I'm collecting a history of this DVM. Does anyone have any other resources, know of specifics, can check the accuracy of what I've already listed, and have personal anecdotes of their experience with this DVM? Items marked ? are considered uncertain and a question for the group. ------- begin history outline ----------- The HP 3456a was introduced into the product line in a feature article in HP Journal April, 1981. 3 of its engineers co-wrote the article. Charles A. Clark developed the true-rms converter. Jim Ressmeyer did thin-film hybrids and analog design for voltmeters, including the 3455A DVM; he was responsible for the ohms, input filter, and front-end switching sections. Larry Jones worked on the dc section. The 3456a entered the HP catalog in 1981 and listed for $3500. It was later incorporated as an optional DVM for the HP 3054c data acquisition system, until it was discontinued. Catalog Highlights: 1986 3456a listed for $4000 3457a first introduced into the catalog and listed for $2800 1989 3458a was introduced for $6000 1993 3456a Last listed for $6400 During its production run several versions were made, but a large number of internal changes were in the 2015A serial number series, and all changes are documented in the HP 3456a Service and Calibration manual. There were no changes to performance specifications from the original design of 1981. The service manual at Agilent's website refers to the 2201A series and prior models. Circuit operations characteristics as described by Clark, Ressmeyer and Jones in their paper are described in the service manual, with far more detail, particularly in the 'theory of operation'. 2015A Series NB: notifiable features Cooling fan and air filter in rear panel ROM model changes 2201A Series NB: noticeable features Fan and filter now absent power regulator LM323K exposed on rear panel 2512A Series NB: noticeable features Introduction of soft mechanical switches replace the original hard tactile-feedback switches on front panel ? 2943A Series NB: noticeable features Last series prior to being discontinued ? Notations by other individuals regarding 3456a, about device failures other than from physical abuse or electrical accident: ROM failures Stepan Novotill posted a detailed repair note on the failed PROMs in the 3456a. 2015A series is primarily affected ?? A series appeared on the yahoogroup, hp_agilent_equipment, in 2007, but no further threads have appeared before or after it. Q: Have other serial numbers been affected, anyone with personal experience? Other Failures A common failure [ but rare reports] in the 3456a are capacitor failures in the power supply. It affects all models, older ones and unused ones more common that those in actual service? I've person experience with failed power supplies in 2 3456a each in the 2015A and 2201A series. References: L.T. Jones, J Ressmeyer, C.A. Clark. "Precision DVM Has Wide Dynamic Range and High Systems Speed," HP Journal. Vol. 32, no. 4, pp. 23-32. April 1981. Sincerely, Marv Gozum Philadelphia, PA