I recently purchased this rare HP item off of eBay. It appears to be a trade show demonstration unit for selling HP's alphanumeric LED display modules. It is from 1970 (based on the date codes of the parts) and is made to a very high standard. As received it needed a very good cleaning to remove "residue of rodents" but once cleaned seemed to basically work without any repairs. The only remaining problem is a worn-out "DATA ENTER" switch but I found an exact replacement on eBay and will get that going as soon as the part arrives.
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This same unit is on page 3 of the July 1970 HP Journal () and the corresponding article describes it in pretty good detail, although without schematics. All the ICs appear standard except for a mask ROM, and, of course, the HP display module itself.
I am posting this here to document this rare item's existence and in the hopes that a former HP employee may be able to provide some more information on it.
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medasaro