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The HP 9845 was an inflection point for HP - the last of the programmable “desktop calculators” using their proprietary NMOS technology before they went to the Motorola 68K family, but also the first of the true desktop graphics workstations. For a deep appreciation of these machines and all that went into them, be sure to visit the HP 9845 Project, Ansgar Keukes' incredible website -

Machines in the Computerarium collection:


These three machines were received in a group as a donation from the Eventide Corporation and had been used by them as scientific calculators, process controllers and laboratory test beds for their products, including a line of memory products and HPIB multiplexors. Parts seem to have been swapped among the machines at different times. When I received them, the 9845C had the proper Option 200 power supply but the 9845T had an Option 100 power supply, underpowered for that configuration, and the 9845B lacked a power supply altogether. The only monitor received with the group was a 98780 enhanced monochrome display for the 9845T.

As part of the restoration process, the Option 100 power supply has been returned to the 9845B and the Option 200 power supply has been transferred to the 9845T. A standard monochrome monitor has also been obtained so now I'm working on restoring the two monochrome machines and the 9845C project is currently sidelined.

RIFA resin-encapsulated “safety” capacitors - a common vintage computer component and source of problems - were used in the AC power inlet module of the 9845s as well as in the 9845 power supplies. After the inlet filter in the 9845T failed in a dramatic and unpleasant release of smoke, I rebuilt the filter and then replaced the similar units in both power supplies.

AC inlet module rebuild for 9845T-1838A06653
Option 100 power supply recap
Option 200 power supply recap


hp_9845.txt · Last modified: 2018/09/10 23:03 by cic