27 December 2018

HP 9403A first look inside

So .... time to look inside the HP 9403A device! I didn't do it in Friedrichshafen last June because the screwdriver I had was not the right fit and I was afraid to destroy the head. With the right tool it turned out that screws were secured with a dab of glue, then off they came easily. Once removed the thick aluminum top lid I was enchanted by the shining boards, gold plated ICs, perfectly grouped and routed wires as if it was build yesterday, while the thing is about 45 years old and has certainly passed few owners.

The absence of dust inside is easily explained: there are no holes, so no way out for the air and no way in for contaminants.

There is a lot of room inside, a power supply, an optional PSU, no microprocessor whatsoever at first glance. Board are mounted with servicing in mind, or mostly quick replacing. 90% of integrated circuits are branded HP and carry their specific mysterious 1820-xxxx part number. Unfortunately Nixies are hidden behind a part of the chassis and I cannot see their model. Nevermind. Since everything looks clean I decide to power it up.

As a precaution I screwed back the lid in place and brought the 9403A on the balcony so that exploding stuff would stay inside and any smoke would not pollute home. Well, I was not surprised that nothing bad happened and Nixies lit up:

1-2-3 ... 13 tubes! Neat. They have gas. Further experiments will tell if they have cathode poisoning or broken digits.
Any interaction with the keypad or front panel keys do not lead to any change on the displayed value. Given that there is no intelligent part inside I was expecting it too. Next step is accessing the Nixies to see their model.