[volt-nuts] 3458A Questions

[gbusg]

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 at att.net>
To: "'Discussion of precise voltage measurement'" <volt-nuts at 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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