HP Nixie driver IC (HP 1820-0729)

The HP 9403A brought another set of Nixie driver chain ICs in my home. It was the HP take on the matter: custom ICs with hard to find pinouts, let alone a datasheet. Apparently with one positive side: the pinout was laid out to simplify PCB routing.

I found an HP 1820-0729 that is an updated version of HP 1820-0092. They are a sort of 74141/7441 BCD to decimal decoder and driver but obviously with different pinout.

Ahead of that there is an HP 1820-0116 that is a 4-bit latch.

HP 09403-60006 board with buffer, driver and Nixies.

I have got an idea where to look for pinouts, but it is another story.