Here we have two HP-41CX calculators used by mr. David Serisky in the HP Corvallis, OR factory for prototyping and probably other research work. I have acquired the calculators in an estate sale lot from a dealer in Salem, OR.

Here is what a former colleague of mr. Serisky says:

I knew David Serisky. He was one of the engineers I looked up to. I learned a lot from him, like how to draw an electrical schematic that clearly conveys the intent of the circuit. He’s a great engineer and it was my joy to work with him in those wonderful days. … I am so sorry to hear of Dave’s passing. He obviously died too young.

First photo of the “half back case” is probably a “test fixture” that Dave hand made from parts available in the R&D lab.  It is used to quickly test HP41 mother boards and allows oscilloscope access to the various signals for debugging.  The motherboard appears to be an HP41CX due to the presence of the 1LF6 and small 32768Hz quartz crystal for the time functions.

The other calculator serial number dates to 1979 which is a bit prior to my hire date.  My guess is HP had pondered using 42C instead of HP41CX and so you see the rear label marking as such.

Please note the unusual HP-42C label on the machine to the left; that is definitely not an artisanal label. The left machine is in a HP-41C housing (from the very, very early serial number, one of the earliest known serial numbers in fact, 1926A00172) nevertheless inside it is a HP-41CX. I deem this to be a prototype of the never-released (but often talked about) HP-42C. To my knowledge this is the only known artifact that exists outside of HP vaults that can be linked to this project.

The machine to the right has no serial number, the case is cut in half (very neatly) and the motherboard is held in place by two screws drilled directly through the screw posts used by a normal HP-41.

Both calculators work perfectly and are in excellent shape from all points of view.

Definitely a piece of history from the HP-41 era!

I have tried to obtain more information about this and in early 2019 I have listed the calculator on eBay hoping to get information. I got one single thing: someone remembered a PPC meeting in early 1980 where bootleg images of a HP-42C were circulated, but he could not really remember anything else. This seems to confirm that there was a 42C project about the time this machine was built which is early 1980s from the codes on the chips. The serial number is obviously not original, probably the builder used whatever case was handy at that time in the lab.

An image of an engineering prototype of the HP-41CX calculator exists in the Smithsonian museum, here: Hewlett-Packard HP-41CX Handheld Electronic Calculator, Engineering Model

Recently I have found out that there might be more to the subject than thought. It seems the Living Computer Museum and Labs (Seattle, WA) has a HP-42C machine! Here is a snapshot obtained by Jeff W. a couple of years ago. Here it is:

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