[volt-nuts] New HP3458A

Sat Aug 16 08:48:40 EDT 2014

Randy,

Congratulations on your 'new' 3458A.

The 'CALRAM' back-up was just recently covered.  There are two options:  

1.  Remove the NVRAM, read its contents with a programmer, program a new
NVRAM and install the new NVRAM.  I chose that option, installing sockets
for the 'CALRAM' and the two other NVRAM's that are used for other,
non-calibration, purposes.  Be sure to let the NVRAM cool all the way down
before trying to read it.  Learned by experience with that one.

2.  Read the 'CALRAM' via HPIB and the MREAD command (many steps involved
but can be done as a program with your laptop/desktop), use that data to
program a new NVRAM (I suspect there is a way to 'program' the NVRAM by HPIB
as well but I don't recall ever reading anything about it on the list),
remove the old NVRAM and install the new NVRAM.

When I read the contents of the 'CALRAM' with a programmer and with the
MREAD command, they matched exactly.  However, when you do an ACAL, the
CALRAM contents change.

Does your unit have the single EPROM or the 6 EPROM version of the firmware?
Also what version of firmware do you have?  The latest is REV 9.  REV 8 is
'out there' on the net.  If you purchase an exchange display, and you have
the single EPROM version of the A5 Outguard Controller Assembly, the REV 9
EPROM is $24.10 per the Keysight website.  Might be worth adding to the
order.   The 6 EPROM version is $220.

Also, what is the serial number?  You can get a good idea of age by the
serial number.  Also, the various covers inside often will have dates of
manufacture on them and the chips, etc., will have date codes, including the
NVRAM's.

Also, you can add option 001 by plugging some memory chips, specific details
I don't recall right now.

As far as the reading when shorted, I recall the Calibration Manual calls
for a piece of copper wire to short the input terminals.  It looks like a
flying 'U' when properly fashioned.  The Calibration Manual gives the
details, IIRC.

Good luck.

Joe

-----Original Message-----
From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On
Behalf Of Randy Evans
Sent: Friday, August 15, 2014 8:40 PM
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] New HP3458A

I would like to thank everyone that replied to my query on what to look for
in my "new" HP-3458.  I did find that the AUTO ZERO button does work fine,
thanks to Bill's comments.  I had looked in the manual, just not far enough.

The display is still perfectly readable but i would like it to be "perfect".
I am particularly interested in the exchange display for $272 (better than
$700 for a new one, as Todd suggested).  Does someone have a contact number
at Keysight that I could call (my experience is that one can spend a lot of
time calling around until the right person is finally found).

I certainly need to figure out how to copy and replace  the NVRAM - I lost
the calibration on my Datron 1082 by not realizing the memory backup battery
died and now I need to calibrate it myself (the HP3458A should make that
doable, I hope).  Any suggestions would be greatly appreciated.  I believe
it has been covered before on Volt-Nuts and I need to go through the past
discussions to find it.

One question I have for the group is what should the display typically show
with the input shorted?  I see a reading of about -.0025 mV.  That seems
rather high.  I tried several different banana cables (gold plated, tin
plated) used to short the input terminals  to see if thermocouple effects
might be responsible but there was no change in the reading.

Still learning.

Thanks,

Randy

On Fri, Aug 15, 2014 at 8:06 AM, Jason Watson <watson.jason at gmail.com>
wrote:

> I've also seen excessive Guard to Low leakage when varistor RV501 has 
> gone bad (it's located on the front/rear switch pcb and it's possible 
> to replace it while leaving the circuit board in place if you are
careful).
>  HP/Agilent/Keysight Part number is 0837-0196, cross referenced to a 
> Harris Corp. V430MA3A.
>
>
> On Fri, Aug 15, 2014 at 10:46 AM, Stephen Grady 
> <grady.steve at gmail.com>
> wrote:
>
> > Randy,
> >
> > I have come across a few 3458A's that had leakage between Guard and 
> > Low when te guard is in external guard position. This was due to a 
> > leaky external guard switch and/or leaky front rear switch. This can 
> > be quickly
> determined
> > by measuring resistance between guard and low with guard external. 
> > This normally in not an issue except when you are using 3458A to 
> > measure
> voltage
> > with low above earth potential say in a bridge the guard low leakage 
> > will be loading other arm of the bridge.
> >
> > Kind Regards,
> >
> > Steve Grady
> > Sydney, Australia
> >
> > -----Original Message-----
> > From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] 
> > On Behalf Of Randy Evans
> > Sent: Friday, 15 August 2014 1:22 PM
> > To: volt-nuts at febo.com
> > Subject: [volt-nuts] New HP3458A
> >
> > I picked up a used HP3458A today, which I needed for some precision 
> > DC measurements i need to make. It passes all the self tests and the 
> > Auto
> Cal
> > but is there any thing else I can check ( I have a 14 day RR).  It 
> > reads
> a
> > 10V standard I made within a few tens of ppm, but it's not a 732A 
> > but
> that
> > is at least comforting.  It also reads an ESI 10Kohm standard 
> > resistor
> dead
> > on.
> >
> > The only problem is that the display has some faint pixels in some 
> > locations, with three in the second row for every digit location dead.
> >  Likely a pixel driver I would think.
> >
> >  I am not too familiar with it yet but I noticed when I push the 
> > auto
> zero
> > button, the display has a blinking square until I hit a measurement 
> > mode button; e.g., DCV, ACV, OHM, etc.  Is this normal?
> >
> > Regards,
> >
> > Randy Evans
> > _______________________________________________
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