Agilent 3458A - I joined the club - Page 1
Forum section: electronics / general

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 21, 2025, 09:06:38 am
content: I just recently picked up my first 3458A, it's an Agilent unit, with serial US2802xxxI found it in a test equipment shop in Akihabara, and with a quick email negotiation, managed to get it for 550,000yen, down from the original quote of 600,000yen+tax (for an original total of 660,000yen). Not a bad discount, especially as it has been factory calibrated in 2021 and 2022, so I'm in the process of trying to get my hands on those reports from Keysight.The only problem with it is apparently aslightlyhigh reading in the -1A range, but it's close enough that a cal might be able to fix it. Unless anyone thinks I should have a poke at it before I sent it to Keysight for calibration and adjustment? (Once my bank account recovers.....)So far, I have given it a clean, including cleaning and oiling the filthy fan. Ordered a set of HM62256BLP-10 RAM chips from a local seller to upgrade to Option 001, and started making a list of stuff to buy.I'll also be ordering a few FRAM adapters and parts to ditch the Dallas NVRAM's (I already backed up the calibration constants twice), and I'll socket U110 and update the firmware to v9 (I picked up a 40-pin socket today)I'm also thinking of replacing the fan with a Papst 612NLE, which seems to be the closest replacement to the original 612L I can find, and replacing the electrolytic and any RIFA capacitors (pending checking for any).The display is a bit worn as expected for it's age, I may or may not bite the bullet with a new VFD from China... Same with a new front panel plastic from Keysight. The plastic on mine is in pretty good condition, but I did have to apply a little bit of superglue on the corners, so these two parts are on the 'wish list'.It agrees perfectly with my 3-year-since-last-cal 34461A on 10V and 30K that I tried so far. Until now the Fluke 731B was only adjusted to my 34461A, but now I can really dial it in.So, feel free to educate me on using this instrument and any other things I should be looking at while I'm poking around, and also how to measure drift and performance and stuff, I haveno ideabut am willing to learn!

author: srb1954
author_rank: Super Contributor
timestamp: January 21, 2025, 09:26:51 am
content: Congratulations on joining the club.When looking for RIFA capacitors also check the mains inlet filter. If it is a pre-2000 Schaffner unit that may also contain exploding capacitors and it is best to replace it to avoid the risk of the awful stench the filter produces when those internal capacitors explode.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: January 21, 2025, 10:40:50 am
content: Very nice, i'm a bit envious, I would love a 3458A, I currently only have the Advantest R6581T, which is not bad, but not great either.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 21, 2025, 10:50:23 am
content: Reading low on the 1 A range is a bit odd. With the ACAL procedure there is no additional calibration factor that is applied. So the error there would be some kind of error in the ACAL procedure, like some thermal effect or not so perfect ground current compensation. Another possible source could be a relatively high TC for the shunt and self heating effect at the shunt.As a test it may be worth to look at the CAL constants that ACAL calculates for the 1 A range for a few repeated ACAL runs. When done at somewhat variable temperature one could also get an idea on the TC of the shunt.Before sending the unit in for calibration, I would use and test it for quite some time. It takes some time to recover from longer idle time. A point to test is also the ADC drift according to the SN18 service note. So read the CAL72? constant (and ideally also the temperature) after doing ACAL over a few weeks.

author: Dr. Frank
author_rank: Super Contributor
timestamp: January 21, 2025, 10:51:45 am
content: Congratulations!About 3400 €, that's a very good price, provided that its U180 is good.. but vintage 2000 (like mine, but from HP) should be good in this aspect, anyway.The 1A range is auto-calibrated only, it can't be adjusted by an external CAL (which would only adjust/calibrate 10VDC and 10kOhm).It's strange that it didn't pass the verification, could have been a problem with the calibrator.Has this cal report been provided by Agilent, or by an external lab?The limits look odd, as they are not centered, they are asymmetric.. strange.I have several test reports from other instruments, I'll have a look what's going on.My instrument still has OK capacitors, and the RIFAs seem so be still fine .. the Schaffner did not blow up yet..So, before replacing thoughtlessly, check visually and measure capacitance and ESR first.Don't you have any possibility to access any precise 10V and 10kOhm from another volt-nuts at your location?Calibration @ KS is unnecessarily expensive, only because it's a 3458A, and always be aware, that no DMM is regarded as a "standard".Setting up your own bank of 10V/10kOhm standards would be better, technically and economically.You need better cables for precise measurements, like PTFE with copper lugs, and you need a lab with constant room temperature, otherwise you can't make any use of the 3458As stability and uncertainty.FrankPS: Don't worry about the asymmetry of the 1A range.. that seems to be an offset, which HPAK probably never properly addressed in their calibration/validation routine. I looked into other reports directly from HP, Agilent and Keysight, and this asymmetry is not as prominent as in your case.Especially the limits of + and - polarity are extremely deviating in your case.It's not mentioned in the manual, but you always should use a Null before measuring currents, to achieve highest uncertainty.Same goes for 100mV and 1V ranges; these perform better than specified, if you take care about offsets before mking the real measurement.Another hint: The test report you show here, is this status "As received", or "As Completed"?I have a test report from Keysight, probably Penang, where this 1A range was nOK (i.e. U = Undetermined) before calibration, but good afterwards, although this could only be judged after an ACAL beforehand.

author: chilternview
author_rank: Frequent Contributor
timestamp: January 21, 2025, 11:46:36 am
content: Quote from: srb1954 on January 21, 2025, 09:26:51 amIndeed, the mains filter went on mine back in the summer. Not only a stink but gooey black gunk came out.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 21, 2025, 11:57:39 am
content: for the vfd you could have fine dust on it who could slightly mess with the clarity ...do a full checkout for the famous rifa and other ac input parts who could blow,for the supposedly a3 board drift if your lucky as you say and you dont have it nice catchand you can refer to this thread too for some parts .... sure it goes beyond that lollhttps://www.eevblog.com/forum/metrology/3458a-worklog/

author: aronake
author_rank: Frequent Contributor
timestamp: January 21, 2025, 02:42:34 pm
content: Congratulations!It may not have been running much for the last couple of years since they were calibdated. So keep it running for a couple of weeks (a couple of month better), do recurring ACALs, ideally connect a stable voltage reference and track DC readings and CAL72 values. Best if done in somewhat stable temperature. In case you plan to hand it in at Hatchioji, best to make sure that things have stabilized properly. Some of my 3458a have needed month to get CAL72 to settle in at a low and more constant drift (one almost a year!). And it may be that even its been so long since they were running that the LTZ1000 needed to settle in to. But I never got to measure that.It helps to do above measurements with a python script, which is not too complicated. What seems to be the better and more stabe GPIB adaptor is Keysight/Agilent E5810.I got some VFDs form China. They work very well! And new nice shining VFDs are always nice to look at!As pointed out here previously, depending on your intended usage, there may be better options than a full official keysight calibration.

author: IanJ
author_rank: Unknown
timestamp: January 21, 2025, 02:51:09 pm
content: Quote from: TERRA Operative on January 21, 2025, 09:06:38 amYou are on the right tracks......you've backed up the CalRam and a FRAM conversion is imminent.Once you have had it powered up 24/7 for a few weeks then start logging CAL? 72 in order to evaluate the U180 for any drift. If you come out the otherside of that all-good then you got a real bargain.Attached is a spreadsheet template I created you can use that has the calcs built in.Mine is a 2000 vintage and with a new Keysight front panel, fully FRAM converted.It's overdue a Cal at Keysight which I plan to do in the coming months.I have a 3245A that I fitted a new VFD (Ebay) to and it's perfect......in fact I plan on swapping it with the 3458A VFD as they are identical.Ian.

author: aronake
author_rank: Frequent Contributor
timestamp: January 21, 2025, 03:22:42 pm
content: It may also be an idea to see how CAL72 change after ACAL with temperature differences. Below 0.1 ppm/C is good, above 0.2 ppm/C start to be a bit problematic. Datasheet allow for a bit more though.

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 21, 2025, 05:40:59 pm
content: Thanks all for the info so far, greatly appreciated!I have some good volt and resistance references, but they haven't been characterised to the required extent for this instrument.I have a bunch of vishay resistors, a Fluke 731B, a voltagestandard.com 10V reference, some Yokogawa calibrators, etc, etc, but the best they are adjusted to is my 34461A (The voltagestandard.com reference is on it's original cal).So, a proper 3458A calibration is on the cards to give me a baseline to work from once the dust settles. business expenses etc.Tonight's work was replacing the Rifa capacitors (I'll grab a TDK line filter from Akihavara on Friday, my Shaffner has a date code of 0036, so meh, I'll replace it to be safe), and socketing the NVRAM chips ready for FRAM, and also socketing the U110 EPROM so I could do a firmware upgrade.The firmware upgrade went smoothly, so now I'm on firmware 9.2, so that's nice.I also took a direct dump of the contents of the Cal NVRAM, and it matched perfectly with the data I sucked out the GPIB port using WinGPIB, so happy days (Thanks Ian! Good software!)I've also taken a list of electrolytic capacitors to buy, I'll replace them while I'm inside as they are all over 20 years old now. I'll use United Chemicon KZN etc series where possible for long lifetime.There is a big fat axial cap, 8300uF 35V that might take some searching to find a replacement (Mouser don't have much at the moment) so I'll test that one and see how good it still is.Hopefully the Option 001 RAM chips arrive tomorrow, and they'll go straight in.So far, so good.I also remembered I have a Matsunaga SVC-1010 1kVA (10A @ 100V) autotransformer type line voltage stabiliser. I wonder if it's worth using that to make the line voltage nice and stable during longer data logging periods?Google translated link to SVC-1010 data

author: MiDi
author_rank: Frequent Contributor
timestamp: January 21, 2025, 07:21:41 pm
content: Welcome to the club!At the bottom are all parts listed that should be replaced:https://www.eevblog.com/forum/metrology/3458a-worklog/msg2098195/#msg2098195Quote from: aronake on January 21, 2025, 03:22:42 pmThere are a couple units I know that have around 0.3ppm/°C TC, that is absolutly in spec (0.5ppm/°C TC) and good.Mine has rather high 0.34ppm/°C TC and U180 drift.

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 22, 2025, 05:33:26 am
content: Great, thanks for the list, it helped fill in a few blanks, so now I have a full shopping list on mouser.(Rifa's are done, Line Filter is coming from Akihabara)Here's what I'll buy:Capacitors:Ref DesBrandValuePart No.SeriesA2C702, A2C704Vishay22uF, 63VMAL202138229E3021 ASMA4C7, A4C8Chemi-Con2200uF, 50VEKZN500ELL222ML40SKZNA4C9Chemi-Con15,000uF, 35VEKMQ350VSN153MR35SKMQA4C17Chemi-Con22uF, 50VEKYB800ELL220MF11DKYBA6C1, A6C11Chemi-Con680uF, 63VEKZN630ELL681ML20SKZNA6C8Cornell Dubilier10,000uF, 35V109TTA035MTTAA6C200, A6C201Chemi-Con47uF, 100VEKY-101ETD470MJC5SKYA6C202Chemi-Con330uF, 63VEKZN630ELL331MJ25SKZNA6C203Chemi-Con220uF, 50VEKZN500ELL221MJ16SKZNRifa Capacitors:Ref DesBrandValuePart No.SeriesA6C15, A6C16Kemet2200pF, 350VACR41BF122050T0KR41Option 001:Ref DesPartPart No.A5U123, A5U124, A5U125, A5U12632K x 8 CMOS SRAM62256Misc:Ref DesPartBrandPart No.B1Fanebm-papst612NLEB1ConnectorMolex50-57-9402B1PinsMolex16-02-0104A5U1328K x 8 FRAMInfineonFM16W08-SGA5U121, A5U12232K x 8 FRAMInfineonFM18W08-SGDS1220 to FRAM FM16W08 adapter (PCBWay link)DS1230 to FRAM FW18W08 adapter (PCBWay link)I've also just installed Option 001, which seems to work with no errors. Pic below showing the socketed chips and Opt 001 installed.

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 22, 2025, 09:00:26 am
content: Well, there's the reason I had to put some superglue on the front panel....(And yes, I did put the strap on upside down, meh, will fix it soon when the covers come off again).Time to make a list to sent off to Keysight for a few spare parts.

author: chilternview
author_rank: Frequent Contributor
timestamp: January 22, 2025, 01:42:31 pm
content: I can't recall the exact price Keysight charged for a front panel but it was somewhere in the region of £110 when I ordered it for one of mine a while back.

author: aronake
author_rank: Frequent Contributor
timestamp: January 22, 2025, 01:55:58 pm
content: Quote from: chilternview on January 22, 2025, 01:42:31 pmWhen I contacted Keysight they didn't want to sell one to me, but rather send in the whole multimeter for "repair".

author: IanJ
author_rank: Unknown
timestamp: January 22, 2025, 02:31:02 pm
content: That's what Keysight are doing now.....almost across the board for 3458A parts by all accounts........I must have hit it lucky about 5 or 6 years ago they sold me a new front panel and a front/rear switch.Ian.

author: laichh
author_rank: Regular Contributor
timestamp: January 22, 2025, 02:56:04 pm
content: Hi TERRA Operative,Congratulation & welcome to the Volt-Nut club, $3.5k+ for a used 3458A is really a bargain.Like many had pointed out, there's no specific calibration adjustment to the DCI 1 A range. In fact, all functions & ranges except DCV 10 V, Res 10 kΩ, & ACV, are ACAL corrected. In your case, likely you've got a slightly higher TCR 1 A shunt (R213 on A1 board).If you could get yourself a good 100 mΩ shunt likehttps://www.digikey.com/en/products/detail/vpg-foil-resistors/Y07340R10000F9L/4223414, get it kludges in & you should be good to go.

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 25, 2025, 02:33:53 pm
content: Well, I got a quote from Keysight for a bunch of parts, so I'll sent the purchase order back soon. Seems they might actually sell me the parts directly with some luck.I replaced the line filter in the meantime. The new one was a slightly different size, so a little filing of the plastic on the filter, and a trim of the rear panel sticker (The sticker cutout is smaller than the panel cutout, and it's all installed.No Rifa or Shaffner smoke for me!I also noticed the Pass/Fail output cutout on the rear (visible in the attached photo). Does anyone have any info on that? I haven't found anything so far in my searches.

author: Dr. Frank
author_rank: Super Contributor
timestamp: January 25, 2025, 03:55:28 pm
content: Well, you might be lucky that you're dealing directly with KS in Penang/Malaysia, where the manufacturing and main Engineering support for the 3458A is nowadays located.Volt-nuts here in EU (or as well in U.S.) had to contact either local support, and they request that you send your defect 3458A to them, and would not sell any spare parts anymore since a few years, already.This pass/fail empty connector might be an option, which was never officially available, like opt. 01/02, therefore, might have been a request by electronic manufacturing companies.We use many 3458A in our factory, to precisely measure component values, or calibrate something on the PCBs at those elevated temperatures in the manufacturing halls. (That's the main application of the 3458A, not in a lab in first place). We are steering the 3458A over GPIB, therefore, such a pass/fail is not needed.Anyhow, I can imagine, that other manufacturers would need this function, if they produce something (like components, e.g. resistors), and would like to automate the selection process w/o PC.I had a brief look into the schematics, but could not discover any unused port output on the main CPU board, A5.The Trig In / Trig Out jacks are interfaced to the A/D board A3 via an optical link on A6, outgard power supply.If I remember correctly, the PTB of Germany (or maybe the NIST) used this empty jack for a synchronous 10MHz output signal from A3, via an optical link, to exactly synchronize the high speed sampling for precise AC measurements. You can find several unpopulated component places on the new A3 board (i.e. the very first version of this redesigned PCB), where one could assemble a gate IC, and an optocoupler, to bring the A/D clock (CK10 from U131B) to the outside.FRank

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 26, 2025, 02:02:35 am
content: The delivery guy came with a parcel from Mouser today.So the new fan is installed, and all the electrolytic capacitors are replaced except A4C17 which I forgot to grab from Akihabara last week, so I'll grab that on Monday on my way into work.Nothing else to report so far.

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 28, 2025, 04:26:34 pm
content: Just bit the bullet and ordered a replacement VFD from ebay.Working through the back and forth with Keysight to order parts now too.

author: IanJ
author_rank: Unknown
timestamp: January 28, 2025, 05:53:15 pm
content: Quote from: TERRA Operative on January 28, 2025, 04:26:34 pmHere's my 3245A that I fitted an Ebay VFD to about 2 years ago. Uses the same VFD as the 3458A.My 3458A VFD is still pretty good, no plans to change it out anytime soon (I have an Ebay VFD sitting ready for it though).My HP 3458A (manu. 2000) also sports a new Keysight branded front panel I bought from Keysight UK about 5 years ago.Ian.

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 29, 2025, 05:08:13 pm
content: eeewwwwwwwww.....Something gross happened here. Luckily it washed away with soap and water, so now the binding posts are all clean.I also gave the front panel PCB and the buttons a good clean too.I also found a 2A fuse in the current binding post holder, so that tells a bit of a story about the current range being a bit out....I've stuck a 1A fuse in and once the instrument is all back together and settled over a few days of runtime, I'll give it a self calibration and hope for the best.I can't measure if it will come good or not but it's only a tiny bit out, so a proper adjustment hopefully might bring it good, maybe...I also found the rubber bung where the wires pass through the chassis to the front binding posts was as brittle as Bakelite, so it had to be cut to allow me to remove the binding post assembly, so now I'm on the hunt for something that will fit.The parts manual states it's a "GROMMET-RND 0.5-IN-ID, 0.625-IN-GRV-OD" (12.5mm ID, 15.9mm OD) part for a 1.5mm panel. Shouldn't be toooo hard to find here in metric land I hope... Found grommets from Misumi Vona (A machine parts supplier here in Japan), should arrive Saturday. I also threw in a few plastic GPIB port dust covers too just for fun.

author: aronake
author_rank: Frequent Contributor
timestamp: January 29, 2025, 05:40:40 pm
content: Quote from: TERRA Operative on January 29, 2025, 05:08:13 pmHa! Very Japanese! Important things are clean! How about you bring the 3458a next time you go to onsen? Even for a viking descendant like me, used 3458a can be quite gross before being cleaned up...How cooperative has Keysight been in selling spare parts?

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 29, 2025, 05:46:07 pm
content: Haha, I think the minerals in the onsen water will do the plastics good, come out all smooth and supple.So far Keysight have beenokay..., there is a "procedure" to follow, but I always get my parts pretty smoothly in the end. We'll wait and see how getting 3458A parts go, the purchase order was just faxed today...

author: Kleinstein
author_rank: Super Contributor
timestamp: January 29, 2025, 06:40:02 pm
content: Changing the fuse would not change the accuracy. Cleaning could help with low currents, reducing leakage. Still this would be less an issue with current measurements, but more with voltage and high resistors.The large fuse could have caused damage to the shunts, especially the 100 mA range shunt. The 1 A range shunt would probably still be more robust than a 2 A fuse. Damage to the diode used transistors in the protection would more effect the low current ranges, not the 1 A range.As already written before: there is no extra adjustment for the 1 A range. My best guess for the relatively large deviation at 1A is self heating of the shunt and a relatively high TC of the shunt.

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 29, 2025, 11:35:36 pm
content: I understand that changing the fuse won't affect accuracy, but it does mean a previous user attempted to overload the current input, and maybe even did with the 2A fuse installed...I doubt HP would use a part that has TC characteristics that don't meet their own spec. especially during the calibration procedure. The shunt is rated to 50ppm and is original, no rework evident.All current ranges measure within specification except the -1A range, so I'm concentrating there.I pulled the 1A current shunt out just now and measured it on my 4338B Milliohm meter and it measured at 100.97mOhm, just under 1% tolerance, which is no problem compared to the 10% stated in the parts listing in the CLIP.Also, the +1A range tests ok according to the last cal report, and I doubt the current shunt would work differently in one direction compared to the other....So, the problem seems to be a little deeper. If only I had a way to measure with the required accuracy....... I think I need another 3458A

author: Andreas
author_rank: Super Contributor
timestamp: January 30, 2025, 05:59:28 am
content: What about CR201/CR202 Q207/Q208 in the current input section?Perhaps one of those has a leakage current.

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 30, 2025, 08:02:42 am
content: A1CR201/A1CR202 are both 1N5393 diodes, datasheet says max of 5uA leakage at rated voltage (200VDC), my two have a measured leakage of 0.005uA according to my 34461A, so they seem good.A1Q207/A1Q208 are HP part number 1853-0676, but I can't find a cross reference for them. The CLIP says it's a National Semi part with part number SW5Q011A, but Google says nope to that search term. The Keysight parts finder webpage gives the following specs:Vce - 30VIc - 10ASilicon Transistor TO-220In my unit, they appear to be HP numbered Fairchild parts, with the addition of 'DG22AA' above the HP part number, but Google also says nope to that too.I can pull them out and test, but without a datasheet I can't tell what leakage should be or what to replace them with if needed. At least I can compare the two and see if one has more leakage then the other.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 30, 2025, 12:02:30 pm
content: Leakage at the diodes/transistors could be an issue for very small currents, but should not cause an error for the 1 A range only.Excessive heat can cause a change in the TC of manganin shunts. I still doubt that even 3 A would heat up the 0.1 ohm shunt that much. The danger of overheating would be more with the 1 ohm resistor and thus the 100 mA range.The ACAL step for the 1 A range is different from the other in that it uses a rather small voltage (1 mV from 10 mA test current). So this range would be the most sensitive to offset problems and maybe also the local linearity error at the ADC and amplifier.Before doing more invasive probing I would look how much the cal constant for the 1 A range scatters between ACAL calls and with slight changes in the temperature.

author: laichh
author_rank: Regular Contributor
timestamp: January 30, 2025, 04:54:16 pm
content: Hi TERRA Operative,You may replace the A1 Q207 & Q208 with an ONSEMI 2N6490G or 2N6491G.

author: Rax
author_rank: Super Contributor
timestamp: January 31, 2025, 03:52:09 am
content: Congrats on your going in the realm of the big guns, TERRA Operative! Excellent price, especially in the condition this seems to be in. Awesome find.I have one 8.5 meter (a Prema 6048), but a 3458A is something I've been peeling my eyes out for like there's no tomorrow.Will read your saga with interest.

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 02, 2025, 11:43:10 pm
content: Well, the thick plottens....Upon closer inspection, it seems someone has had a go at repairing the A1 board before...There is flux residue and slightly 'different' chips in some positions. Correct types but the marking font looks a little different.All up I see the following chips have been replaced: A1U1, A1U2, A1U6, A1U9, A1U17, A1U106, A1U201, A1U202, A1U203.I suspect someone shotgun replaced these chips hoping to land on the bad one. As the instrument is only a teeny-tiny bit out on the -1A range it seems they got pretty close!Although these chips aren't in the measurement path, so either it wasn't switching ranges due to 'the fault', or there are/needs to be more replacements that I have to track down.Cal results as purchased are a follows:TestConditionsMinimumMeasuredMaximumRangeInput1A-1A-1.000192A-0.999910A-0.999938A

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 03, 2025, 12:18:58 am
content: Highlighted in red are the replaced chips.

author: picburner
author_rank: Frequent Contributor
timestamp: February 03, 2025, 04:53:45 am
content: U203 appears to have been soldered from above without disassembling the A1 board.

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 03, 2025, 05:25:03 am
content: They all appear the same way.I think next I'll test Q207 and Q208 for leakage. The replaced IC's are unlikely to be the problem as they are in the switching side of things and that all seems to work.I might also give the board a gentle bath in isopropyl alcohol to remove flux residue for good measure too.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 03, 2025, 11:11:58 am
content: Most of the "replaced" chips seem to be 4094 shift registers. This are digital chips for the control and would not cause a minor error. If they were bad they would cause a much more drastic error. Similar flux at these chips would not be an issue as this are digital signals.A test one could do (with the meter assembled) is checking the stability of the 10 ohm resistance range. This would requite a really good resistor in the 10 ohm range. The question is if the 10 mA test current drift with time, especially from self heating of R307.A possible issue for the ACAL part could be too high a TC for R307 in the 10 mA current source. 10 mA at 300 ohms is quite some power. This could lead to an additional error in the ACAL part for the 100 mA and 1 A ranges, that could add up to the 1 A range.Another point to check could be the input bias current (e.g. in Volt mode). Too much bias from the amplifier could effect the current readings too, as the signal still goes through relatively large shunts.

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 03, 2025, 03:06:52 pm
content: I pulled and tested Q207 and Q208 with my Peak Atlas DCA75 Pro, and according to that, all parameters are nominal and quite well matched between the two, and leakage is 0.000mAQ207:Hfe = 161 @ Ic = 5mAVbe = 0.617V, Ib = 1mAVbe = 0.664V, Ib = 5mAVce sat = 0.006V @ Ic = 5mA, Ib = 1mAIc leak = 0.000mAQ208:Hfe = 162 @ Ic = 5mAVbe = 0.598V, Ib = 1mAVbe = 0.648V, Ib = 5mAVce sat = 0.008V @ Ic = 5mA, Ib = 1mAIc leak = 0.000mAAs part of removing and testing them, I pulled A1 board and great googly moogly there was a nice amount of flux here and there on the back of a board that should be clean.... Including inside and crossing a number of guarded areas.It's obvious that whoever did the previous repairs, while their soldering skills were good, didn't bother to clean up any of their work. There were even solder splashes all over the place too (none shorting anything thankfully). The tech probably used a spring-loaded plunger type solder sucker...So, the board got a good isopropyl alcohol bath and is now all squeaky clean.I also got a new rubber bushing to replace the brittle one where the front panel input wires pass through the chassis, so that's now installed too.

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 07, 2025, 07:10:59 am
content: Mmmmmmmmmmmm. Spare parts.... <drool>Depending on how my existing Agilent branded display window looks in the new front panel, I might see if they still have new Agilent ones available for my next parts order.The other option is to just go to Keysight branding, but that somehow feels less 'pure'....

author: aronake
author_rank: Frequent Contributor
timestamp: February 07, 2025, 08:15:09 am
content: Quote from: TERRA Operative on February 07, 2025, 07:10:59 amNice! How much did you pay for the different parts if its ok to ask that?

author: faraday
author_rank: Regular Contributor
timestamp: February 07, 2025, 09:40:03 am
content: Quote from: TERRA Operative on February 07, 2025, 07:10:59 amjealousDo you have source for diaplay panel my ?

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 07, 2025, 02:37:51 pm
content: After 4 pints of good German beer, lets see if I can do this....Prices are subject to exchange rates and account discounts etc, so may vary...All prices in Yen because I'm in Japan.Part no.DescriptionPrice eachPieces03458-40215Key cap, grey, serial number 2823A21100 and above¥1136203458-40214Key cap, white, serial number 2823A21100 and above¥1515103458-40212Front Panel Sub Assembly¥28,41215041-9176Trim strip - FM, Front, Frame-Top¥2,83615041-9170Trim-FR FR Side 1 each¥1,13625041-9186Cap - Strap Handle Retainer - Front¥2,65225041-9187Strap Handle Retainer - Rear¥2,65220515-1132Screw-Machine POZI M5X0.8 10mm-LG SST-300 Passivated¥4704The photos include two extra bits for an E4419B RF Meter, which are not included above.Not great, not terrible. It all adds up quick, but my instrument will be like new, so all good considering the ¥100,000 discount I got when I bought it.

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 07, 2025, 02:41:20 pm
content: Quote from: faraday on February 07, 2025, 09:40:03 amI just bought it from eBay as it was the cheapest, but they are available on eBay and Aliexpress.I'll soon see if it is a good one when it arrives in a few weeks or so. It was listed as 'new' so I suspect it is a 'ghost shift' part, like the 53132A etc VFD's I have bought previously which worked perfectly.

author: factory
author_rank: Super Contributor
timestamp: February 07, 2025, 08:01:27 pm
content: Quote from: TERRA Operative on February 07, 2025, 07:10:59 amDo they have HP branded panels available? It just feels wrong to have anything else on the front.David

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 08, 2025, 03:51:48 am
content: I'll ask. My unit is only half bastardized as an Agilent.... (Thanks Carly....)

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 08, 2025, 04:44:49 am
content: I picked up a 34330A current shunt this week, to allow me to measure up to 30 Amps.I gave it a quick test on my 34461A multimeter and with 1A input from my Siglent PSU, I get 0.99829AWith the same current straight into my 34461A multimeter on the 3A range I get 0.99826AA difference of 0.003%, and it's specified at 0.3%So, it seems well within spec.

author: factory
author_rank: Super Contributor
timestamp: February 08, 2025, 12:04:01 pm
content: Quote from: TERRA Operative on February 08, 2025, 03:51:48 amThanks, I'm probably never going to acquire anything other than the 34401, from the range of more modern HP DMMs, but it would still be interesting to know.David

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 09, 2025, 07:04:39 am
content: New front panel and VFD is all installed, and looking resplendent.Next job is to finish the FRAM/NVRAM replacement once Digikey delivers a couple parts next week.I sent an email to Keysight about the HP/Agilent branded display window, so let's see what they say (I suspect only Keysight branded ones will be available though).

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 10, 2025, 06:50:10 am
content: And now I have FRAM installed.My T48 programmer apparently doesn't like these adapters, from searching around the forums it seems the DS1220-FRAM adapter board needs a programmer-adapter to make the chip look like the original FRAM part FM16W08 to the programmer. The DS1220-FRAM adapter reduces the capacity of the 8K x 8 FRAM FW16W08 to the 2K x 8 of the DS1220, so the programmer-adapter apparently works fine as long as you don't try to address more than 16K.I ordered some programmer-adapter PCB's to play with, but in the mean time I just programmed the new FRAM directly before soldering it and ignored the programmer error messages due to the different capacity of the DS1220.On installing it into the 3458A, it works perfectly, and extracting the data via GPIB using WinGPIB produces an exact match to the data I extracted earlier from the original DS1220, so win.Once the programmer-adapter boards come, I'll play with them to see how it works.Credit to IanJ for the original design of the programmer-adapter -https://www.ianjohnston.com/index.php/videos/160-video-blog-132-3458aAs for the other two FRAM, I could never get a good verification after write, except once for some weird reason, probably due to copying from one chip type to another or user error?In the end, I realised I didn't care one bit about any previous saved user data, so I blanked both the two FRAM's, stuck them in and let the 3458A initialise them. After powering on to let the 3458A tell me what I already knew and to do its thing with the RAM, then another reboot, and I had no errors at all.The 3458A passes all extended self tests and is working perfectly.Now that the instrument is all polished up and restored to my satisfaction, time to figure out how to figure out what's up with that -1A range....Once I have received the FRAM programmer-adapter and made sure it works, I'll release all my PCB design files in this thread for others to use.

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 11, 2025, 04:44:13 pm
content: Been thinking about how to figure out how to figure out this problem on the -1A range...Has anyone worked out how to convert the calibration data from the NVRAM to a list of (I assume) gain and offset numbers?I have seen this done with other HP multimeters..I was thinking of decoding the cal data I have now, then running an ACAL, dumping the new cal constants, decoding, and seeing if there are any changes now that I cleaned the A1 board that would correct for the out-of-bounds -1A range.Anyone think that might be worthwhile to try?

author: Echo88
author_rank: Frequent Contributor
timestamp: February 11, 2025, 05:25:30 pm
content: The cal constants can be queried by using the CAL? function, if thats what youre after:https://xdevs.com/doc/HP_Agilent_Keysight/3458A/03458-90017_Ed6.pdfpage 65

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 11, 2025, 05:31:07 pm
content: Nice. I'll whip up a Python script to pull the data out in the next few days.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 11, 2025, 05:48:48 pm
content: I don't think cleaning would have changed much with the 1 A range. If effecting the 40 K ref. resistor it could have an effect on all current ranges. Soldering the shunt can however ahve changed the value a little and this gets corrected. So one could get a slightly different number.It could make sense to run ACAL at a few different temperatures and compare the CAL constants, especially No 100 for the 1 A range DC gain. This could give a hint on the TC of the shunt in the tested range (this can be different from the parts specs, that are usually upper limits for a quite large range).A point can also be just look how much the cal constant scatter between repeated ACAL runs. This gives an idea on how much is from more random parts.p.s. Another point with testing is a crude test on the hard INL. For this one could use something like an RC combination (e.g. 1000 µF and 10M) to cause a slowly changing voltage and than record data on the decay of the voltage. After subtracting a smooth fitted curve one gets an idea on the hard INL part. For the 1 PLC case some errors are larger than in the 10 / 100 PLC case. So while simple the test could be quite sensitive. This would especially see errors in the small slopes of the ADC. The ACAL procedure depends on the good linearity of the ADC - so an INL issue could cause an ACAL problem.

author: Dr. Frank
author_rank: Super Contributor
timestamp: February 12, 2025, 11:55:10 am
content: Quote from: TERRA Operative on February 11, 2025, 04:44:13 pmHello,I guess you never took notice of my thoughts and ideas on this topic:https://www.eevblog.com/forum/metrology/agilent-3458a-i-joined-the-club/msg5790203/#msg5790203I am meanwhile in doubt that your 3458A really has a problem, or you should find a method to test that range Independently.So again my questions:1. This initial deviation of the 1A range, was it on the "As received", or "As completed" part of the test report?(Please publish the complete report, so that we can as well check)2. Do you have the possibility to make an independent precision check?3. Have you taken offset readings into consideration?What is the zero reading in the 1A range?Do you observe an excessive Null reading?4. What does the test report state about the 1A AC range?5. Have you seen any modifications on the A1 board, concerning the different shunts, or the switches?Frank

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 12, 2025, 12:28:55 pm
content: Apologies, I didn't mean to ignore you, I was just so caught up getting my fingers dirty inside this unit....I've attached the most recent, and only, cal report I can get my hands on. That should show what's going on.My only other meters to do precision testing with are a 2-year out of cal 34461A, and two 3478A's which are weeelll out of cal date, but all three seem to be reading pretty good (but not exactly the same as each other as is expected).I have various calibrators and power supplied, but my Fluke 332D and 335A both are waiting their turn on the healing bench..I have some unplated copper short PCB's on the way from PCBWay, so will be able to properly check zero readings soon.No mods on A1 board specifically for shunts or switches/relays etc (Mostly on the logic), but some other things had flux residue, so maybe removed and reinstalled for testing. I don't know which ones exactly though

author: Dr. Frank
author_rank: Super Contributor
timestamp: February 12, 2025, 08:33:43 pm
content: Quote from: TERRA Operative on February 12, 2025, 12:28:55 pmYou don't need any short for zero checking the current ranges.Just let the 3458A warm up, then make an ACAL OHM, select range 1A DCI and check the zero reading.The internal 0.1 Ohm is 'short' enough.If you have a stable 100mA .. 1A DC constant current source, you might then apply this current in either polarity, to check for any asymmetry.The FLUKE 5730 reverses the current by its own, so that possible problems are hidden.It's strange, that all DCI ranges apart from 1A are symmetric, as well the Min / Max limits, and the 3458A is practically reading exactly in the middle between Min / Max.That's evidently different for the 1A range, where the Min/Mx limits, given by the 5730, are extremely asymmetric, and the 3458A reads quite low.My guess is, that they had a problem with the 5730A in first place.Secondary option is, that the shunt has a very high internal Offset, although these offsets probably are compensated by the ACAL.TiN had some undisclosed problems with offsets, when he replaced the shunts with better ones. There seem to be some offset managing magic, when you study the schematics. There are a bunch of strange bridges in series, 4 or five, and i never understood their purpose.So, please just check the zero reading first, to rule out any strange e.m.f. problems around the 0.1 Ohm shunt.There is a zero DCI reading test, and that looks good ..Concerning prior nulling of critical modes and ranges, HP as well as other DMM makers haven't put much attention to this problem.All DC modes, where the 100mV range is used internally, i.e. 100mV DCV, 100V DCV, and DCI ranges 100mA and 1A, a prior nulling might improve the uncertainty by an order of magnitude. These internal offsets / e.m.f.s strongly vary, or might not be properly taken into account following the ACAL procedures.. You can easily see that, if you put a short on the Input jacks, select 100V DCV range, and then check the zero reading.. you will probably see several 100µV of offset, or several ppm of reading error, which could easily be compensated beforehand.Frank

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 13, 2025, 08:46:26 am
content: I wrote a quick and dirty script in Python to copy out all the cal constants (I plan to expand on it to do more Cal functions as I get the energy..)Attached is the script, and the Excel spreadsheet of my before and after ACAL results.On a side note, libreoffice calc has some issues with rounding etc, I'm not getting 1+1=2, more like 1+1=1.999999999999 (not those exact numbers, it trips up with a lot of digits after the decimal point), which is great..The zero reading on my 1ADC range is hovering around +0.0000007 ADC at 100PLC after settling for a while. Script now on Github here:https://www.eevblog.com/forum/metrology/agilent-3458a-i-joined-the-club/msg5822175/#msg5822175

author: laichh
author_rank: Regular Contributor
timestamp: February 13, 2025, 09:39:53 am
content: Quote from: TERRA Operative on February 13, 2025, 08:46:26 amHi TERRA Operative,You could get a better sense of drift between ACAL by comparing the ACAL constant in the following way:- Offset (zero) constant in ppm of range- Gain constant in ppm changes between ACAL

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 14, 2025, 01:21:58 am
content: Quote from: factory on February 07, 2025, 08:01:27 pmThe official word from Keysight is they only have Keysight branded display windows, no HP or Agilent left.So either that's true or we need a Keysight insider to raid the warehouse to pilfer parts for us that are being hoarded for big corporate customers.I ordered a Keysight display window. I feel a little dirty, but the window will be shiny....

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 14, 2025, 01:28:14 am
content: On another note, I found that part 1460-1311 in my instrument is broken.It's a little be-cu leaf spring attached to the chassis on the inner left side that contacts a gold pad on the front panel PCB for shielding/grounding purposes.And of course that tiny little part is non-orderable.....So I am currently conducting negotiations with Keysight service department to try to get my hands on onewithoutsending my instrument in under the promise of a future calibration, only for them to charge me an arm and a leg to tighten one little screw...I think I already know the answer, but here's hoping.........

author: Zoli
author_rank: Frequent Contributor
timestamp: February 14, 2025, 07:12:53 am
content: Quote from: TERRA Operative on February 14, 2025, 01:28:14 amI have something similar:https://techetch.com/products/fingerstock-gaskets/I hope is good start to find third party replacement; good luck!!!

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 14, 2025, 07:19:06 am
content: Yeah, I'll have to either make something from Be-Cu stock and harden and plate it myself, or figure something else out.I might buy some 0.25mm beryllium copper sheet from ebay and have a play with making my own. Can't be toooo hard...Keysight replied today with a hard nope on supplying that part, the service rep didn't even offer any possible alternative, just pretty much corporate speak for 'Nope not available for purchase, I hope we can sell you something else soon'.....It seems I will have to send it in to get that one shitty little bit of metal if I want the proper part from Keysight.....

author: aronake
author_rank: Frequent Contributor
timestamp: February 14, 2025, 08:06:08 am
content: Quote from: TERRA Operative on February 14, 2025, 07:19:06 amWill be interesting to see how that goes. It would not surprise me if that comes with a full standard repair package, calibration and a 3000 USD price tag...Have you tried any service note 18 a.k.a. drifty A3 test yet?It may also be of interest to test temperature coefficient of the meter. Both without Acal (typically this show TC of the A3 board) and with Acal (typically this show TC of voltage reference).

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 16, 2025, 12:32:59 pm
content: I have some numbers according to the service note, but I'm running the test now. I have had the 3458A on for 3 days so far, so next weekend I'll give it a test.According to the original Cal value 72, and what I have now after 3 days (and calculating for 3 days rather than the who knows how long since last ACAL), I'm getting -0.108ppm per day, so it looks ok so far...My serial number is a bit earlier than what is noted in the service note, so hopefully I've missed out on the fault, or hopefully it was corrected during one of the two calibrations that have been done that I know of...Time will tell.

author: aronake
author_rank: Frequent Contributor
timestamp: February 16, 2025, 01:03:53 pm
content: I have some 1990ies 3458a that have had the A3 replaced, so suspect that was case of drift. And other have reported other older 3458a with drifty A3. And seems there have been cases of drifty A3 well after the service note was issues.If you see some indications of -0.108ppm per day now that looks very promising. And even if your first tests show some drift, letting it run for some time may help. I have a 3458a that had a drift of -0.4 ppm per day. Let it run and monitored CAL72. Then after around half a year, it decided it had enough of drifting and leveled out at around -0.03 ppm / day and have been there for the last 2 years.

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 16, 2025, 01:06:08 pm
content: I have it sitting in my rack now, so I'll just keep monitoring it and record a reading once a week or so and see how it goes.

author: srb1954
author_rank: Super Contributor
timestamp: February 16, 2025, 09:16:28 pm
content: Quote from: TERRA Operative on February 16, 2025, 12:32:59 pmThe A3 drift issue exists for a wider range of serial numbers than indicated in SN18A. My unit was a 2005 build and its serial was after the range specified in SN18A but it still had severe drift and required replacement of the A3 board.If your unit was calibrated/serviced by HP/Agilent/Keysight you might be able to enter the serial number into the support site and get a history of work done on your unit and/or any recommended remedial work required.

author: aronake
author_rank: Frequent Contributor
timestamp: February 17, 2025, 05:45:19 am
content: Quote from: srb1954 on February 16, 2025, 09:16:28 pmWhere can this be done?

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 17, 2025, 05:53:22 am
content: https://support.keysight.com/s/service-and-warranty-status?Or ask Keysight directly, and hope and pray they will actually give you something if you don't have a registered business......

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 17, 2025, 02:11:26 pm
content: A batch of shorting links arrived today!They are bare copper and edge plated, and work quite well.I have a bunch, so if anyone needs some, I can send some out for a couple dollars each plus post (just in an envelope so will be cheap from Japan to worldwide I expect).

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 18, 2025, 07:03:02 am
content: I've uploaded my calibration values downloader script to Github.Feel free to improve it or whatever..https://github.com/JaredCabot/3458A-Calibration-Downloader/

author: faraday
author_rank: Regular Contributor
timestamp: February 18, 2025, 10:50:32 am
content: Quote from: TERRA Operative on February 18, 2025, 07:03:02 amIs little typo, isn't ? 3457a

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 18, 2025, 10:54:21 am
content: Whoops! That'll teach me for working at 2AM.....Fixed!https://github.com/JaredCabot/3458A-Calibration-Downloader

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 28, 2025, 01:21:36 pm
content: I swear I'll do it! I'm not kidding, I'll totally do it and I'll be glad, you hear? GLAD!

author: Grandchuck
author_rank: Super Contributor
timestamp: February 28, 2025, 01:53:36 pm
content: Will you then paint it black?

author: aronake
author_rank: Frequent Contributor
timestamp: February 28, 2025, 02:30:24 pm
content: Quote from: TERRA Operative on February 28, 2025, 01:21:36 pmIs the Agilent panel badly scratched? Generally I think the Agilent panels looks better, and the genuine time correct choice. And i wonder who put 1/2 at the bottom of the keysight panel.......

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 28, 2025, 03:32:34 pm
content: I tried to get a replacement Agilent display window, but none available...The Agilent one is a bit scratched. I'm almost thinking of making a stencil (I have a sticker cutter) so I can polish the Agilent window and repaint the writing and logo with a stencil, maybe.re. painting it black.... Even I have limits to my madness...

author: Dr. Frank
author_rank: Super Contributor
timestamp: February 28, 2025, 04:10:08 pm
content: Quote from: TERRA Operative on February 28, 2025, 03:32:34 pmI'm so glad, that my unit from 2000 still got this HP logo on the display filter, even though it had some scratches across.I just used plastic polish to get rid of all but one faint scratch .. I would have felt uncomfortable to have such a legendary DMM with agilent or keysight on it.Well, the VFD of my unit shows signs of use, but I still have no visual problem with that, as I really USE it when making automated measurements.For me, it's not a museum artefact, but a tool.Frank

author: IanJ
author_rank: Unknown
timestamp: February 28, 2025, 05:37:37 pm
content: I just looked out my old "HP" front panel and it's certainly got a few dings, bangs and chunks out of it......however, the HP window is pretty nice and I am sure it would polish up.......so maybe I'll replace the Keysight window that came with the new Keysight front panel I had fitted back in 2018.To me, it's just a personal decision on whether to stick with an old battered front panel or have a brand new one. I prefer pristine test gear hence why I changed mine........but I do think, a nod to the original 2000 heritage of my 3458A is probably worth doing.Now where did I put that perspex polish.........Ian.

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 28, 2025, 06:28:48 pm
content: Well, I did it. I stuck the Keysight display window in.More shiny!I also made a leaf spring (Part number 1460-1311) for the grounding of the front panel.As previously mentioned, it's a non-purchasable part, so I had no choice but to make my own...The parts manual says it's a Be-Cu leaf spring and I measured the remaining bit at 0.25mm thick, so I bought some 0.25mm thick Beryllium Copper sheet from Aliexpress and cut a chunk out, drilled the holes and tinned it with the soldering iron.I contemplated nickel plating it, but that was all a bit too hard. Solder is fine. When this goes in for calibration, I'll try to convince them to replace it with the real part then.I'll install it Sunday night, once the timer for one week continuous operation has elapsed as specified in the drift calculation in service note 18A, so I don't ruin the test.Then I can compare ACAL constants to check for the common drift issue, at least for the 1 week test. Longer testing will follow once it's installed back in my rack.

author: Dr. Frank
author_rank: Super Contributor
timestamp: February 28, 2025, 09:00:50 pm
content: Quote from: TERRA Operative on February 28, 2025, 06:28:48 pmCongrats, and have fun!As Ian is currently in the thread, let me ask again, whether your 18A drift measurements of U180 (by means of Ians program) take its temperature coefficient into account, i.e. compensate for this effect?I guess, I'll append my latest measurements for comparison. The U180 drift nearly vanished over the past few years.FrankI always monitor CAL? 72 (DCV gain) and CAL? 175 (ACAL DCV temperature).The first diagram then calculates the T.C. of U180, which fits to the 3 T-points taken during warm-up.The T.C. was later confirmed by separate T.C. measurements of the overall T.C. minus the T.C. of the LTZ1000A reference.When I plot the U180 gain constant over time, and substract the T.C. influence, I get a seemingly consistent, temperature-compensated drift curve for U180.In 2019, I made the latest 10V DC calibration, which automatically gives a small jump of CAL? 72.The drift was already very small, 0.5ppm/y or 0.002ppm/d and practically vanished for the last 2 years.

author: IanJ
author_rank: Unknown
timestamp: March 01, 2025, 10:00:31 pm
content: HP window fitted on my 3458A today…….I feel better!Ian

author: TERRA Operative
author_rank: Super Contributor
timestamp: March 02, 2025, 02:39:35 pm
content: And to provide balance in the cosmos, mine now has a Keysight window. Ying and Yang.Tonight marks the end of 1 week constant power on my 3458A to check for A3 drift as per Service note 18.The service note gives a maximum value of >0.43ppm per day, and once I plug my values into the formula, I get a daily drift of -0.0189ppm, so I think I'm good.I also installed my little leaf spring too, so that's all good now and the instrument has been returned to the rack to be left running 24/7. (I use the DISP 2 command from the front panel to blank the display when not in use. I also set NPLC to 200 to reduce wear on the SMPL annunciator as well).So all is happy for now. Next step is to try to figure out how to figure out what is up (if anything) with that -1A range from earlier.I need to figure out how to measure that with only one 3458A. Or just bite the bullet, get a cal done and hope it is good....Also, I uploaded a video to youtube on replacing the NVRAM's, I think I got the details correct......https://youtu.be/uNbI3SUZ7oI

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 02, 2025, 03:01:04 pm
content: There is a special GPIB command which turns the display off completely.Somewhere in the Metrology folder I have described how to use the proper command syntax. Maybe it's one of the additional BASIC commands, then it might be used with the function keysSuch a command you could find on many instruments, when complete darkness is required for optical experiments in the lab.FrankGot it:https://www.eevblog.com/forum/metrology/repair-old-rusty-hp-3458a/msg800134/#msg800134Problem with that command is to properly define the correct quote marks in your specific programming language

author: drhex
author_rank: Regular Contributor
timestamp: March 03, 2025, 11:36:30 am
content: Mine also got a Keysight window, ditched the original HP as it was beyond polishing. Whole front did look like it had been in the dump already. Using @ianj's spreadsheet, I arrived at 0.03155 average drift, given I am in a totally temperature uncontrolled environment I consider this an excellent result. Figuring out TC would be an interesting one actually.

author: TERRA Operative
author_rank: Super Contributor
timestamp: April 19, 2025, 11:53:39 am
content: Well, after a continuous run over the last 60 days since last ACAL, I get a drift value on cal constant 72 of 0.0004ppm per day.0.4ppb/d isn't too bad I guess.I'll have to set up temperature logging and start logging data points more frequently to see how it drifts up and down over time.

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 19, 2025, 12:22:08 pm
content: Quote from: TERRA Operative on April 19, 2025, 11:53:39 amWhich drift are you referring to?The U180 will not drift , but the volt and resistance references inside might drift over time.. which can be monitored by external references, and which do not drift in my instrument (from 2001) at all.i do not leave my 3458A running all the time, only when in use, and I lowered the oven temperature to about 65°C, from 95°C.Therefore, the LTZ chip does not drift any more.Frank

author: TERRA Operative
author_rank: Super Contributor
timestamp: April 19, 2025, 01:33:20 pm
content: I'm talking about the Service Note 18A, testing for drift of the A3 assembly.

author: aronake
author_rank: Frequent Contributor
timestamp: April 19, 2025, 02:34:24 pm
content: Don't you think its time for your 3458a to get a brother? Then they can help track each others PPMs.Here is an interesting grab as you live in Japan. May just be to change the user data and calibration rams to get it working properly.And congrats on the A3 stability on the one you bought.https://auctions.yahoo.co.jp/jp/auction/k1173946045It is allways a bit of A3 stability gambling to get an used 3458a though.

author: TERRA Operative
author_rank: Super Contributor
timestamp: April 19, 2025, 02:38:04 pm
content: I wish I could buy a second meter....But I just bought an Advantest R6161 that set me back a bit, so I have to keep selling off unused equipment to make space and more funds.

author: aronake
author_rank: Frequent Contributor
timestamp: April 19, 2025, 03:01:32 pm
content: Quote from: TERRA Operative on April 19, 2025, 02:38:04 pmI have one too. With a bit of tweaking of the current of the zener reference, and insulting the zener reference a bit more, i have gotten it pretty stable and pretty low noice for postive voltages. For negative voltages is show for some reason I dont know quite a bit more noise. Ideally I would want to swap the zener for a LTZ1000 circuit, but as the zener is built to sink current in a way a typical LTZ1000 circuit cant handle, I have not came any further on that.

author: TERRA Operative
author_rank: Super Contributor
timestamp: April 19, 2025, 03:06:07 pm
content: You don't happen to have any schematics or service manuals etc for the R6161 do you?I have the English operation manual, but Advantest were generally not very forthcoming with schematics and in-depth service info..

author: aronake
author_rank: Frequent Contributor
timestamp: April 20, 2025, 04:50:30 am
content: Quote from: TERRA Operative on April 19, 2025, 03:06:07 pmUnfortunately not. Only what you have.

author: guenthert
author_rank: Frequent Contributor
timestamp: April 21, 2025, 09:55:00 am
content: Quote from: aronake on April 19, 2025, 02:34:24 pmJust out of curiosity (I don't have the means to join the club and fortunately no need either), how bad is the A3 drift, when it drifts? I understand that such an instrument won't match (or rather cannot be calibrated to match) its stated specifications and won't be of much use as a voltage/resistance/current meter, but will it measurably affect its use as ratio meter? I think it was@almwho mentioned that he uses his meters only as ratio meters anyway. If one is interested only in DCV or DCI and resistance and has good (stable, calibrated) standards available, then a 3458a with a drifty A3 would still be of value, wouldn't it?

author: TERRA Operative
author_rank: Super Contributor
timestamp: April 21, 2025, 10:00:11 am
content: The magic number is 0.43ppm drift per day.If you exceed that, your instrument is out of spec and needs a new A3 board.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 21, 2025, 10:26:28 am
content: Quote from: guenthert on April 21, 2025, 09:55:00 amHP gave the limit of 0.43 ppm per days, but they should probably better give it as 3 ppm over a week. For a reliable value one would usually want a week or more (if the temperature is not that stable). Usually good meters have way less drift, like < 1 ppm/week and bad units tend to get way worse, like > 10 ppm per week.A 3458 with a drifty A3 is not really usuably, at least not seriously: the calibration is no longer valid and expect errors.The drift test checks the ADC gain. No need for an external reference to correct that direct effect. The simple ACAL call would correct for the ADC gain drift - this way the dirft is also measured. However ACAL can not correct for other errors (e.g. linearity - up to the point of causing an error message) that usually come with the defect. The gain drift is only the error that is relatively easy to detect with no extra hardware.Ideally HP/KS should add a check of the gain drift as part of ACAL - they could keep a few older ACAL values and see major drift. No sure of the meter contains a real time clock though, but many meters run 24/7 anyway.

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 01, 2025, 04:40:41 pm
content: So after keeping an eye out for a while, I finally bagged a Yokogawa 2792 series 10 Kohm standard resistor (part number 279208).The seller was selling it as outside specification, but I thought there was a chance that it was a matter of the seller not measuring it properly.When it arrived, it was actually reading a little high, at 10.00111 Kohm (0.0111% high of a rated 0.001%) but I assumed that was just due to age, or something.I opened it up and was cleaning the teflon standoffs inside as they had some gunk from the oil coating the interior and then found that it was now completely open circuit after reassembly!After carefully inspecting the resistance wire, I found a break at the point the resistance wire was soldered to a bit of thicker copper wire that was then soldered to the teflon standoff!I think this must have been about to break before I poked my fat fingers at it, hence the slightly higher reading.I think some of the gunk (which was green...) may have been a little corrosion there...After I soldered it back together, now it reads realllly good.Today I ran my aircon in my room down to 20 degrees C as that is the temperature that the resistor is rated for, then let it all settle for half a day and ran an ACAL on the 3458A at the 20 degrees.The attached picture is the result. Absolutely 100% spot-on!Now, the big question that remains is: Are both of these things coincidentally drifted in the same direction? Or are they both spot on at 10K ohms?I now need to source some mineral oil to fill the resistor for insulation and thermal mass, and start collecting more of these resistors to complete the set (They range from 0.001ohm to 1Meg, and apparently there is a rare 10Meg type too)

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 02, 2025, 07:58:54 am
content: And now I actually set the range correctly to get the extra digit at the end, and still a zero!

author: aronake
author_rank: Frequent Contributor
timestamp: June 02, 2025, 09:41:00 am
content: I would see the exact match more as a positive sign, and quite a bit of coincidence rather than some particularly strong proof of both being quite exactly 10K ohm. The old version of Yokogawa 2792 have quite a bit of TC except for their peak on the TC curve which seems to be in a 5 degree range or so. The 3458a is also not great when it comes to TC and resistance.Still very good they show the same, and very good you managed to fix the 2972.

author: iMo
author_rank: Super Contributor
timestamp: July 29, 2025, 08:01:29 am
content: IMSAI guy has started with his repair..

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 11, 2025, 01:19:20 am
content: So, on a whim I just performed another A3 drift test, after 265 days of continuous power-on.I get a drift of -0.0111ppm.I'm calling this 3458A as good.

author: Rax
author_rank: Super Contributor
timestamp: September 11, 2025, 01:32:24 am
content: Quote from: TERRA Operative on September 11, 2025, 01:19:20 amYeah! I think that's nominally dead on.