I am thinking about adding a 3458A to my list of 'things to think about' and
was wondering if there were any suggestions about what things to consider
when trying to find one.

Any serial number ranges preferred?  Any way to find out when a particular
unit was manufactured?  'HP' or 'Agilent' on the front preferred?  Options
001 or 002 useful or desirable?

I have looked at the Agilent website and the five 'Modification Recommended'
Service Notes.  Also, someone told me that older units could easily add
Option 001 by simply plugging in additional (or different?) memory chips to
available sockets on the board but later units used surface mount chips and
then it was not possible to do that.  Perhaps a return to Agilent or
swapping a board would allow that.

I presume the addition of Option 002 would be simply a change of the
reference board with a re-calibration.

I would appreciate any information about what to consider and where to look
when shopping for a 3458A.

Joe

Re: Purchase of a used HP 3458A

Here are some things to consider:

1. Because the 3458A lifetime has already spanned 21 years, date of
   manufacture has a big influence on the real worth of a used 3458A, IMHO. HP
   / Agilent made many revisions to the 3458A over that time, including
   re-design of some boards. In particular the A5 Outboard Controller board was
   re-designed several times.

2. The s/n prefix indicates date of major revision, but this isn't a
   reliable way to estimate date of manufacture because HP / Agilent sometimes
   went very long times (years) between major revisions. For a better estimate
   of date of manufacturer, look at the date codes on the various I.C.s on
   various boards. Look for the newest date code you can find but excluding
   date codes on a specific board if its date codes are radically different
   than for other boards in the unit, hence the clue that particular board
   might have been replaced at some time. Another way to estimate the date of
   manufacture is to examine the 3458A's serial number suffix. For example
   serial numbers in the low 100s were made in 1988. Serial numbers in the tens
   of thousands were made many years later, after many hardware and firmware
   revisions. It might be nice to look for serial numbers above, say, 8000,
   although for the right price I'd certainly go for a lower serial number. The
   point is that older units are worth less than newer units, IMO.

3. As Poul-Henning points out, Option 002 probably isn't necessary because
   most non-Option 002 units have aged to the point that they now significantly
   exceed Option 002 specs. (Option 002 7V Reference drift was spec'd 4ppm /
   year, but it's my experience that even non-Option 002 units drift
   significantly less than that. Option 002 is a hand-selected LTZ1000 with low
   drift.)

4. Look for a unit with Firmware Rev 8 or above. You can determine this via
   the front panel command "Rev?". For the right price a unit having a lower
   Firmware Rev would still be a good deal, but the point is that the low
   Firmware Rev would be another sign of an older unit, probably having some
   older Rev boards and older parts inside as well. Note: In many cases an old
   unit might have been retrofitted with newer firmware, so later Firmware
   Revs, alone, are not proof of the date of manufacture.

5. The older A5 Controller boards used three Dallas Semiconductor NVRAM to
   store Cal Constants and DMM stored states. Those NVRAM I.C.s have
   non-replaceable internal batteries that were spec'd to last 10 years (but in
   practice probably last something like 14 years). If you end up with an older
   version A5 Controller board, as Poul-Henning points out, retrieve the
   constants in your old NVRAM before their batteries crash and it's too late.
   It's somewhat expensive and inconvenient to replace those three I.C.s, so a
   much newer unit having the latest version A5 board (HP p/n 03458-66547) is
   highly desirable and worth significantly more than older units, IMO. Note:
   older units can be retrofitted with the newer version A5 Controller by
   ordering Agilent Update Kit p/n -3458-80047. Note that the newer version A5
   Controller is completely redesigned and has user replaceable batteries.

6. Be sure to perform the Self Test from the front panel. The meter must
   pass Self Test or you're probably looking at a very expensive repair.

7. Additionally, if possible run a "Time Drift" test per Service Note
   3458A-18 to make sure your A3 A/D board is OK. If the meter fails this test,
   you're probably looking at an expensive A3 board repair.

Cheers!
Greg

----- Original Message -----
From: "J. L. Trantham" jltran@att.net
To: "'Discussion of precise voltage measurement'" volt-nuts@febo.com
Sent: Wednesday, September 21, 2011 6:49 AM
Subject: [volt-nuts] 3458A Questions

I am thinking about adding a 3458A to my list of 'things to think about' and
was wondering if there were any suggestions about what things to consider
when trying to find one.

Any serial number ranges preferred?  Any way to find out when a particular
unit was manufactured?  'HP' or 'Agilent' on the front preferred?  Options
001 or 002 useful or desirable?

I have looked at the Agilent website and the five 'Modification Recommended'
Service Notes.  Also, someone told me that older units could easily add
Option 001 by simply plugging in additional (or different?) memory chips to
available sockets on the board but later units used surface mount chips and
then it was not possible to do that.  Perhaps a return to Agilent or
swapping a board would allow that.

I presume the addition of Option 002 would be simply a change of the
reference board with a re-calibration.

I would appreciate any information about what to consider and where to look
when shopping for a 3458A.

Joe

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