.
I guess they implemented a "double or even a triple barrier". Why not to do so?
It would be interesting to know how these things are made.
I am looking for and will come back on this subject
It's awfully hard to make a watertight package which can hold 4km pressure for 2 years and which uses just o-rings...
I have some "war surplus" and other newer parts with connectors integrated to the mechanical modules. I donīt see why to have an o ring in a CSMU.
When you was starting to design i was starting my EE graduation, so please consider my comments as a way to learn from you.