[volt-nuts] Agilent 3458A Issues

[Randy Evans]

When I try to execute a 10V cal, I get an error code "209 HARDWARE FAILURE
- - INTERNAL OVERLOAD:31" I suspect that the unit has a different security
code than 3458.  I can't change it without opening up the unit, which I
don't want to do unless I decide to keep it.  Do you have any other
suggestions on how to check the A9 card?

On Sat, Nov 18, 2017 at 11:17 AM, Randy Evans <randyevans2688 at gmail.com>
wrote:

> Illya,
>
> That is a great idea.  I will give it a try.
>
> Thanks
>
> On Sat, Nov 18, 2017 at 4:47 AM, Illya Tsemenko <illya at xdevs.com> wrote:
>
>> Since you have 732A, testing should be easy enough. Calibrate faulty
>> meter for zero and DCV 10V to 732A, record CAL? 2,1 value. This is your LTZ
>> output. Then leave it running for few days to drift away and calibrate
>> again to same 732A. Check CAL? 2,1 again. Calculate the difference and if
>> it matches output drift (that 1.1ppm/day you mention) - you can be 80% sure
>> that A9 is a problem. Other 19% go to A1 and A3 circuits, as 7V is not used
>> directly in the meter, and there are still gain parts to get +12 and
>> -12VREF on A3 and 10Vish bipolar levels on A1. If your CAL? 2,1 stays same
>> (within 0.3ppm) then A9 is fine.
>>
>>
>> On November 18, 2017 12:59:53 PM GMT+08:00, Randy Evans <
>> randyevans2688 at gmail.com> wrote:
>>>
>>> I just received an Agilent 3458A that has a problem with noise and a
>>> drifting voltage measurements.  I am using two Fluke 732As to compare
>>> absolute voltage measurements over time against the Agilent and an HP
>>> 3458A.  The HP unit has a new A3 ADC card and seems to be very stable and
>>> low noise, so is being used for comparison.  I have been doing simultaneous
>>> absolute voltage measurements and DC Cal Constant measurements several
>>> times a day and then calculating the drift rates of the two units using the
>>> HP Service Note 18 procedure.
>>>
>>>
>>>
>>> The results indicate the Cal Constant drift rate of both units is very
>>> similar and within spec per Service Note 18.  However, the absolute value
>>> measurements show the Agilent unit changing 1.1 ppm over a day whereas the
>>> HP unit is within a tenth of a ppm over a day.  In my way of thinking the
>>> Cal Constant procedure assumes the voltage reference board in the 3458A is
>>> stable, hence the absolute value reading should remain essentially constant
>>> after each ACAL DCV, which is the case with the HP unit.  Since the Agilent
>>> unit shows a steady drift in the absolute reading, this would indicate to
>>> me that the voltage reference board is likely the cause of the problem, and
>>> is also likely the cause of the noisy readings.  If so, this is a
>>> “relatively” easy fix (I have several 3458A voltage reference boards, one
>>> of which has been continuously powered up for several years).
>>>
>>>
>>>
>>> The issue is that I have to make a decision to keep or return the Agilent.
>>> It has a cal seal on it and if I open the unit up to change the voltage
>>> reference board, I own it and can’t return it.  I would appreciate an
>>> opinion from the members of the group as to what they think the odds are
>>> that the voltage reference board is the source of the problems with the
>>> Agilent 3458A.
>>>
>>>
>>>
>>> Thanks,
>>>
>>>
>>>
>>> Randy Evans
>>>
>>>
>