Black magic, thy name is HP!
Great pics, thanks for sharing !
If I'm not mistaken, there are some precision trimmed caps on there too.
What kind of process is that, where they seem to screen-print the traces, the resistors and some kind of insulating bridges and also the dielectric for the capacitors? Does anyone know?
You can see where they built it with the RC network shorted out by fused links, probably used the ATE to first test that it had continuity from the board to the probes, then zapped all the fuses, and trimmed the RC network for each probe tip using some test signals for maximum bandwidth.
oldskool HP Voodoo Magic, I say