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: [email protected] [mailto:[email protected]] 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 <[email protected]> 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 > <[email protected]> > 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: [email protected] [mailto:[email protected]] > > On Behalf Of Randy Evans > > Sent: Friday, 15 August 2014 1:22 PM > > To: [email protected] > > 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 > > _______________________________________________ > > volt-nuts mailing list -- [email protected] To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > and follow the instructions there. > > > > > > --- > > This email is free from viruses and malware because avast! Antivirus > > protection is active. > > http://www.avast.com > > > > _______________________________________________ > > volt-nuts mailing list -- [email protected] To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > and follow the instructions there. > > > _______________________________________________ > volt-nuts mailing list -- [email protected] To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
