Randy,

I have had two 3458a that had bad front / rear switches. It was easy to determine during the calibration of the Cal 0 that failed. A copper short across both of the inputs, as per the calibration procedure, showed more than .5 ohm in 2-wire mode on the lowest range. The resistance was not stable and seemed to settle slowly. The switches were available and not hard to replace but probably not something I would attempt with a ROR unit.

The pixels can have some burn-in, but I don't know if Agilent/Keysight would fail a cal for dead pixels. There was no indication that they looked at this during the calibration. They use the GPIB port and probably would fail it if the display was not readable during self-test. A call to Keysight would probably help. I think the displays are in the $700+ range. That reminds me, you should check the GPIB port. Mine was not functioning when Agilent received the meter, but then it started working when they bench tested it. It almost cost me $2700 .

The ACAL ALL passing all tests would be a good sign, but I am not sure if it indicates that the SCAL calibrations will pass. Someone else can probably help with that potential issue.

The age of the NVRAM is important. Can you determine when they were replaced ?

Todd
Sent from my iPad

Randy:

The blinking square when you push auto zero is perfectly normal.  It is

now waiting for you to give it an answer. By pushing either the "^" up arrow
or "v" or down arrow on the keypad set located below the display on the
lower row left side, you will get the menu options for auto zero of "ON",
"OFF" or "ONCE".  You make your selection and then press the "ENTER" key on
the "MENU/USER" keypad set, lower row right hand side.  The 3458A has a
large set of measurement options that you can select.  Read the manual.
These are accessed either through the IEEE-488 or the front panel keypads.
You can get a refurbished "display" PCB from Keysight for $272 exchange
which should cure all of your display problems.  P/N 03458-66517.  It is
easy to replace.  Read the manual.  Check the Keysight website for details.
SCAL is difficult to check without special equipment such as a AC/DC thermal
converter.  The NVRAM can be an issue depending upon the date codes on the
NVRAM devices.  Replacing them is time consuming but can be done.  But you
lose your calibration unless you can read the old ones and then program the
new ones.  Be sure to put in sockets when you replace the NVRAM.  Why HP
didn't do this is beyond me.  Precision machined sockets hold the NVRAMS so
tightly that it is almost impossible to get them out.  Someone suggested
that the weight of the NVRAM devices might allow them to come out of the
sockets during shipment but I just don't see how with the proper sockets.
It sounds like DC and Ohms are working OK.  Passing self test is a good
sign.

Bill

----- Original Message -----
From: "Randy Evans" randyevans2688@gmail.com
To: volt-nuts@febo.com
Sent: Thursday, August 14, 2014 8:22 PM
Subject: [volt-nuts] New HP3458A

dead

https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts

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@gmail.com
wrote:

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@gmail.com
wrote:

I've used these
http://www.ebay.com/itm/4mm-Solderless-Stackable-Banana-Plugs-1-Pair-Red-Black-/171030386766
connected with these wires
http://www.ebay.com/itm/One-Pair-of-16-AWG-16-Gauge-Silicone-Wires-Silicon-Cables-1m-Red-1m-Black-/200893010111
and have had good luck, although I have not been doing any precision
voltage work. Franky Tong is an excellent vendor, and delivery has been
quite fast. He also offers a solder version of the banana plugs
http://www.ebay.com/itm/4mm-Stackable-Banana-Plugs-1-Pair-Red-Black-/171062979200
.

Gordon

On Fri, Aug 15, 2014 at 6:44 PM, Tony vnuts@toneh.demon.co.uk wrote:

Randy,

I have not been able to do accurate work with banana plugs. Too much
thermal mass. For best results use  copper wires into the cross holes of
the banana jacks or small gold plated copper spade lugs crimped on the
ends of the test leads. Cheap at Radio Shack.  Both work fine. Remember
to do an ACAL every time you want accuracy. I think my 3458A is about +5
PPM/C  for four wire resistance (10K ohm) on differences of Temp?.  Also
clean your air filter and record the Temp? after so you know when to
clean it again. If you try to use high impedance resistance standards
(L&N Cheap ones) they will not measure correctly unless DELAY = 10
seconds on my system.

Charlie

On 8/15/2014 6:39 PM, Randy Evans wrote:

Tony,

I have looked for the perfect connector for all types of measurements. I
came to the conclusion that the type of measurement will dictate the type
of connector. I prefer the solder type and would never consider using a
screw type for any of my cables. I am sure they have an application
somewhere, but it gives me peace of mind knowing that the cables won't pop
out and create a hazardous situation. I have read that for low level
measurements, use a direct wire connection, or a low thermal spade lug that
has an air-tight crimp and then soldered for strength. This is not cheap to
build, the crimp tool can be very expensive.

I have found that Multi-Contact makes a good range of plugs as an
alternative to Pomona. I recently purchased some of the SLS425-SE/Q for
some generic sheathed cables. These are made of gold plated brass and are
rated to 1kV and max 32A. These look heavy duty but not too expensive.

The SLS205 series looks to be a decent low voltage test connector. I do not
have any experience with these connectors but you might want to make some
cheaper jumper cables for power supplies. The LK425-Z is another low
voltage but higher current than the previous connector. It is the only
sheathed, retractable, stackable connector that I have found from a
reputable company.

The silicone cable is probably the best choice of cable to use with any of
these connectors. Pomona sells the cable #6733 in red and black. You may
also want to consider shielded cable with an external ground/guard
connection. I have a couple sets of the Fluke 5440A-7002 cables and I can
tell the difference using them in high resistance measurements compared to
the Pomona 5290A low thermal cables.

I have been waiting to build a couple sets of Fluke 5440A-7003 test cables.
I have some Belden 8719 cable, gold plated copper spade lugs from JS
Willey, and some generic blue pomona patch cables that will be cut in half.
The crimp tool is more expensive than all the other components.
Unfortunately, I could not find a better alternative for the low ohms
measurements.

Check Farnell for the Multi-Contact connectors. I had no trouble finding
them on the Newark site. The cost will probably be twice what you want to
pay, but you can build them to your specs so you can make them as short or
long as needed.

Todd

On Fri, Aug 15, 2014 at 7:44 PM, Tony vnuts@toneh.demon.co.uk wrote: