HP 3458A ; A/D board spare part availibilty and cost - Page 1
Forum section: electronics / general

author: voltampere
author_rank: Regular Contributor
timestamp: February 16, 2020, 10:38:51 pm
content: Dear voltnuts,i aquired a HP3458A fromm ebay in decent optical condition.According to the date codes on the ic's it should be from 1989.The A9 reference seems to be stable but i suspect the A3 PCB ( A/D board ) to be drifting seriously.The drift is very random and unpredictable.Sometimes it will not drift for about 12 hours. Sometimes it is running away 3 to 5 ppm in 12 hours.It will always come back within 0,2 ppm after an ACAL DC.I got in contact with Keysight Germany to get an idea how much a replacement A3 board would be.First problem was finding the right part number. The part that is inside my unit seems to be the first edition.The part number is 03458-66503. In the keysight part database you will get 03458-66513 as the replacement part number for it because the 66503 is obsolete now. But findapart@keysight.com emailed me that this part is"NFTS" meaning not for trade sale and that i should contact tech support at keysight germany for a repair of the HP3458.I asked KS germany to quote for the 03458-66513 and the first reply was that they only have a few of these boards and they will not sell the spare parts but i can send the unit and they will replace the board. Material + labour = 2.000 € ( + VAT ).I talked to some KS support guys on the phone and asked which part they would use to repair a new HP3458A ( RoHS version ).They were unsure if that part would be compatible and said to contact me when they found out.I read a post here where somebody confirmed that the new version of the A3 board ( part 03458-66523 ) would definitely work in older units ( fully backward compatible). So asked them if they would sell the 66523 spare to me.Got an email two days later where they told me that they usually dont sell the new version either but would make an exemption and quoted 2.000€ ( + VAT ) for the board only!!!That is just a bit too much i think.Now my questions.Does anybody have any experience about getting an A3 spare board ( tested, no second hand ).Should i try to get it from another support center , UK for example?Are the old version ( 66513 ) boards really that rare already?I dont think i want to spend that much many for the spare board.How are the chances to get my drifty boar cured?I had the ( crazy ? ) idea to put the board in the oven at 60 degrees celsius for some hours to get the humidity out that might be the cause of the drift.Would it cause more harm than help?Hoping to get some ideas from the HP3458 repair experts...( TIN ?!!! hello...)Thanks to all for any input on thisBest regardsjoerg

author: TheSteve
author_rank: Unknown
timestamp: February 16, 2020, 11:11:58 pm
content: Your only choice is to buy a refurb board from Keysight as far as I know. They tend to have unknown drift/noise, some are certainly better then others.If you can't find anything else and do really need one I have a refurb that has been tested for noise and drift I can sell.

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: February 16, 2020, 11:58:28 pm
content: Voltampere, your drift problem sounds suspiciously like a bad solder joint or cracked PCB trace, you might take a very close up look at your board and see if you can spot anything before popping for a replacement board.

author: TiN
author_rank: Super Contributor
timestamp: February 17, 2020, 05:12:26 am
content: Graphs. This thread is pointless without graphs. I'd also wouldn't have any conclusion about ADC stability untill you ran the unit for a month, non-stop, to rule out storage/settling issues.There are also more than two A3 versions, but even cheaper refub one would set you back $900+ USD if you are in US. Since you are in Germany, add extra and transform currency to EUR. So 1500 EUR+ is what I would expect as reasonable.

author: voltampere
author_rank: Regular Contributor
timestamp: February 17, 2020, 08:16:40 am
content: I did a quick inspection of the board. But will have a closer look again.TiN ar you saying that i could still get a -66503 verision refurbished/tested from keysight?Where ? At what price?I did let the unit run for about 10 days and if i remember it right the situation got worse.I want to do a longer run with logging. But before i do that i want to be sure that power supply incl. all relevant components are in good health. Dont want that ugly smoke coming out when i am not around...I think that my board is the oldest version. Pictures attached.RegardsJoerg

author: MiDi
author_rank: Frequent Contributor
timestamp: February 17, 2020, 10:00:35 am
content: Not long time ago the refurbished A3 were orderable from service Homepage at keysight.I do not have the link on hand, but I think it was posted in the 3458 black thread.

author: Dr. Frank
author_rank: Super Contributor
timestamp: February 17, 2020, 11:22:54 am
content: The refurbished A3 boards probably were also not offered any more, as far as we have found out.The new designed RoHS compliant A3 board is in series production already since Spring last year, and therefore this is the only version left for spare parts.And yes, all new boards are fully backward compatible.Frank

author: TheSteve
author_rank: Unknown
timestamp: February 18, 2020, 10:50:53 pm
content: Keysight stopped selling the refurb A3 boards a while back. They then sold them again after a few phone calls but it seems that it was short lived and there is no longer anyway to buy a bare A3 board. They offer only a service option.

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: February 22, 2020, 08:44:14 am
content: Hello - I have been following the price evolution of the A3 board over last couple of years:03458-69503 755€ (One board – through hole components)03458-66513 1258€ (multiple stacked boards)03458-66523 2046€ (SMD version - WEKOMM")03458-66533 1004€ ... 1068€ (SMD version - KS as used in black edition)Yes - the public sale of these A3 boards is set on hold for an undisclosed reason.Also the 03458-66529 VREF board with 2ppm HFL spec was withdrawn despite market demand.Also new A9 DC Reference boards are listed:03458-66539 PC Assembly-DC Ref Tested 8ppm 469€ (orderable)03458-66549 PC Assembly-DC Ref Tested 4ppm 469€ (orderable)We spotted same price info for both 4ppm and 8ppm board on KS site.These superseed the 03458-66509 and 03458-66519 DC Ref boardsHerzliche Grüße/Meilleures salutations/Best regardsScoobyDoo

author: notfaded1
author_rank: Frequent Contributor
timestamp: February 24, 2020, 04:48:37 am
content: I just looked it up on USA Keysight found same basically. Not in stock and the price is the same?which would you choose lol

author: rastro
author_rank: Frequent Contributor
timestamp: February 24, 2020, 02:48:24 pm
content: Sounds like KS is may be using the supply of new boards for their 3458A Black rollout and keeping the stock of older boards/refurbish to support units that are sent back for repair.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 24, 2020, 05:26:23 pm
content: Quote from: notfaded1 on February 24, 2020, 04:48:37 amThere may be a small down side to the 4 ppm reference. I have not checked the specs, but chances are the high stability reference runs at a slightly (e.g. some 10-20 K) lower temperature and this would also mean that the maximum environmental temperature is lower. Not a problem for use in an air conditioned lab, but it could be in a hot environment in a populated rack with additional heat sources. So chances are the 4 ppm/a version would be better for most, but not for all.If the main difference is a slightly different resistor value, there is no need for a different price.I can somewhat understand they don't want to sell the new A3 board. As a service only option they can do a few more checks to make sure the new board really works OK in older units. Even if designed as a 100% replacement a few more checks may be needed until they have enough experience. Even with ACAL one may still want a new calibration after such a repair - so the meter would have to be send out anyway. For large customers who can do the calibration in house Keysight may make an exception, though they may still out a meter for repair.

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 24, 2020, 08:07:53 pm
content: I have a 4ppm reference in my 3458A and it has the same 15k resistor.

author: TiN
author_rank: Super Contributor
timestamp: February 25, 2020, 01:53:53 am
content: All A9 variants use same 1k/15k oven setpoint resistors, there is no BOM difference, only selection process.

author: notfaded1
author_rank: Frequent Contributor
timestamp: February 25, 2020, 03:35:52 am
content: I would for sure order the 4 ppm model if the prices are correct. My lab is almost constant 74°F in the winter and 76°F in summer. I live in desert of the southwest USA in Arizona with always low humidity. On another note to partner with my 3458 I bought this today. I'm still building some my own references because it fun to build things and a hobby for me. I found out the seller ran a lab and was selling all his gear because of a death in the family. I asked the seller to include any history he has on the 732A as well and he's shipping it in a foam blown thick walled box. Unfortunately it hasn't been powered the whole time... I couldn't get that lucky... not for what I paid.BTW... you forsaw this TiN. I've got some nice resistance decades but... how can I not want a certain certain 10K.Bill

author: voltampere
author_rank: Regular Contributor
timestamp: April 05, 2020, 01:24:53 pm
content: I owe you some graphs.First one is from my healthy 3458A.Second is the "sick" one.I did one measurement every 20 minutes. Temparature ( command "TEMP?" ) is the orange line. You can see the daily temp rise in the afternoon when the sun is warming the room that has a window to the southwest. The big temp excursion happened when i got bored and started the Datron 4700 which immediately heated the area around the Equipment by another 2 degrees. That is followed by a sharp drop wheni opened the window to let some fresh air in.The cal constant ( command "CAL? 72") for DCV 10 gain is the blue line.The good meter has a bit of drift but that should be in spec. Less than 0.5 ppm in 4 days. It has a negative temp coefficient.The sick meter has a positive temp coefficient and a strong drift. 2.5 ppm in 4 days. That is around double what is acceptable according to keysight Appnote.I bought a fresh spare board from KS germany and have the sick board on the table now.That brings me back to the questions of my starting post.Does it make any sence at all to try and fix/cure the sick board?I am thinking about to give it some temp treatment. One hour in the oven at 60 deg celsius.Any strong advice against this experiment?Somebody mentioned a possible bad/cracked solder joint.Should i try to reflow the U180 pins?Any better ideas?Best regardsJoerg

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 05, 2020, 05:59:52 pm
content: The sick board seems to stabilize somewhere, after some days, but anyhow, that's what TiN also encountered on one of his bad A3 boards, years ago already.That U180 really seems to be defect.TiN also tried everything to treat it somehow, long stabilizing on-time, temperature shock, he even opened the chip and tried to replace some of the resistors inside.. no chance (in German: vergebliche Liebesmüh).Maybe you search on his site for his experiments, or somewhere here, in the accompanying blog.Sorry. Frank

author: voltampere
author_rank: Regular Contributor
timestamp: April 05, 2020, 06:18:44 pm
content: Right, from the plot one could imagine that it would settle. Maybe...But then you still have this terrible tempco.I think i read every info on TIN's site regarding 3458A in general and also the A3 board and U180 problem.Did not really expect someone to come up with a successful recipe for healing this board.But i am not ready to throw it in the bin yetregardsJoerg

author: branadic
author_rank: Super Contributor
timestamp: April 05, 2020, 06:31:27 pm
content: What I was told at wekomm is, that there is no magic treatment to heal U180, but they are replaced and boards are then tested, until the board achieves the specs.-branadic-

author: martinr33
author_rank: Frequent Contributor
timestamp: April 05, 2020, 09:26:13 pm
content: You might try logging both meters against a known voltage, see what that gives you. A good ADC board doesn't drift at all in the medium term, and running autocal can shift the voltage by some random (small) amount.So:- hook both meters to a known stable voltage- Log the voltage on both metersIf your voltage is really stable, you will be able to see the drift on both units and also derive your thermal characteristics. If nothing else, the delta between the systems will give you an idea as to how bad your drifty board is.The reason is, autocal injects some noise by shifting reading a little.Then finally - repeat with new board.The reason for the Agilent method is you might not have a stable reference.

author: MiDi
author_rank: Frequent Contributor
timestamp: April 05, 2020, 09:49:16 pm
content: My unit showed initial drift of ~0.6ppm/day for CAL 72, it tookseveral monthsto settle to a reasonable drift rate - now after more than a year it has < 0.04ppm/day.CAL 72 shows a TC of -0.33ppm/K, which is in compliance with some others units I had ability to compare - up to 0.5ppm/K is acceptable for ADC according to HP Journal.

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 06, 2020, 04:30:25 am
content: @MiDi what tools did you use to create that CAL 72 graph?Bill

author: voltampere
author_rank: Regular Contributor
timestamp: April 06, 2020, 06:09:58 am
content: Quote from: martinr33 on April 05, 2020, 09:26:13 pmThat is what i did. It was running away a couple of ppms per week. That is why i go suspicious and started the CAL 72 log.A drift on a log of a stable voltage source should also show up in the change of CAL 72 in my understanding of the ACAL function.MIDI:My eyes ar not good enough to read the horizontal scale of your graph. Is it one week per division?Your meter was on 24/7?RegardsJoerg

author: TiN
author_rank: Super Contributor
timestamp: April 06, 2020, 06:10:49 am
content: voltampereI don't see much drift in your hp3458z plot. Just normal settling for warm-up time.So don't understand where you get conclusion that your A3 is bad.

author: MiDi
author_rank: Frequent Contributor
timestamp: April 06, 2020, 06:55:34 am
content: Quote from: notfaded1 on April 06, 2020, 04:30:25 amThe chart is made with Excel and updated automatically from csv with the captured data.The extra lines and text are inserted manually, the TC compensated dppm are calculated with determined TC of CAL 72.For logging I use RasPi with Linux Gpib and Python program that logs the CAL values every hour into csv.Quote from: voltampere on April 06, 2020, 06:09:58 amMain horizontal scale is one week, starting at 2018-11-26.You can click onto it to get the full resolution and zoom in to read it better, but I have to admit that the horizontal scale labels are getting a bit to small for presentation.Unit is on 24/7 with some exceptions.

author: maat
author_rank: Regular Contributor
timestamp: April 06, 2020, 07:13:05 am
content: I did have a sick A3 board as well, which gave itself away by its awful 0.85ppm/K tempco. At first I assumed, that it was just luck and the board simply had a slightly higher tempco. To get an idea about the tempco I started logging the internal temperature. Since the the TEMP? Command has a crappy resolution I opted to use the higher resolution ACAL DCV + CAL? 175 command, but the resolution is still no god. Ifinally placed a temperature sensor inside the case, that gave similar results and response time. Anyway, since I had the CAL? 72 values now, I plotted them and realised they drifted.The attached plots are post processed. I did a fit with two parameters (time and temperature). The drift plot has the temperature component removed and the tempco plot has the drift component removed.I can also provide the python scripts to record and plot/fit the data, All I need to do is brush them up a little.End of the story: 3 Months later the DMM died with a114,"SYSTEM ERROR -- balanced rundown convergence" during further testing and202,"HARDWARE FAILURE -- "SLAVE TEST: CONVERGENCE" after self test.Lucky me, I had opted for a warranty extension, which KS offered during the last calibration

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 06, 2020, 07:32:17 am
content: Quote from: maat on April 06, 2020, 07:13:05 amHello,have you placed the temperature sensor directly on A3, or on U180?Frank

author: maat
author_rank: Regular Contributor
timestamp: April 06, 2020, 08:08:28 am
content: Quote from: Dr. Frank on April 06, 2020, 07:32:17 amUnfortunately no, because I was trying to mimic behaviour of the "TEMP?" command. I did that, because I assumed, since the tempco was still in spec, that I had to live with it and that I could correct for it using the TEMP? command, once I had a good understanding of how bad it was. Also due to the warranty extension, I did not want to remove the stickers at that point.The sensor (Fluke 5611T, PTFE coated 10k thermistor) was placed on the the inguard metal shield (side) and fastened using Kapton tape. This was as close as I could get with a pair of tweezers and gave near identical results to the TEMP? command, albeit better resolution.

author: voltampere
author_rank: Regular Contributor
timestamp: April 06, 2020, 09:32:38 am
content: Quote from: TiN on April 06, 2020, 06:10:49 amTIN, the meter was running already for at least two weeks or so, if i remember correctly.Still warmup drift???Of course i can not be 100 % sure that the board is out of spec.Maybe i was too impatient. Maybe i have to let it run for half a year and see where it ends.Or try to accelerate the drift process with some baking in the oven?RegardsJoerg

author: Kleinstein
author_rank: Super Contributor
timestamp: April 06, 2020, 09:52:27 am
content: No need to stress the board, as we do not know where the acceptable limit is for the higher temperature. It would be more like watch the ADC for a few weeks. The 2.5 ppm in 4 days is still boarder-line, just a little over the limit. The typical bad ADCs seem to be way higher drift.I think the 0.43 ppm/day limit is more like a value that all good ADCs still meet this limit. There can be temperature and maybe humidity effects so that it may just need more time to get a reliably value for the drift. So maybe better read it as 6 ppm in less than 2 weeks.The ADC gain drift is only one symptom of a drifty U180. The actual real problem is more with other resistor ratios. The CAL72 is just the one that is easiest to measure. So a drifty A3 board can also show higher DNL errors, more TC or similar effects.

author: maat
author_rank: Regular Contributor
timestamp: April 06, 2020, 12:13:35 pm
content: In my opinion, the 0.43 ppm/day drift rate is a rather weak criterion, because a good ADC definitely drifts less 0.1 ppm/day. The SN-18 unfortunately is a bit superficial on this issue. As was KS, when I nagged them about the issue.The problem is, that in order to properly determine a drift you needa failry stable lab, so you don't see any 5 or 10 K excursions, have humidity going on a rampage when the weather turns and so onto to have to instrument turned on 24/7 for at least a month or twoto continuously monitor both temperature and the calibration constantsapply a 2d fit to determine both tempco and driftUsing the method suggested by HP/Agilent to determine the drift reduces the problem to taking two samples 7 days apart, without proper temperature monitoring, therefore the error margins are fairly high. A 1 K drift is typicall deemed acceptable, and T_cal ± 5K is the normal working range. On the other hand continuously logging will take the instrument out of service, which might not be acceptable. From the style of writing I would also assume, that HP did not anticipate, that all users are capable or willing to properly extract the drift of their instrument. So my guess would be, that 0.43 ppm/d drift is a dying DMM slapping in your face and not a marginal situation, but it can be easily measured, hence not many false positives.

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 06, 2020, 01:03:44 pm
content: Quote from: maat on April 06, 2020, 12:13:35 pmThis 0.43ppm/d criterion is just the interpolation of the timely drift specification of about 8ppm/year, down to 24h.If you apply a square root function for the ageing of the LTZ1000A reference: dU/Uref~ 8.2ppm * SQRT(t / 8760 hr), then for 24h you get 0.43ppm drift, 90days would be 4.1ppm, and 2 years 11.6ppm, about the values given in the specification.There's no official specification for the short term stability of this instrument, neither for the T.C. of the A/D converter w/o ACAL.Therefore no wonder that KS is close-lipped about these (internal quality) criterion.'Normal' or 'healthy' values are a vanishing timely drift for CAL?72, practically meaning you can't barely distinguish it from fluctuations, or T.C. effects.And a T.C. of about +/- 0.35 ppm/K for U180, and +/- 0.5ppm/K in total, i.e. ~ +/- 0.15ppm/K for the LTZ1000A, regarding these T.C.s, see specification.My 3458A behaves exactly like that, therefore an absolutely stable room temperature dT << 1K is required.Frank

author: maat
author_rank: Regular Contributor
timestamp: April 06, 2020, 03:32:19 pm
content: Quote from: Dr. Frank on April 06, 2020, 01:03:44 pmAbsolutely true, which is, why I called it "weak", because from the two datapoints, that one is supposed to take, a correct interpretation is difficult.Regarding my old A3 board, I monitored it over the course of a month or so and the drift was linear with few wiggles due to the temperature compensation not being 100% accurate. All I wanted to say is, that one should monitor the drift over some time. Typically after about two days the statistics were good enough and they fit converged nicely.The new (I don't know if it is one of the all new, or just refurbished. I haven't had a look at it yet) A3 board hardly drifts and the tempco is excellent. I had a chance to measure it while I was measuring a Vishay 300144ZT divider in ratio mode and the air con went offline and the the emergency mode kicked in pulling the temperature down. The absolute ratio was 10 V * 17/(20+17) = 4.59 V and the divider is not responsible for the drop, because it was in the isothermal chamber during that time.

author: TiN
author_rank: Super Contributor
timestamp: April 06, 2020, 11:51:45 pm
content: QuoteI would consider 3458A coming from cold essentially in infancy first 3 month. Somewhat useful data can be gathered after monitoring these 3 month in 24/7 operation. When you trying to split sub-ppm deviations on voltage, look in wrong direction may upset the poor instrument.QuoteJust continue monitoring in stable temperature conditions and see where you end up after 4 weeks.QuoteAbsolutely not. Why ruin possibly good just unwarmed board with overstress? Baking anything in oven is great way to certainly kill what is not dead yet.Don't take example from my experiments with freezing and heating, because I was 100% sure that unit is very dead, as it would not even sample anything due to integration errors. So unlike you, I had nothing to loose.

author: voltampere
author_rank: Regular Contributor
timestamp: April 07, 2020, 10:13:42 am
content: Well, if i speak of "baking" it would mean that i put in in the oven at 60-70 degrees celsius!Not like 100 deg or above. Just to help it with accelerated drying.But you guys convinced me!Before i start playing desperate experiments i will give it another shot in a marathon warmup watch.Though i really doubt the success. I bought this meter about a year ago.And i am pretty sure that i had it on for extended periods a couple of times already.Anyway, it sure does not hurt, and costs only electricity ( maybe 15-20 € ).So i should be back here in a bit more than a month and tell about the outcome.Thank you all so far..RegardsJoerg

author: niner_007
author_rank: Frequent Contributor
timestamp: May 18, 2020, 07:11:31 am
content: I don’t know how it’s in Europe, but in US, absolutely smooth, I had the part number, they explained all other part numbers, and options, and they could even order from stock outside US, I had ordered 4 IIRC. It costed $1700 - $2000 brand new, and $700 for the refurbished one.

author: ap
author_rank: Frequent Contributor
timestamp: May 18, 2020, 10:31:47 am
content: Was that recently? I bet not. It has changed a few months ago (at least here), they stopped selling these outside of service orders. Would be interesting if thats not the case in the US at this time.

author: CalMachine
author_rank: Frequent Contributor
timestamp: May 18, 2020, 07:26:16 pm
content: Quote from: niner_007 on May 18, 2020, 07:11:31 amI just tried to order the 3 ADC boards and they told me none of them are available. This was, literally, 10 minutes ago

author: niner_007
author_rank: Frequent Contributor
timestamp: May 19, 2020, 01:35:42 am
content: oh wow, good that I have my stash then

author: niner_007
author_rank: Frequent Contributor
timestamp: May 28, 2020, 08:53:46 pm
content: I can confirm this as wellI have a 3458A that reports ADC connection errors, I'm not going to use an ADC from my stash for this, I started a contract with Keysight. I guess overall, it does not seem that expensive and it's reasonable. I can only guess what this would be with Fluke

author: e61_phil
author_rank: Frequent Contributor
timestamp: May 28, 2020, 09:01:36 pm
content: Quote from: niner_007 on May 28, 2020, 08:53:46 pmHard to judge. Maybe we will know that better sometime. As soon as Fluke also build ADCs in their instruments which dies like flies.

author: niner_007
author_rank: Frequent Contributor
timestamp: May 29, 2020, 05:46:50 am
content: Quote from: e61_phil on May 28, 2020, 09:01:36 pmMine is not drifting, it is dead

author: Kleinstein
author_rank: Super Contributor
timestamp: May 29, 2020, 08:27:51 am
content: If the meter report a connection error, this may be a different failure. Best case just a loose fiber optic connector. There were also reports about those fiber optic parts to fail. So this could be a repairable failure that does not involve the custom U180 chip.AFAIK the failing U180 first causes drift (and possibly some INL errors - so compensation with more frequent ACAL is not a real option) and later the convergence error, when the error gets too large.Having a new ADC board installed at Keysight and not done by the user is not so bad, if the extra costs are not outrageous. After such a repair one would need a new calibration anyway, so in most cases the meter would have to be send out anyway.

author: IanJ
author_rank: Unknown
timestamp: May 30, 2020, 12:15:46 pm
content: Quote from: Dr. Frank on April 06, 2020, 01:03:44 pmI have been logging CAL? 72 to a spreadsheet on mine since Oct. 2018 and which outputs Drift PPM (referenced to Day 1). I have 30 samples across 562 days. The conclusion was that........there was no conclusion!With my workshop temp varying and the resultant Temp? ranging from 32.6 to 38.3 DegC it's really hard to make anything of the results. The only thing I have been able to read from the results is pairing up similar/identical Temp? readings from different days and comparing the Drift PPM figures, and if they are pretty close then I assume my board is ok.I often wondered if there was a way to make a big enclosure/box for the 3458A to sit in that is perfectly temperature controlled.........but probably too much trouble.Ian.

author: MiDi
author_rank: Frequent Contributor
timestamp: May 30, 2020, 02:18:25 pm
content: If the drift is low and nearly constant you should be able to calculate and compensate for TC.I did that in my ACAL measurements since Dec 2018 and included CAL 175 (high-res Cal-Temperature).Now I know my unit has ~ -0.33ppm/°C TC and settled to drift rate ~ -0.03ppm/day for ADC (CAL 72) - if the filter is cleaned regularly- see attached chart.Edit: This is a follow up tomy post 2 months earlier- probably I do not bore you with it for longer period anymore

author: niner_007
author_rank: Frequent Contributor
timestamp: July 19, 2020, 11:46:00 am
content: My repaired/calibrated 3458A is coming back from Keysight on Monday, exciting!

author: dietert1
author_rank: Super Contributor
timestamp: July 20, 2020, 08:46:00 am
content: @ Midi: Since i am not familiar with 3458A, could you write a sentence what the measurement is? As far as i understand this is not a comparison between two references, but a cross check where the ADC measures its own reference. Is that correct? The second curve with larger fluctuations, is that the temperature sensor?Regards, Dieter

author: MiDi
author_rank: Frequent Contributor
timestamp: July 20, 2020, 09:43:48 am
content: The diagramm shows the cal values stored from instruments calram for last (A)CAL, here it is executed every hour.Cal 72 is gain correction, which afaik is calculated from measurement of the internal voltage reference - light grey line in diagramm as deviation in ppm.Cal 175 gives internal temperature - blue line.The black line is temperature corrected Cal 72.Would be interesting to have a comparison of ADC TC for couple of older and newer A3 boards - have the newer lower TC?

author: Kleinstein
author_rank: Super Contributor
timestamp: July 20, 2020, 03:05:33 pm
content: The average TC should be close to zero, just the scattering may be slightly different. Besides temperature there can also be an effect of humidity / board stress so it is not just temperature. However it takes lots of samples (meters) to judge on scattering. The special chip is still the same - so likely not much change - maybe with batches.

author: dietert1
author_rank: Super Contributor
timestamp: July 20, 2020, 05:01:41 pm
content: What i see there are surprisingly large total shifts of several ppm and an exponential decay of drift with a time constant of 2 years or more. I have seen both with thin film resistors, so i would guess that ADC is a hybrid and the resistor arrays in it cause those shifts. How old is that ADC assembly?I can also see that by cleaning the fan/filter and applying simple numerical TC and drift compensation, the ADC performs to a standard deviation of less than 0.05 ppm (residual in straight parts of the black line). Do you have similar numbers for the behavior of the reference in that instrument?Regards, Dieter

author: MiDi
author_rank: Frequent Contributor
timestamp: July 20, 2020, 06:45:52 pm
content: My unit has datecodes from end '89, everything is original, only a couple of replacements were made -details in 3458A worklog thread.The U180 is a hybrid consisting of a resistor array and switches, adie shot of U180 is somewhere in one article of 3458A on xdevs- Edit: added link to die shot fromxdevs article.It is not so easy and costly to determine drift of reference with low uncertainty, but soon I want to post some data of the unit.

author: dietert1
author_rank: Super Contributor
timestamp: July 21, 2020, 05:07:13 am
content: For an old instrument even slow aging should have come to an end, except if it depends on operating temperature and the instrument was essentially off all those years. Did you think about trying a TEC pile on that ADC hybrid U180? I mean if the firmware of the 3458A does not support temperature and drift corrections, maybe you can do it by chip temperature control. If aging depends on chip temperature, one could try running that chip a little cooler.Before trying mods on an expensive instrument i would decide upon a certain goal in terms of ppm/year or so.Regards, Dieter

author: MiDi
author_rank: Frequent Contributor
timestamp: July 21, 2020, 11:35:44 am
content: Not shure what you mean by "aging should have come to an end", even best secondary standards are drifting after aging for dozens of years (e.g. SR104, 732x)If the drift rate is known, quite stable and somehow predictable you are able to include that into the calculation of measurement result and uncertainty - same applies for TC.I doubt it is worth the effort in trying to compensate for drift and/or TC for U180 - imo ACAL already does this (and much more) satisfactorily.Keep in mind, 3458A is not a secondary standard - the internal references are not designed for best TC nor drift, but it is one of the best ratio measurement instrument.

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 21, 2020, 08:09:37 pm
content: Quote from: dietert1 on July 21, 2020, 05:07:13 amHello Dieter,Midi already wrote it as it is: No DMM is intended and accepted as (secondary) standard.The 3458A is used in metrology mainly as a ratio machine for transfers, due to its ultra linear A/D.Its voltage reference is neither optimized for timely, nor for temperature drifts.As it's got 90°C oven temperature, drift would be usually about -30ppm/yr, but the complete modules are monitored and selected for annual drift of 8ppm, 4ppm or until recently 2ppm/yr.The standard reference will usually drift less, like 2ppm/yr., after one or two years, it's rumored.But it will not approach zero.All drift specifications are valid for continuous operation, so it's probable, that the drift is very low when not in use, and if no hysteresis effects occur.But even real voltage references, like the 732A/B/C, or the M7000, running only at 45..55°C, mostly show a constant drift, after years of operation. The LTZ1000 drifts typically -0.8ppm/yr., and might settle down to - 0.5 ..-0.2 ppm/yr.hp did not even trim the module for zero T.C., so the, I think, 0.3ppm/K are quite mediocre.With a little bit of effort, it could have easily be tuned to 1/10 of that value.The U180 has additionally about 0.5ppm/K, which can easily be compensated by the ACAL procedure.hp did not intend to design a real metrology instrument, that's obvious.So a bit of tuning can be done, like decreasing the oven temperature, maybe compensating the T.C. of the LTZ circuit. But then the story ends, and you better get a real 10V standard, which you might use for comparison, or for frequent calibration of the DCV mode.Frank

author: dietert1
author_rank: Super Contributor
timestamp: July 21, 2020, 09:40:14 pm
content: Yes, i understood that the 3458A has a firmware procedure "ACAL" that takes care of ADC temperature and time drift. Anyway, this thread is about the risk of loosing the ADC and apparently an observed drift of 0,03 ppm/day (about 10 ppm/year) of the ADC alone makes people nervous. That's why i am asking: At which temperature is that ADC hybrid running? Is the temperature sensor of the instrument inside that hybrid?Side remark: Tektronix 2465 scopes have a notorious hybrid U800 failure. It also happened in our lab and after fixing the instrument and solving the underlying heat/mount problem i thought: What a stupid mistake in an otherwise wonderful design.Regards, Dieter

author: Kleinstein
author_rank: Super Contributor
timestamp: July 22, 2020, 08:46:45 am
content: The U180 hybrid should have low power loss and should thus not run much hotter than the general board. The problem is not so much the normal drift rate (e.g. < 0.1 ppm/day). This is easy compensated by ACAL every day or so. If the instrument was not in use for some time there may be additional drift for some time, but this would settle after a few days / weeks.The problem is a possible and not so rare defect in U180 that is first visible as a much higher drift (often > 1 ppm/day). Chances are after some time the ADC would not work at all. So compensating this higher drift rate is not helping. The drift is only the symptom of a slowly failing ADC that is easiest and early to detect. So one can get an early warning, before the ADC will finally fully fail. With the high drift rate I would not fully trust the ADC anymore, as there can be other problems like higher DNL.

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 22, 2020, 02:19:22 pm
content: Quote from: dietert1 on July 21, 2020, 09:40:14 pmPlease first have a look into the Service Note 18, the criterion by hp was 0.43ppm/day (not 0.03ppm/day).There are two flaws in this,1) This 0.43ppm/day criterion is too big, only safeguarding the daily specified timely drift of the LTZ1000.2) this CAL? 72 parameter is also temperature dependent, that is not mentioned. As the usual T.C.s of the LTZ and of the U180 itself are in the same ballpark or even exceed this drift rate at reasonable lab temperature stabilities, its hard to separate this timely drift effect of U180 from these temperature drift effects.It can be done with a lot of statistics, including the interior temperature, TEMP?.Unfortunately, this T-sensor sits on the analog board on top, whereas U180 is located upside down on the bottom part of the instrument.I think this issue is:Frank

author: e61_phil
author_rank: Frequent Contributor
timestamp: July 22, 2020, 02:30:47 pm
content: I don't understand why they consider the LTZ1000 drift. A drift of the LTZ1000 shouldn't influence CAL72.

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 22, 2020, 03:46:03 pm
content: Quote from: e61_phil on July 22, 2020, 02:30:47 pmThat's right.hp at that time simply used the drift specification: 24h / 90d / 1yr. (caused by the LTZ1000A drift) as a criterion for the allowable drift of U180, as latter daily drift should not exceed that specification either.0.43ppm/day is the exact drift rate of the LTZ, interpolated to 1 day, if an annual drift of about 8ppm/yr. is assumed, and a square root drift dependency is used.Frank

author: dietert1
author_rank: Super Contributor
timestamp: July 22, 2020, 05:39:29 pm
content: Whatever Agilent/Keysight write, Midi's records demonstrate the ADC aging isn't a random process but something else and very regular. And it does reach 10 ppm/year at a daily drift rate of 0.03 ppm in his case. Hard to believe nobody tried to find out what that process is (and how to stop it).Regards, Dieter

author: Villain
author_rank: Regular Contributor
timestamp: July 22, 2020, 06:21:29 pm
content: Quote from: dietert1 on July 22, 2020, 05:39:29 pmWhy would anyone make the effort when the 3458A is not a primary standard anyway (and not intended to be).If i want more accuracy for DC i hook up a Fluke 732 and do a differential measurement using the transfer accuracy of the 3458A. Thats a sub-ppm measurement right there, no need to go through the trouble trying to get the 3458A in that region by itself.edit: Or don't use a 3458A at all, only 732, dividers and null detector.

author: niner_007
author_rank: Frequent Contributor
timestamp: July 23, 2020, 02:05:24 am
content: My 3458A came back from Keysight. They replaced A1 DC board, A3 ADC board, and A7 display board, the EMI filter, fan, and mechanical switches. This is very thoughtful actually, so I have a new display tooThis was all included in the initial repair service contract, amazing experience. I've sent it in a pretty shitty box, and it came back in this amazing boxThey tested and calibrated, and declared it "like new" factory state. This is greatThe cal data looks amazing. Now we'll see how it drifts. I'll take it apart at some point to see the replacement boards, but hesitant given the very nice cal sticker on the screws.

author: Villain
author_rank: Regular Contributor
timestamp: July 23, 2020, 02:42:38 am
content: Quote from: niner_007 on July 23, 2020, 02:05:24 amWhich Keysight Lab did you send your 3458A to?

author: dietert1
author_rank: Super Contributor
timestamp: July 23, 2020, 05:18:18 am
content: Quote from: Villain on July 22, 2020, 06:21:29 pmTo protect his investment. If that non-stochastic drift process is the one that finally destroys the ADC, as was argued before. It's nice that you can get a repair, but it's bad if the instrument has a built-in failure mechanism like those Tektronix 2465 scopes i mentioned before.Regards, DieterPS: For example before i buy a 3458A i would ask: Is there a numerical limit in the ACAL procedure? Maybe ADC failure just means that ACAL arrived at a 100 ppm limit or so. Then you can predict how long it will take.

author: niner_007
author_rank: Frequent Contributor
timestamp: July 23, 2020, 05:21:35 am
content: Quote from: Villain on July 23, 2020, 02:42:38 amit was Loveland, CO

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 23, 2020, 11:36:22 am
content: Quote from: dietert1 on July 23, 2020, 05:18:18 amDieter,your arguments are very weird.That small drift does not 'destroy' the U180, or the A/D at all.You would probably also not argue, that the drift of gain resistors in other DMMs like in the FLUKE 8508A, 8588A, etc. would finally destroy these instruments.If you find an excessive drift which would approach or exceed the 24h stability limit, then KS will replace the board, maybe on guarantee under given circumstances, but that's the normal process with failures on any instrument, I thinkAlso this theoretical drift of 0.03ppm/day will never sum up to 10ppm/year.Please first read carefully the specification and manual of the 3458A: All specified drift parameters require, that ACAL is used every 24h, or whenever the temperature changes by more than 1°C.You might need to understand that the 3458A uses cheaper components, therefore requires frequent ACAL, whereas the DVMs from FLUKE make heavy use of expensive and very stable MBF or hermetic NiCr resistors, to give similar stability figures, but w/o an ACAL process.The FLUKE 8508A, like the Datron 1281 were much more expensive than the 3458A, and could therefore not compete as industrial use DMMs.I don't think that these companies buying the 3458A ever feared that their investment was in danger, as a 3458A with a properly working U180 simply fulfills its specification.If you were still afraid about any small drifts, which are quite natural, then I give you the advise to never buy a 3458A, but also not any other long scale DMM.Frank

author: dietert1
author_rank: Super Contributor
timestamp: July 23, 2020, 01:14:34 pm
content: @ Frank: 0.03 ppm/day times 365 days/year gives 11 ppm/year. That is anobservationof Midi, please look at the diagram posted above. Let's stick to facts.Regards, DieterPS: I guess Midi posted his findings in this thread because he was afraid of loosing his ADC. It's not about me.

author: MiDi
author_rank: Frequent Contributor
timestamp: July 23, 2020, 03:01:19 pm
content: Quote from: dietert1 on July 23, 2020, 01:14:34 pmEssentially no, but I would not consider 0.03ppm/day drift for ADC fully healthy.Not shure why you got that impression from my postsInitially when I got my unit, there was indication of faulty ADC, but after some month of logging this vanished.

author: dietert1
author_rank: Super Contributor
timestamp: July 23, 2020, 03:24:09 pm
content: A tracking drift of 11 ppm/year for a 30 year old thin film array appears strange, should be less than 1 ppm. Good ones (still "cheap") are less than 1 ppm when new.So there could be a deterioration of the ADC silicon and if that is true, it may worry any potential buyer of a 3458A, considering the cost of such repairs. If the deterioration is slow, it will normally be hidden under the ACAL procedure for a very long time, so the problem will only be visible after warranty expired. How much was that "refresh" mentioned above?Regards, Dieter

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 23, 2020, 06:59:28 pm
content: Quote from: dietert1 on July 23, 2020, 01:14:34 pmSorry Dieter,your arguments are getting more and more weird.Obviously you really do not understand the specification of, and the technology used inside the 3458A.The 3458A has a specified drift of 8ppm/year or 4ppm/year for the hi stability reference. This is usually met, because the ACAL procedure every 24h is ultimately required.The timely drift of the internal A/D resistor network plays absolutely no role. It's also not specified anywhere, as far it's not exceeding the 24h drift specification (defined by hp).Therefore the ordinaryl U180, indicated by parameter CAL? 72, might drift 10ppm/year, or much more, but that is absolutely irrelevant, for the 'sanity' of the instrument, for the short to midterm drift, and most important, for the given specification of the instrument.Latterwill stay always below these 10ppm/year, because ACALmustbe used. That's what I wanted to point out initially.If you would simply judge the state of this instrument from its specification limit, only that would be really 'sticking to the facts'.Sorry again, but you are arguing about a non specified parameter, which also has absolutely nothing to do with the real, practical use of this instrument.Additionally, a theoretical 0.03ppm/24h drift is not relevant at all on a daily or even weekly time scale.. please take into account realistically, how stable analogue DCV standards (eg 732B) are in reality... such a small drift will completely vanish in the noise floor.Therefore, I would call 0.03ppm/24h for the U180 a really stable and healthy instrument.Frank

author: MiDi
author_rank: Frequent Contributor
timestamp: July 23, 2020, 08:31:24 pm
content: Quote from: dietert1 on July 23, 2020, 03:24:09 pmDetails please, sounds to good to be true

author: dietert1
author_rank: Super Contributor
timestamp: July 23, 2020, 08:49:23 pm
content: No, of course it matters for a buying decision if there are reports about drifting or failing ADCs in 3458A voltmeters, especially since the ADC seems to be the better part of that instrument. You don't have to repeat Agilent/Keysight advertising.The question for the limits of the ACAL procedure is completely valid and i haven't seen a useful answer. As the existence of this thread shows, there may to be a gray zone, where the ACAL procedure is hiding real problems until it is to late.As far as i remember 1 ppm is the tracking limit of LT5400 resistor arrays, which have been used by others to make high resolution ADCs. Those are specified with tracking of 0.2 ppm typical. My own experiments with Nomca resistor arrays gave an upper limit on tracking stability of about 0.03 ppm over twelve weeks. That would be 0.12 ppm after a year, if it were a continuous linear drift like your 3458A ADC.Regards, Dieter

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 23, 2020, 09:42:40 pm
content: Quote from: dietert1 on July 23, 2020, 08:49:23 pmDieter,Please do not accuse anyone, and especially not me, to repeat advertisement of the companies in discussion.That's at first not correct, as I simply cited the specifications, and 2nd it's a sign that you've run out of reasonable arguments.You're arguing about an assumed failure of the 3458A, which in reality has no real practical relevance.I'm missing your practical use case, for which this might be relevant, i.e. beyond the specification.Please explain your use case, otherwise I'd recommend to stop this useless discussion.Frank

author: Kleinstein
author_rank: Super Contributor
timestamp: July 24, 2020, 05:48:48 am
content: A 0.03 ppm/day drift looks relatively high. However this is not just a single resistor ratio, but there are 2 ratios involved (the one from the reference scaling about 70% effective). The observed curve from Midi shows some slow down in the drift. This may not be a typical instrument. The ACAL procedure can compensate for such a drift in the resistors, though there are limits.The feared ADC failure is a different thing, and drift of the gain is only one symptom. With a more frequent ACAL one could probably still use the 3458 with a drift of some 1 ppm/day - however there are other problems waiting to happen, probably trouble with the lesser slopes and thus failure in ADC convergence in the time limits.The failing ADCs are a weak point for the 3458. There are quite a few reports of such failures. The used instruments from auction sites may include quite some meters that are sold because they showed first signs of the failure or other faults. So there failure rate is naturally higher. There are also the comparators that may fail on the ADC board.Because of the ADC failures it is important that replacement parts are still available. The old, multi-board-design at least allows partial replacements. A failing ADC in an 34470 or DMM7510 would be hardly repairable, except for the very skilled volt-nuts. Modern electronics also tends to be more reliable. Maybe we can hope that the black edition also got better in this respect.

author: dietert1
author_rank: Super Contributor
timestamp: July 24, 2020, 06:06:07 am
content: No, i have not run out of arguments. Just wrote down some information to show that there is no good reason why a 3458A ADC should drift at 11 ppm/year. Can't others contribute any information to solve this riddle?Regards, Dieter

author: niner_007
author_rank: Frequent Contributor
timestamp: July 24, 2020, 11:27:02 pm
content: Quote from: dietert1 on July 24, 2020, 06:06:07 amGet it fixed, get a service repair agreement, what's the problem?

author: dietert1
author_rank: Super Contributor
timestamp: July 25, 2020, 05:24:38 am
content: Apparently nobody understands how to fix it or they keep it secret to charge again and again. They just replace the ADC module but the new one may behave similar.On the xdev.com site there are thermal images of a 2015 ADC board (IR000326 and IR000330) and it has a hot spot: The fast comparator on its patch board, which was measured to run at 75 °C (after opening the cover). With the covers closed it probably runs at 80 or 90°C and one could apply an IC cooler to bring this down and see whether it helps. Older ADC board revisions have a different comparator chip and it sits in the ADC board, but it also has a consumption of about 600 mW (20 mA x 30 V).Regards, Dieter

author: niner_007
author_rank: Frequent Contributor
timestamp: July 25, 2020, 06:14:56 am
content: Do you or we (in the forum) have statistics on the failure rate? If we don't, it could well be anecdotal, sorry, but it's just that simple

author: MiDi
author_rank: Frequent Contributor
timestamp: July 25, 2020, 06:40:47 am
content: Agilent had quality problems with U180, look atSN18A.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 25, 2020, 07:11:46 am
content: The Elantec comparators are a different critical point. They are fast and use quite some power for this, so they run hot. These comparators are also know to fail sometimes, though not sure why. The daughter-board is a fix to replace 2 single comparators (with very poor availability) with a single dual version that for some reason had better availability. The dual version naturally runs even hotter. The 3458 has a fan and thus may not run hotter with a closed lid - it may even run cooler for some parts.Anyway the new SMD version changed the comparators to a different type.

author: martinr33
author_rank: Frequent Contributor
timestamp: July 25, 2020, 05:49:15 pm
content: If you have a 732a or silimar super stable voltage source, a drifty ADC shows up very quickly. A ppm of drift is 10uV.I don't know that sellers really know whether or not the ADC is bad. If you do a regular autocal, and are not monitoring stable sources over several days, you would never see it. Also, if you use the machine only occasionally and keep it turned off, you would not see it.Certainly, when you buy a unit on eBay, you might have been looking at a $1200 ADC repair. Now, you cannot get the ADC. Based on the units from eBay I know about, 25% or so are bad.

author: ap
author_rank: Frequent Contributor
timestamp: July 25, 2020, 05:58:04 pm
content: Unfortunatelly, the ADC drift issue seems not to be anecdotal. My personal experience, this affected more than 50% of the units I had in hands (used, older and newer ones), and it is all over the place, including A3 units bought from KS (which they then replaced). Have not done a formal statistic (should have), my personal summary. So beware of buying used 3458As without having the right to return drifty ones.

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 25, 2020, 06:22:58 pm
content: Quote from: ap on July 25, 2020, 05:58:04 pmHello Adrian,I know and appreciate your experience already, as you also trade these used instruments. So what is your 'hard' criterion (boundary specification) of a 'drifty' U180? How many ppm/timescale is ok for you? What do you base your judgement on?I think, w/o well-founded arguments about what is really relevant for the performance of the 3458A, namely its final specifications, such diffuse statements, also such as from Dieter and Kleinstein, that will only cause confusion and uncertainty on owners and possible buyers of this instrument. Also, please claim your use case, what a more or less stable U180 should be good or bad for.. every other discussion is only of academic nature.In this context, I'd like to suggest to again read the hp journal 4/'89, p. 13 ff, where the design engineers nicely explained the design goals of the A/D circuit, especially the U180 drift and matching requirements. That may help to get some realistic expectations about this circuit.P.S.: Your advice, to imply the right to return 'drifty' 3458As might only be worthwhile, if there would be a reliable, commonly accepted criterion. Maybe you can share your personal experience, in discussions with business partners, or with Keysight.Frank

author: dietert1
author_rank: Super Contributor
timestamp: July 25, 2020, 07:48:30 pm
content: Maybe that criterion can be derived by comparing the 3458A ADC to that of other long range DVMs. For example i can contribute an ACAL check measurement from our 3456A multimeters: Connect input to its own voltage reference. For me that is something easy to do. Make some measurements at different temperatures during the next days and repeat after three months to determine the drift.It will take time to get the result, but in the end i think everybody would agree that a 3458A ADC should not drift a lot more than a 3456A ADC. Anyway there would be some numbers for Midi to compare to. That is the use case. Of course it would be interesting to have results from other 3458A owners, too.Regards, Dieter

author: Kleinstein
author_rank: Super Contributor
timestamp: July 25, 2020, 08:30:47 pm
content: The test HP suggested from the ACAL drift is 0.43 ppm per day, which is 3 ppm for a week. Because of temperature effects is may take more than 1 day to get a reliable drift rate. A week sounds more realistic for the test. Good meters are supposed to be much better, even the 0.03 ppm / day reported by Midi are more on the high side if persisting for a long time.For practical use 0.4 ppm over a day may already be a problem and require quite frequent ACAL.The ADC can tolerate quite some deviations for the slope ratios (e.g. 0.1 % for high speed, 3% for low speed). However the ACAL measurement checks a different resistor ratio. It is only an indirect test in this respect - so the limit for the total drift may have to be tighter (e.g. 100 ppm total drift) to be reasonable sure the other resistors have not changed 1000 ppm.

author: dietert1
author_rank: Super Contributor
timestamp: July 25, 2020, 09:35:28 pm
content: Dr. Frank wrote before that the 0.43 ppm/day number is based on the assumption of random walk (0.43 ppm/day random walk gives about 8 ppm after a year which is the basic instrument accuracy spec). If the drift is continuous and persistent for more than a year as in Midis case, that assumption does not hold. In other words: The observation of a long term continuous ADC drift is far away from what Agilent engineers had seen and means that an ADC board maybe in risk.Regards, Dieter

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 26, 2020, 08:11:22 am
content: Quote from: dietert1 on July 25, 2020, 09:35:28 pmSorry again, Dieter, but this 0.43 ppm/day criterion is not based on 'Random Walk' phenomenom, and I have never said so.Again and again, there was no , and there is no specified criterion for the annual drift of the resistor array inside U180.When this serial batch problem occurred in about 2006, the agilent engineers have used the timely DCV drift specification of the 3458A, which is mostly caused by the LTZ1000A drift, and boiled that down to its theoretical 24h drift. The typical behavior of any thermally induced drift is a square-root one, see article from hp journal 4/89, with an annual drift of 8ppm/yr.So the drift function can be written down as: dU(t)/Uref= 8ppm/yr * SQRT(t(hours)/8742h).For t = 24h you get these ominous 0.42ppm.First, this crude criterion has another flaw. If you have a 4ppm/yr. reference built in, this criterion is two times too high.Second, this usual SQRT law will vanish after some years, and instead effects like popcorn noise, or random walk effects will get dominant.So the drift of such references will probably never come to an end.For comparison, I show the timely drift of one of my LTZ1000 references (at 50°C), from 'First Light' to the actual status.The measurement is done relative to the group of the other 7 references, using the 3458A only for comparing them.So this measurement is an approximation only for the absolute timely drift, but supported by several baseline comparisons to calibrated standards (e.g. on MM2019).The comparison is done on a monthly basis, so you see a lot of small jumps and humps on the order of 0.2ppm.These are caused by the intermittent measurements, maybe also by other drift phenomenons.In the end, this is my worst drifting reference.. if hp would implement the LTZ1000 as intended, i.e. at 50..60°C oven temperature only, for metrology purposes in a metrology grade environment, an annual drift rate of typically -0.8ppm/year could easily be achieved.To demonstrate that such stability measurements can also be performed much smoother, I also show a continuous 24h experiment, comparing my 3458A versus an ultrastable Datron 7000 reference at constant room temperature (after 2h). There's no ACAL during these 24h. A combined noise of about 280nVeff, and small random jumps of +/- 0.1ppm can be observed. Both effects are caused mostly by the LTZ1000 / LTZ1000A references inside both instruments.In the end, these are practical and realistic use cases for the 3458A, showing the general limitations of DCV stability measurements.Another hint, my 3458A obviously does its job nicely, as no practical relevant drift of its U180 can be detected in this case.Looking at these diagrams, this discussion, whether the theoretical 0.03ppm/day drift for the U180 of MiDi's 3458A, is' healthy', or not, to me seems to be really academic.Frank

author: dietert1
author_rank: Super Contributor
timestamp: July 26, 2020, 09:13:34 am
content: You need to understand that the square root formula is a characteristic of random walk. I expected a physicist to know that ("Braunsche Bewegung"). When you read the technical note linked by Midi, it is completely clear that the authors are treating ADC drift as random walk and they could not imagine that an ADC will exhibit a continuous and persistent 11 ppm/year drift. The 8 ppm/year or 4 ppm/year instrument spec is exceeded at a continuous drift of 0.03 ppm/day as observed by Midi. I know this drift can be hidden by the ACAL procedure, as long as it works.Seems like you want to divert the discussion away from Midis findings about the 3458A ADC to your favorite LTZ1000 hobby. But the question of ADC drift is different from the question of voltage reference drift. It is not academic, because the most sophisticated and linear ADC is useless once it does not work. With a voltage reference, we know how to fix that. If you want to contribute something useful, you can provide a log of ACAL 72 drift of your instrument, so we can see if it is nothing or 0.03 ppm/day.

author: ap
author_rank: Frequent Contributor
timestamp: July 26, 2020, 10:35:24 am
content: Hi Frank,I stick to the 0.43 ppm spec, measured over the time specified (ok, when there is no drift after say 4 days, one can also stop there, provided stable ambient temperature). I check the meters continuously against a set of references (732s/4910), so no ACAL needed to determine the drift. Making an ACAL-based drift test every day does not supply meaningfull data imo (and as per spec).When working with a 3458A, it is not about personal feelings or so, the instrument needs to meet its spec. The 0.43ppm is the only spec related to the A/D. That being said, a meter showing 0.4ppm/day (and I have not seen that) would be considered bad, altough well usable. You either have a drift of some ppms/day if bad (seen up to 20ppm/day), or in the 0.1ppm/day and below range if good (all averaged over the specified time).For me the value of the 3458A is not to try to achieve sub ppm measurement uncertainties, even with a 2ppm/a low drift version (and most aged instruments today are in that range anway), if I need tight uncertainty I always use the meter in transfer mode. Thats most of the measurements when working with high accuracy stuff.

author: Villain
author_rank: Regular Contributor
timestamp: July 26, 2020, 10:45:50 am
content: Quote from: dietert1 on July 26, 2020, 09:13:34 amI really enjoy the discussion here and i am happy lurking but i gotta correct this real quick as we want to pay tribute to the great people before us correctly. Its Brownsche Bewegung not Braunsche.

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 26, 2020, 11:22:42 am
content: Quote from: dietert1 on July 26, 2020, 09:13:34 amDear Dieter,Random Walk obviously is understood as a drift in random directions, like up /down/left right, like the Brownian Motion, to designate it correctly.The initial drift of a voltage reference shows no random, but a definite direction, i.e. for the LTZ1000 in most cases always in the negative direction.So you probably have something different in mind.I already contributed my CAL?72 stability data years ago, in another thread, and just again inside this 24h stability measurement, just in front of your nose.You can easily estimate the max. 24h drift of U180 from that, it's well below these 0.43ppm/24h.Please also verify your ideas about drift and ACAL of the 3458A against the recent statements of Adrian.But anyhow, as you now finally are getting personal:'I expected a physicist to know..'and'..want to contribute something useful..', it's now evident for me, and what I supposed the whole time reading your comments, that you just try to play bullshit bingo, here and in other threads.To follow the saying 'Don't feed the Troll', I will neither consider, nor answer any of your statements any more.best regards Frank

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 26, 2020, 11:24:44 am
content: Quote from: ap on July 26, 2020, 10:35:24 amAdrian, thank you very much for these quantitative explanations.Seem to agree with mineFrank

author: dietert1
author_rank: Super Contributor
timestamp: July 26, 2020, 04:03:53 pm
content: Amazing how engineers have difficulties with this. How can one say the limit is 0,43 ppm/day? If that was a continuous drift, after a year that would amount to about 157 ppm and technically speaking that ADC is junk. Such drift would be a clear indication that something is wrong.Quote from: TiN on April 15, 2020, 10:25:00 pmIf a potential buyer sees an ADC drift of 20 ppm on the first day or for some days, that case is simple. Maybe if he sees a total of 20 ppm drift after a week, after a month or after a year the conclusion should be the same. Apparently judging the state of a 3458A requires some patience.Regards, Dieter

author: Villain
author_rank: Regular Contributor
timestamp: July 26, 2020, 04:22:08 pm
content: I feel like what you are saying dieter is that "a unit is drifting lets say 0.4 ppm/day which is roughly 150 ppm a year which is out of spec". That is the feeling i am getting here. But this is simply not the case because ACAL will take care of that and compensate for this drift (if something really is broken with the unit even ACAL will not be able to compensate and probably fail, then you send in your unit for repair, its quite simple). Specifications are only valid with last ACAL within 24 hrs and +-1 degree of current TEMP?. This will keep the unit well within spec. I am not saying that 0.43ppm/day is good, but the unit is fully working because it performs to its specifications and + does not violate the service note referred to here. That many people in the metrology section have tighter specifications or expectations in mind regarding to 3458A has nothing to do with the unit being broken if our expectations are not met.I feel like i do not understand the point you are trying to make here (and i am not saying that is your fault, maybe i personally can just not grasp it right now)I am not saying drift issue of 3458A is "no issue", i am just saying that a unit drifting 0.3ppm/day 0.4ppm/day is not necessarily broken.If your point is that many units have U180 drift issues and you want to say "how can you buy such a product" then just don't buy it no one forces you to.edit 150 per year obviously yes dieter, does not change my answer though

author: dietert1
author_rank: Super Contributor
timestamp: July 26, 2020, 08:22:57 pm
content: No, 0.43 ppm/day of continuous drift translates into 157 ppm/year, not 15 ppm/year. Yes, ACAL may take care of that. With some luck, because an ADC that drifts that much, may have other problems, too. Bad resistor tracking of a thin film resistor array can not explain more than 100 ppm drift.https://www.eevblog.com/forum/repair/agilent-3458a-repair-232680/msg3017320/#msg3017320I found a CAL 72 log that user franklin posted in another thread in April and put his data into a diagram. There is no continuous drift but something like noise (probably temperature related). That log extends over one month and 30 days * 0.03 ppm/day = 0,9 ppm, that's definitely excluded.Regards, Dieter

author: TiN
author_rank: Super Contributor
timestamp: July 26, 2020, 10:45:24 pm
content: QuoteThis!I use 3458's for days and days without ACAL, so 0.1ppm/day drift would drive me mad. That's a reason why I hunted down golden ADCs and polished instruments until they don't show any drift (just random noise/walk jumps) in days terms and don't have any tempco for DCV. Hence requirements are far tighter vs manufacturers spec. Obviously, I also monitor ADC constants on every ACAL between experiments to keep confidence that it's still all happy.And A3 with large resistor ratio issues also have other problems which nobody talks about, other than ominous drift that's not very important to actual practical work

author: Villain
author_rank: Regular Contributor
timestamp: July 26, 2020, 10:49:05 pm
content: Quote from: dietert1 on July 26, 2020, 08:22:57 pmYes was typing to fast, forgot one zero there. Does not change my answer though.Quote from: TiN on July 26, 2020, 10:45:24 pmThats very impressive performance TiN!

author: maat
author_rank: Regular Contributor
timestamp: July 27, 2020, 12:18:44 am
content: Quote from: Villain on July 26, 2020, 04:22:08 pmI believe what dietert1 is saying, is, that a 3458A showing 0.03 ppm/day linear drift is living on borrowed time. It can be brought back into spec using ACAL every day, but sooner or later that ADC will die and will have to be replaced. If you have a spare device and running on warranty - not a big deal if you use the device in a lab.Since the 3458A is running 24/7 on assembly lines and test setups all around the word and there is not much off an outcry, I do believe the issue is not that big. I would rather assume that the devices on Ebay do show a tendency for failing ADCs. My ADC died as well and before doing so it also developed a horrid tempco of about 0.85 ppm/K (https://www.eevblog.com/forum/metrology/hp-3458a-ad-board-spare-part-availibilty-and-cost/msg3001606/#msg3001606). (Note: I do not know if the tempco was there before. I saw the drift first, then dug into the matter.) So there might be even more problems coming along with the drift, resulting in the device ending up on Ebay.Back to dieters point: A lot of people on this forum bought their unit on Ebay and if their ADC is showing drift, they should be prepared to put down another 1.5k to have the board replaced by KS. So sum it up, I guess dieters point is not so much about the device not performing to spec, but rather about protecting one's investment.

author: Villain
author_rank: Regular Contributor
timestamp: July 27, 2020, 02:59:57 am
content: Quote from: maat on July 27, 2020, 12:18:44 amWell, i agree that for sure you have to be careful where/from whom to buy your 3458A. Or just buy a random one and put money on top for possibly new A3 board etc.

author: martinr33
author_rank: Frequent Contributor
timestamp: July 27, 2020, 05:00:05 am
content: But that was in the days when you could get a replacement A3 board.On the subject of drift, the ADC board is not really part of the specification because of the 24-hour autocal requirement, which can mask a lot of drift.I say that becuase all of the 3458A accuracy specifications require an autocal within 24 hours before the reading.The ADC board would have to be truly horrible to drift by enough to be outside of the 2.6ppm post 24 hour specification.It is only when watching precise references, without autocal, over a long period that you start to see these errors.Also - whan a 3458a is sitting in a semiconductor test rack, I suspect it is using its other skill - super fast lower resolution measurements. The ADC errors won't show up there.

author: e61_phil
author_rank: Frequent Contributor
timestamp: July 27, 2020, 06:12:30 am
content: Quote from: martinr33 on July 27, 2020, 05:00:05 amThat is also what I think. Most people wouldn't even notice an ADC problem. They will run ACAL before use and everything will stay very well within the 8ppm specification (and a 3458A can do much more than 10V measurements and for the other ranges the ADC drift is even less important). Therefore, I doubt that most 3458As are on eBaybecauseof a drifting ADC. And I also doubt that there was a bad batch in 2006. I saw that problem on much older 3458As.For me it looks like that problem isn't that unusual and is spread over all 3458A generations. Imho that would also fit to the findings of TiN and ap.Quote from: martinr33 on July 27, 2020, 05:00:05 amIf the new A3 board is really 100% compatible, and it sounds like it is, I would guess you can buy new boards for your old instrument soon.Best regardsPhilipp

author: Kleinstein
author_rank: Super Contributor
timestamp: July 27, 2020, 11:22:02 am
content: Quote from: e61_phil on July 27, 2020, 06:12:30 amThe drift is only the first visible symptom of a failing U180. Changes are a drifty ADC will after not so long time (e.g. a year) show error messages about ADC convergence. The faster conversions are actually more sensitive to the resistor ratios - so DNL errors may be become visible too. I would not be surprised if this would be earlier with the fast modes than with the higher PLC modes.The reports are that keysight is currently not selling individual A3 boards, but just replace it as part of a repair. This could be to check for possible compatibility issues with older / mixed units. For serious use of the 3458 one would need a new CAL after the ADC board replacement anyway. So sending in the meter for repair is not that much extra hassle for most customers.

author: martinr33
author_rank: Frequent Contributor
timestamp: July 27, 2020, 12:02:48 pm
content: My observation - based on a limited sample - is that there are three classes of drift:- very stable, close to 0 ppm- low drift, in spec but clearly observable- high drift, out of specI am thinking, based on your comments, that there is a fourth class, where drift accelerates out of control. I've not seen that, yet, and my drifting unit was 25 years old and well outside of the block of units described in the Agilent note.I wonder if the convergence issue end state is confined to that block of serial numbers.Also, even a unit with minimal drift can deliver a convergence error if it is never autocal'd.

author: notfaded1
author_rank: Frequent Contributor
timestamp: July 27, 2020, 12:11:22 pm
content: I'd be curious to know what a new A3 with CAL from Keysight would cost? I'm guessing it's not a normal hobbiest fee? At least when they sold A3 boards you could buy one put it in and then work a hobbiest CAL with some help from other voltnuts or against your own 10V references and 10K Ohm reference.Bill

author: maat
author_rank: Regular Contributor
timestamp: July 27, 2020, 01:11:54 pm
content: Quote from: notfaded1 on July 27, 2020, 12:11:22 pmLast time (2019) I sent in my 3458A for cal, it is was around 700 €, but I took a deal including an additional year of extended warranty for a bit over 800 €. Replacing parts incurs a fee of about 300 € on top of the part cost (1.5k - 2k for an A3 board). In my opinion sending in the deviceandtaking the warranty extension, which is about 112 €/a is the real deal you can make here, because it will give you the peace of mind, that your little baby will happily live ever after.Given the fact, that KS collects and returns your device, all in all their service is not that expensive.

author: martinr33
author_rank: Frequent Contributor
timestamp: July 27, 2020, 06:45:49 pm
content: Yes - I think this is one of the things that keeps complete but broken units expensive. Keysight has (had?) that $2700 deal that includes cal and full refurb. So a $3k ebay junker + $2700 gets you a fully refreshed and warrantiable unit.It is quite possible that they will not make the A3 board available, as other parts have also disappeared. The world has moved on from self-maintenance of instruments.

author: dietert1
author_rank: Super Contributor
timestamp: July 27, 2020, 09:07:16 pm
content: Even at that expense they might give you a unit with a drifty ADC and call it "in cal". As far as i understand the official ADC drift limit would be +/- 0.43 ppm/day. And do they borrow you a spare during maintenance? So probably you will end up buying several units.When buying a pre-owned instrument i would try to get an agreement on a two week test period, like somebody recommended above. The ACAL 72 log of franklin i linked above was in fact only two weeks and it seems to be enough to take a decision, unless you have a "borderline" case like Midi's. And of course i would clean the fan filter, like Midi recommended and also put IC coolers onto those hot comparators. If cleaning the fan filter makes a difference, IC coolers will probably make one, too.Regards, Dieter

author: e61_phil
author_rank: Frequent Contributor
timestamp: July 28, 2020, 08:55:23 am
content: Quote from: Kleinstein on July 27, 2020, 11:22:02 amI saw 3458As which have a drifting A3 Board and run more than a year with that problem without showing convergence errors or something like that. Even if you send them to calibration no one will notice that. I also doubt, that many people will notice an increased DNL.If the ADC really develop such problems, it makes the 3458A an unreliable transfer machine. I know many people who are using the 3458A as a ratio machine only and never calibrate it in a traditional way (which wouldn't help). They use it in a single range and measure FS and 0 before a measurement. And I'm sure they aren't looking at CAL72 values.I hope an ADC which is getting worse in linearity will show that drift, otherwise it is really hard to make sure that your measurements have the uncertainty you expect.

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 28, 2020, 10:06:05 am
content: Quote from: Kleinstein on July 27, 2020, 11:22:02 amKleinstein,these are very severe assumptions. If these were really true, that would mean that the technology used in the 3458A would not work correctly after some time, affecting then 100% of all instruments.Please provide proofs for your statements, best from your own experience / instruments, otherwise please give a precise citation where these claimed effects have been observed by others, i.e. here in the forum, or on other platforms.I do not remember at the moment, that anybody has seen or proven such additional malfunctions in conjunction with a failing U180Thanks.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 28, 2020, 12:46:16 pm
content: The good DNL needs a good resistor ration for the fast and slow slope. The faster case supposedly need the critical resistor ratio to be good for some 0.1 %. This is normally not critical for a good resistor array. However with a broken chip and dirfty unit (e.g. TiN had some 4 ppm per day), this 0.1% accuracy may no longer hold. A just borderline unit with 0.4 ppm / day drift would not reach a significant error. The DNL relies on a different ratio - so there is no direct relation saying up to 500 or 1000 ppm total gain drift would be OK.Depending on the direction of the drift the convergence error may happen (as a waring) or not.One would hardly notice DNL errors in the slow modes, unless it would happen to be just at zero and cause higher noise. The slow mode is also less sensitive. At the high speed a step from, 4.5 digit to 3.5 digit performance may be more obvious and it needs less resistor drift.Ideally the self test and even the normal power one self-test could check for the resistor ratios at the ADC. This would be directly the fast / slow slope ratio and not the gain drift. However POS is not run with a unit that runs 24/7. As the software is from the good old times chances are they may do the check, but I don't know. Today is should be a requirement - but SW quality is more and more diluted with increasing code length. Testing on power up would be still tricky as the meter is not warmed up naturally. I don't know how much self test is included with ACAL - ideally it should do some quick tests too.Even if just used as a ratio instrument one should still run some checks - the self test on a regular basis (e.g. every 6 months) would be the minimum. Ideally this should include checking the ADC gain (CAL72 value) for the SN18 drift, as a drifty ADC is a known possible mode of failure.

author: dietert1
author_rank: Super Contributor
timestamp: July 29, 2020, 09:09:01 am
content: When researching the web about "3458A U180" i could not find anything from Agilent mentioning quality problems or resistor array drift, except the basic design considerations that Kleinstein repeated.The only one who really worked on the problem and dared to unsolder U180 hybrids from ADC boards was Tin. He tried to understand the problem better, but did not arrive at a definitive conclusion about what is the typical problem inside a bad U180. I can't understand how a thin film resistor array would cause a tracking drift of several ppm/day.Concerning firmware quality: Tin described somewhere how to recover a 3458A from a condition where no more calibration can be completed after a previous calibration put the instrument to far off the track. So it's a complicated machine and there might even be a software bug causing calibration to drift or fail on certain drift patterns (for no real reason). But that's speculation again.Regards, Dieter

author: chekhov
author_rank: Regular Contributor
timestamp: July 29, 2020, 10:54:26 am
content: Out of curiosity I've looked into original HP journal dedicated to 3458A design, and resistor network might be not the only thing that this ASIC contains:QuoteThus, If I'm reading it right, not resistor may fall but switches.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 29, 2020, 02:03:02 pm
content: The main part of the resistance is due to the resistor and only a small fraction (e.g. 0.1% range or less) is due to the switches. AFAIK HP did not even confirm that the drift is due to U180.In theory drift of the fets could also lead to gain driftTiN's measurements did shown that U180 was at fault and they also showed that the reference voltage scaling to +-12 V did drift quite a bit. This part does not include any switches, just 4 resistors from the array.It is unusual to find such massive drift in a resistor array, but drift already with the scaling part is essentially limited to the resistor part. It also looks that the effect is not just with a few resistors, but more like effecting all resistors to a varying degree. My best guess would be something like breach of hermetic seal or maybe decomposition of the glue that would release corrosive gas or maybe just the glue coming loose and release of mechanical stress.

author: Grandchuck
author_rank: Super Contributor
timestamp: July 29, 2020, 04:46:55 pm
content: My 3458A is in mint condition. It had been advertised as never used. Upon receiving it, all original parts and packaging were present. Not one mark, ding, scratch, or dust in the filter. But, it seems to fall short of the "golden units" described by TiN and others on the forum.My voltnuttery has led to the construction/purchase of four LTZ1000 references. It would seem they are noticeably better than the DMM. A spreadsheet and graph are included below.The DMM uncertainty (36.4 uV @ 10V) is specified in the calibration report that was part of the package. The meter is branded Agilent and the date of manufacture is 2011.

author: TiN
author_rank: Super Contributor
timestamp: July 30, 2020, 02:03:32 am
content: QuoteI did arrive to definitive conclusion, but I thought it's obvious enough already and didn't feel repeating it. If one cares for meter to meet spec, SN18 is official as it gets. If one wants better than specs, well, you are on your own hunt for magical 0.0ppm/yr system.Feeling like every year people here refresh and have this kind thread about u180, repeating same things over. I remember Dr.Frank explained these same things at least 3 times by now.

author: dietert1
author_rank: Super Contributor
timestamp: July 30, 2020, 06:37:40 am
content: We have been using HP 3456A for years and years. Those don't have that ACAL procedure to check the ADC, so all ADC deviations enter as errors into the measurement. The ADC has to be very stable and it is (except some small temperature coefficient). Long term stability is something like +/- 1 or 2 ppm per year. Our instruments are old and well aged.Reading this forum one may get the impression that a 3458A is a must-have for metrology, because it's ADC has the best linearity. But then we read that its ADC contains a part that may cause tremendous drifts. Drifts up to 157 ppm/year are officially considered "normal", as long as the ACAL procedure takes care. So in my eyes the 3458A series is a similar kind of retarded progress as the 3457A series. Just think about the fan that came back after it vanished from the 3456A and the 3457A.I think people are asking over and over again, because all this is hard to believe and difficult to understand. What i take from this discussion is that a metrology grade 3458A is something special that money won't buy. Maybe that's the reason why people try to be friendly with Agilent/Keysight.Regards, Dieter

author: The Soulman
author_rank: Super Contributor
timestamp: July 30, 2020, 08:24:57 am
content: Quote from: Grandchuck on July 29, 2020, 04:46:55 pmWhat is the timing interval of those measurements?Did you use autocal prior to each measurement?

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 30, 2020, 08:26:37 am
content: Quote from: TiN on July 30, 2020, 02:03:32 amIllya,thank you for your explanations, setting the discussion about drift parameters of the 3458A to the correct, practical perspective.I hope that this will finally calm down some owners of a 3458A, who were made nervous by several theorists here - sorry I can't call them otherwise.Latter, who even compare a 6 1/2 digit DMM to the 3458A in terms of stability or alike, thus obviously demonstrating that they did not even understand principle and specification, I really can not take serious any more.Frank

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 30, 2020, 08:39:16 am
content: Quote from: Grandchuck on July 29, 2020, 04:46:55 pmHi GrandchuckIt's not clear, under which conditions you made your measurements, i.e. NPLC setting, temperature stability of room / 3458A, frequency of measurement..I have just recently published such stability measurement of a 3458A vs. LTZ1000 reference (or similar).+/- 0.1ppm over 24h, 200nV short time noise shall be achieved for healthy devices.Maybe you try to make a similar measurement.From your data, I can't realize how you can state that your 3458A does not perform as well as the LTZ1000 reference.Frank

author: The Soulman
author_rank: Super Contributor
timestamp: July 30, 2020, 08:43:16 am
content: Quote from: dietert1 on July 30, 2020, 06:37:40 amIn my mind the 3458a ADC had the following design goals:*high resolution/dynamic range*excellent linearity*high speedAnd with those three things combined there was no room for:*long term stability*low power consumption/low temperature*low cost*numerous other thingsThe long term stability has been "solved" by using autocal frequently, that is what it is there for.

author: The Soulman
author_rank: Super Contributor
timestamp: July 30, 2020, 09:33:49 am
content: From the manual:Quote

author: Grandchuck
author_rank: Super Contributor
timestamp: July 30, 2020, 11:41:30 am
content: More information about my measurements:1/ NPLC 1002/ Readings taken every 24 hours3/ DMM warmed up at least 4 hours before each reading4/ DMM turned off each day5/ Autocal performed immediately before each session6/ Lab is temperature and humidity controlled (plus/minus 1 degree C)Thanks Soulman and Dr. Frank!My conclusion is that the DMM internal reference is moving a bit ... perhaps due to the on/off cycling. The external LTZs are powered constantly. Autocal shows little to no change. That would indicate that the A/D board is solid?TiN, how is "superstable" LTZ1000 reference project coming along?

author: Villain
author_rank: Regular Contributor
timestamp: July 30, 2020, 01:50:37 pm
content: Quote from: Grandchuck on July 30, 2020, 11:41:30 amI know for some this sounds stupid but when i hear someone saying "turning off 3458A each day" my stomach twists and turns.

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 30, 2020, 02:18:30 pm
content: Quote from: Grandchuck on July 30, 2020, 11:41:30 amYes, measuring once a day, but shutting off in between is not the best method.Anyhow if you 're using the 3458A intermittently, like on a monthly basis, like here:https://www.eevblog.com/forum/metrology/hp-3458a-ad-board-spare-part-availibilty-and-cost/msg3156428/#msg3156428Then these fluctuations should be 1/10 of yours only, i.e. +/- 0.2ppm from day to day. Especially this common dip +2ppm at day 6 makes me wonder, what's going on.You also need to take each measurement with sufficient statistics, i.e. with standard deviation, so you can see if something is fishy.Personally, I take 16 readings @ NPLC 100, with statistics, for each reference and for a single measurement point.If the StD of 3458A vs. LTZ1000 is from 100nV to 300nV, then the measurement is ok.You should also check if your used cable is ok, i.e. low thermal gold plated or pure copper. This can be checked by reversing the cables at the DUT and comparing if + and - measurement are identical to about or below 1µV.I would also recommend, to do a 24h stability monitoring , 3458A vs one of your LTZ1000, and with TEMP? monitoring, whether you get such stable curves like mine.From that you can very often deduce, what's wrong.Frank

author: Grandchuck
author_rank: Super Contributor
timestamp: August 22, 2020, 05:19:16 pm
content: Thanks Dr. Frank. The 3458A has been on continuously for a week and things are looking better.So, this is an instrument that should not be turned off when seeking best metrological performance ... makes sense, I suppose

author: rodpp
author_rank: Frequent Contributor
timestamp: August 22, 2020, 05:43:49 pm
content: Any news about the @TiN review of the 3458A Black?

author: e61_phil
author_rank: Frequent Contributor
timestamp: August 22, 2020, 05:48:56 pm
content: Quote from: Grandchuck on August 22, 2020, 05:19:16 pmOur local cal lab told me exactly that recently.

author: niner_007
author_rank: Frequent Contributor
timestamp: August 24, 2020, 12:56:13 am
content: Quote from: Grandchuck on August 22, 2020, 05:19:16 pmIt’s not just the 3458A, any instrument subjected to drifts should be kept on, which is every instrument out there

author: Kleinstein
author_rank: Super Contributor
timestamp: August 24, 2020, 06:46:46 am
content: Quote from: niner_007 on August 24, 2020, 12:56:13 amIt depends on the instrument: some parts that get quite hot in normal operation may show faster drifting and aging when on. This can be the LM399 reference or parts in RF gear that also run at relatively high power density. There it is a balance between the aging and thermal hysteresis effects from a changing temperature. Having an instrument constantly powered also makes it easier to correct for drift, as the drift rate is more predictable.The 3458 is better of running 24/7, though the power consumption is quite high. I am afraid the new black edition (and thus new boards) is not much lower in consumption (mainly the digital part may save a little.

author: dietert1
author_rank: Super Contributor
timestamp: August 24, 2020, 09:39:44 am
content: I think some people here try to use an instrument beyond its limits. A 3458A DVM lhat needs to be kept running 24/7 and needs to be kept at 23 +/- 1 °C and yet needs to be calibrated once a day is definitely used beyond its limits. It may be fun to try and work like that, but not very practical in terms of results. And Kleinstein mentioned it before: Power consumption is more than what is practical with batteries.Regards, Dieter

author: notfaded1
author_rank: Frequent Contributor
timestamp: August 24, 2020, 01:28:43 pm
content: I'm not so worried about the power consumption but more interested in the instruments stable state. Something as sensitive as the 3458 seems to need some real time to "settle" into its most stable state if it's running correctly. On one hand I feel like I might be using up my 3458's life but on the other I know this is it's stable state after running for a few months non stop and I can characterize it's base running capabilities without wondering if it's still going through a recovery from being turned off for an extended period. In many ways it's similar to the way an OCXO needs time to become frequency stable (as much as it ever will be) after being turned off and it's oven cold... maybe a simple analogy but that's how I like to think of it.Bill

author: Dr. Frank
author_rank: Super Contributor
timestamp: August 25, 2020, 12:24:01 pm
content: Quote from: notfaded1 on August 24, 2020, 01:28:43 pmBill,the 3458A generally reaches its stable state (i.e. its specification limits) after a 2..4h warm up phase, with constant room temperature and an ACAL. There is no further settling time like an OCXO always shows.Only if you make observations beyond (below) its specification limits, then you might observe subtle relaxation / hysteresis effects.Practically speaking, when I let my 3458A settle longer, maybe 12h over night before making measurements, one can observe the last tenths of ppm drift, mainly caused by better stabilization of the temperature of the instrument or the room.The question arises, what is really relevant for you, and which quantitative limits you are able to observe.These limits you should define for your use case initially.Also keep in mind, that running 24/7, the old version really consumes the lifetime of these EL2018 comparators, because they were getting quite hot, which is not the case any more with the Black Edition.The inner temperature of the B.E. rises about 5°C less than the old version, due to use of modern components.Let me illustrate this problem a bit deeper with several examples from practical experiences.Remember, that no DMM is accepted as a reference standard (for Volt, Ohm) by any Standards Institute, even if Fluke or HP have once promoted the 8508A or the 3458A as metrology grade instruments.Reason maybe that their internal references drift too much in comparison to pure DCV and Ohm standards.The 3458A is used for metrology purposes at Standards Institutes as a Transfer Standard mostly, using its ultralinear A/D of < 0.02ppm INL, and they let it also run 24/7 to avoid the warm up and stabilization time of 2..4h.Of course these 0.02ppm INL are not officially specified, but they were able to characterize each of their instruments, to achieve much lower specification limits, maybe including timely and temperature stability of the LTZ1000A reference and of the A/D.Like the Standards Institutes, us volt-nuts may also be able to characterize and use the 3458 beyond (below) its specification limits, see TiNs efforts and measurements on his "Golden" DMMs, with near zero ppm drifts, and proven 0.02ppm INL.My 3458A, with an oven set to 65..70°C and intermittently used, shows a DCV drift of only 1.8ppm over 7 years.I'm comparing my continuously running LTZ references (and my VHP202 resistors) once a month, and the achieved repeatability, provided by the 3458A, is on the order of 0.2ppm only. If it would be powered 24/7, I would not expect better numbers, which are already below the limits of what the specification delivers.In contrast, crucial was the recent use of low thermal PTFE cables with reversed measurements, which obviously improved this repeatability.I observed greater shifts up to 0.5ppm, reversible and non-reversible ones, when either the 3458A, or the references were physically transported.Otherwise, judging from these limits, I could not observe any further instability disadvantages, or hysteresis effects by intermittent operation, which you might have suspected.You should define for yourself, which metrological drift / stability parameters are relevant for your, by defining quantitative limits.Then you should perform a reality check, if these limits are really affected by intermittent operation, I doubt that, and what your own capabilities are concerning stability figures.I mean, if you expect e.g. 0.1ppm stability for a specific parameter, and you were not able to check that, or your other equipment is much less stable, what would be the benefit?The 3458As (sub ppm) stability, on 24/7 or intermittent operation, in the end will always play a minor role only, I assume.Frank

author: martinr33
author_rank: Frequent Contributor
timestamp: September 05, 2020, 06:43:25 pm
content: I spent some time poking through the 3458A parts list on Keysight's store, to see if anything might have shaken loose on the A3.There's this piece of text on the new and refurbished board pages:"This part is not available for direct sale but an instrument repair is orderable through our service center. Please contact Keysight to inquire about returning your instrument for repair."https://www.keysight.com/my/partDetail/03458-66523https://www.keysight.com/my/partDetail/03458-69503So this looks like a permanent situation.Also, the Keysight full refurb is now $3099.https://service.keysight.com/infoline/public/product-service.aspx?laf=mya&pn=3458A&lc=eng&cc=US

author: notfaded1
author_rank: Frequent Contributor
timestamp: September 08, 2020, 05:49:29 pm
content: Wow if you want your 3458A compared to the Primary Standards Lab Calibration (Josephson Junction) - Per Incident US$ 2140.00I guess it doesn't get better than that. It's really too bad they won't even sell you an A3 if you want to buy one anymore like most other parts if they have them in stock.Bill

author: Grandchuck
author_rank: Super Contributor
timestamp: September 08, 2020, 06:31:42 pm
content: Bill, to me the absolute calibration is not as interesting as the stability (repeatability) of the measurements that I can obtain. I joined the US Cal Club to see how close my meter is to what TiN and cellularmitosis have prepared. In fact, I might just use that stuff to calibrate my 10 year old 3458AAs a hobbyist, that should suffice. I doubt that I will ever have a truly professional use that demands traceability. If I would, I would pony up the money (not over 2k, though)

author: notfaded1
author_rank: Frequent Contributor
timestamp: September 08, 2020, 07:31:55 pm
content: It's interesting to see what it costs to get your meter calibrated to the Josephson Junction array though! We don't pay for this for our meters at work. Much of ours is done by a company called SIMCO.

author: martinr33
author_rank: Frequent Contributor
timestamp: January 28, 2021, 12:28:12 am
content: Just poking through the Keysight spare parts list again, most PCBs are now unavailable except for a handful of power supplies, the reference boards, and the F/R switch.The new A/D board is at least priced (at $2232), but marked "available until gone". So maybe it will make a comeback.

author: IanJ
author_rank: Unknown
timestamp: January 28, 2021, 08:00:47 pm
content: Quote from: martinr33 on January 28, 2021, 12:28:12 amI bought the F/R switch from Keysight after a Cal at Keysight they mentioned it gave them some possible instability.....so I bought the switch and fitted 1-year later just prior to the next Cal with Keysight.I presume the switch is not bespoke to Keysight and is possibly available elsewhere......else, worth picking one up from them.I also have one of the Ebay sourced Chinese supplied 3458A VFD's in a box, albeit I don't know how good they are.Ian.

author: TheSteve
author_rank: Unknown
timestamp: January 28, 2021, 08:39:49 pm
content: Quote from: IanJ on January 28, 2021, 08:00:47 pmThey used to sell just the switch, now you need to buy the switch PCB assembly.I get the feeling soon there will be almost no parts sold for any product.

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: February 20, 2021, 10:50:16 am
content: Hello folks - I recently contacted a knowledgeable person inside US Keysight organisation.Keysight decided to change its service policy for all PCB sub-assembly products ("replacement boards") -not only for 3458A ... - but for all their standard metrology gear (with a few exceptions for high profile customers).The new policy is that one needs to return unit for $.$$$ repair at "standard service cost".I believe that Keysight PLM should make an exception for this unique instrument and the only way is that the owner's community generates enough noise to make Keysight PLM aware that they took wrong decision.No one will return his unit to KS service center to swap his VFD display for about +3000 USD - it is a foolish decision by KS management and we should convince them to make an exception for this 3458A legacy instrument. If KS management really believes people will pay +3000 USD to service their instrument then their product managers are living on another planet ... - it looks like they want to destroy their own DMM business unit. People who turn their back to invest in high end Fluke (metrology) gear will probably not return as KS customer first two decades ...Herzlichen Grüßen/Meilleures salutations/Best regards/Un saludoBest regardsScoobyDoo

author: HighVoltage
author_rank: Super Contributor
timestamp: February 20, 2021, 11:27:36 am
content: Thanks for the insight of Keysight!No surprise here, this has been the trend at Keysight for a long time.I think we can be happy that we could buy so many parts all these years.Look at Keithley for instance, you can not get any internal parts for anyof their instruments and this has been like this for 10 years already.

author: branadic
author_rank: Super Contributor
timestamp: February 20, 2021, 11:48:06 am
content: That is as silly as having the meter calibrated at Loveland and then transported via airplane back to original continent, while the meter is sitting in the back of the plane with temperatures as cold as ...Would sometime help if managers would use the thing between their ears instead of smelling the fast dollar.-branadic-

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: February 20, 2021, 02:45:49 pm
content: Hello Folks - Keysight recently created an update of their 3458A Assembly level & repair manual (03458-90018)https://literature.cdn.keysight.com/litweb/pdf/03458-90018.pdf?id=3092042However I am asking myself the question which purpose this has as current owners have no access to the replacement boards - we all have to return unit to KS service centre and pay +3000 USD - what a joke ...Is it politically incorrect to make statement that Keysight is misleading future customers with making this manual publicly available if these customers have no access to these boards and need to pass KS service centre and pony up +3000 USD ... - what an 1st April fools joke it looks like ... (?)Herzlichen Grüßen/Meilleures salutations/Best regards/Un saludoScoobyDoo

author: dietert1
author_rank: Super Contributor
timestamp: February 20, 2021, 03:50:03 pm
content: If you read page 101 of the document, the words are "Keysight can .. ", not "Keysight will ..". I haven't seen the numbers but probably they are suffering a lot from the Chinese taking away more and more of their global business. And maybe they are trying to focus on national business, where guarding IP is a little easier.Regards, Dieter

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: February 20, 2021, 04:26:32 pm
content: Hello Folks - the standard service cost at Fluke for their Metrology gear (F8508A/F8558A/F8588A) is less than 1300 € ... - Keysight charges a fee close to 3000€ "only" ...At the end of the day ... only stability - accuracy - cost and total cost of ownership is what matters most ...Herzlichen Grüßen/Meilleures salutations/Best regards/Un saludoScoobyDoo

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: February 20, 2021, 04:52:09 pm
content: Quote from: dietert1 on February 20, 2021, 03:50:03 pmA1.: Text says in US ... (Lawyers Talk - LoL)A2.: They nursed Rigol (Pudong - Bejing in RPC) ... shot in their own foot and making a new mistake again ...Herzlichen Grüßen/Meilleures salutations/Best regards/Un saludoScoobyDoo

author: Villain
author_rank: Regular Contributor
timestamp: February 20, 2021, 05:25:10 pm
content: Well, lets keep it real. The people in this forum that complain about this situation (rightfully so or not does not really matter) are probably .01% of the customers. The other 99.99% are huge tech companies that just pay the 3k$ because they don't care, especially not the company engineer who needs his 3458A repaired, because the company pays for it, its not his own money.That is the same reason for this "outcry" to be so "quiet" that it will fly under the radar entirely.Again i am not saying that this is right or wrong.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 20, 2021, 05:50:53 pm
content: In countries like the US, GB or Germany it is not so bad to send the meter to KS to repair and get it back relatively fast. Often one would need a new cal with a repair anyway - so one may want to send the meter in anyway even if one would replace the board. However the price looks relatively steep - given that the ADC failure is more like a know issue and likely not user fault. It may make a difference if the repair cost in clude calibration, but I am afraid this may be extra.However in less developed countries with no local KS support, sending a meter out to repair can be major hassle. Also wages may be lower so that a repair, even at component level may be an option. A board swap is relatively easy especially with the relatively modular 3458 a very vialble way.Sometimes speed may be more of an issue than costs - sending out just the board is natural half the time for shipping, and less risc of damage during transport. This also applies to more normal customers, unless next door to KS service center. Not all customers need a cal certificate - though a new cal after repair is defintely a good idea.

author: saturnin
author_rank: Regular Contributor
timestamp: February 20, 2021, 06:18:55 pm
content: Quote from: ScoobyDoo on February 20, 2021, 04:26:32 pmHmm...just to put it to perspective...fix-price repair of Keithley 2002 incl. traceable standard calibration under ISO9001 is 2’400€ (excl. tax of course) ... the offer is from Dec 2020. I also asked whether they sell a certain spare board, they said no - as I expected.

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 20, 2021, 06:43:06 pm
content: Quote from: saturnin on February 20, 2021, 06:18:55 pmThat's interesting. I send our 8508A this year to Fluke and they charge 1282€ as a fix-price.

author: saturnin
author_rank: Regular Contributor
timestamp: February 20, 2021, 06:52:58 pm
content: It is suspiciously cheap (for Fluke). Does it include a calibration?

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 20, 2021, 07:02:17 pm
content: Quote from: saturnin on February 20, 2021, 06:52:58 pmWas does "for Fluke" mean? My experience is, that the Fluke calibration is not only cheaper (<1k for 8588A and slightly above 1k for 8508A, but ~2k4 for 5730A) than Keysight, but also much lower in uncertainty. All the Fluke calibrarions had <0.5ppm uncertainty for 10V (last 8508A cal 0.43ppm for example). All the Keysight cal sheets I saw were more in the 3ppm range at 10V. Same with the other ranges.But you're right. The 1282€ doesn't include the calibration. Together with the calibration it will end very similar to the Keithley 2002 price.What does that mean for the 3000€ Keysight wants to have? Does it include calibration?

author: saturnin
author_rank: Regular Contributor
timestamp: February 20, 2021, 09:10:53 pm
content: Quote from: e61_phil on February 20, 2021, 07:02:17 pmSorry, I am non-native speaker and used bad expression. I meant that 1282€ is surprisingly low price for 8508A service. I would expect more. As you wrote, you will end up with a similar price when you add calibration costs. I guess 3000€ Keysight service is the same case, otherwise it is really expensive.Thanks for overview of calibration costs for other test gear.

author: niner_007
author_rank: Frequent Contributor
timestamp: February 20, 2021, 09:25:18 pm
content: Quote from: e61_phil on February 20, 2021, 07:02:17 pmI don't know about Europe, but 8588A calibration in US is $2,198.00. That was a quote directly from Fluke. 3458A is cheaper to calibrate, with more options available.

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 20, 2021, 09:37:45 pm
content: Quote from: niner_007 on February 20, 2021, 09:25:18 pmIn germany it is 987€ via CalPlus in the Fluke Cologne Lab for an ISO 17025 DAkkS cal. For most cals there is also a cheaper option without DAkkS certificate.What are the special options Keysight offers?And I have no doubt that there is a difference in the US. As far as I know Keysight has only a JJA in the Loveland lab. They will offer much better uncertainty than 3ppm I guess.

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: February 20, 2021, 09:37:55 pm
content: Hello Folks -at a given moment in time - Rigol will throw out its own affordable 8 1/2 - 9 digit DMM ...It is just a matter of time ...Herzlichen Grüßen/Meilleures salutations/Best regards/Un saludoScoobyDoo

author: niner_007
author_rank: Frequent Contributor
timestamp: February 21, 2021, 12:55:06 am
content: Quote from: ScoobyDoo on February 20, 2021, 09:37:55 pmIt's not just a matter of resolution, it's the accuracy we wantI very much doubt Rigol will put out a metrology instrument

author: Kleinstein
author_rank: Super Contributor
timestamp: February 21, 2021, 09:28:43 am
content: 9 digits is not rellay realistic (unless 210,000,000 counts would be be called more than 8.5 digits) - more like a slightly faster 8 digit meter. The difficult part is the linearity, not noise and the reference part is also limiting on how much resultion can really be used. Even with a perfect reference in the meter it is still the usual DUTs that have there own noise.Rigol likely would not compete for metrological use outside China, but there may be new lower cost instruments in the range of faster 7 digit meters for more industrial use.With the high prices and limited export from the US, there may still be a place for new competition for high end test-gear from China or similar. Rigol already started at higher grade scopes.Service with test gear is a difficult point: the modern instruments got relative robust and do not fail that often anymore, but if they fail, a repair can be really hard, because much is on a single board and highly integrated. A component level repair is thus difficult and also often expensive unless one knows the faults (like common faults). With the high wages in the US and similar countries such a repair fast gets costly. A board swap looks odd which much on one baord - it may still be OK for the manufacturer, as the actual replacemanet board may not that expensive if one does not include the one time developement costs.Repair also usually needs recalibration and maybe even a more detailed testing. So it makes some sense to send back to the manufacturer.With Rigol or Sigilent meter repair is likely also not fun - they have a similar problem and at the lower cost level for the new meter just buying new is even more attractive. Even just a regular calibration can be a hassel.The modular design of the 3458 still allows more repairs than with many other instruments. The display and battery backuped RAMs are kind of natural wear parts. Especially for known failure types like dimm display or the dreaded ADC failure a simple board swap without shipping the hole instrument makes absolute sense.

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: February 21, 2021, 10:02:25 am
content: Hello Kleinstein, folks - good morning,I agree with your post ... - just wanted to trigger the 3458A owners community that KS should keep A3 + A5 + A7 + A9 boards available to end customers as it has been for many years ... and it is good that Fluke is challenging Keysight to further improve the current 3458A - although I doubt that will ever happen ...Since 2017 - the cost of 03458-66513 A/D board has inflated +3 times (300%). If a skilled technician was capable of servicing such unit in past over 3 decades - why would this no longer be possible in future ? There are many universities that own such 3458A but have problems to afford such standard service repair - the modular 3458A was designed for board level repair ...In my case I have access to calibration calibres - so I really see no need to return such instrument to KS for a simple board swap and a calibrationsession to connect unit to a full automated rack and being charged 3000€ ... - we prefer manual calibration on every rangeIt just gives me impression that Keysight's management is only concerned to improve shareholders value and not the quality and service level of their product portfolio ... - I hope I am wrong ...Herzlichen Grüßen/Meilleures salutations/Best regards/Un saludoScoobyDoo

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 21, 2021, 10:13:41 am
content: Hi,for me as a private 3458A owner it is also a pity that KS will stop selling spare boards, but to be honest, I don't thing it will hit so many companies. In most cases it is way more expensive to let an engineer search for the failure than sending everything to KS, let them fix the box and get a working, tested unit with some warranty back.And also for the calibration. I doubt that there are many people who are able to calibrate a 3458A by their own (connecting a known 10V and 10k resistor isn't a calibration). On the other side a calibrated 3458A isn't neccessary in most cases. Due to it's superb linearity and low noise it is a very good transfer standard. Absolute accuracy isn't that important for many metrology applications.

author: martinr33
author_rank: Frequent Contributor
timestamp: February 23, 2021, 04:23:47 am
content: Much of a 3458a is still repairable. The drifty ADC is not. Some of the relays maye be awkward, and replacing them with sub spec parts is a bad practice.I don't know if the CPU PALs are protected or not, but it isn't too hard to dump them out.Displays are available.Even then, a drifty ADC can be hard to spot quicly without a very stable reference. The recommended process to test drift over a period (assuming you don't have a super stable reference) is someting for which few folks have the patience. Even here, I am not sure how many folks have sprung for a new board.And one unit I have - early serial number - drifted like crazy for a few weeks but now seems to have settled down to stable. As in, doesn't seem to be moOne last thing. The 8051 on the ADC board has to be capable of spotting the ADC drift. I wonder if there is some technique that could correct teh meter on the fly. The designers probably did not know that it would be needed.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 23, 2021, 08:03:19 am
content: Checking for ADC drift does not need a stable external reference. The way to test is checking the cal constant from the ACAL call - so no critical voltage referece involved. Even if the internal A9 ref would drift a lot, it would hardly effect the test. However this test needs time, especially if the temperature is not very stable. A doubt that some of the 8051 are not able to detect the drift - this should be a function available in all versions. For critical use of the meter (e.g. in a CAL lab) it should be good practice to regularly check for the ADC dirft, e.g. like recording the ADC gain value like once a month. A meter not regularly used may show some changes in the ADC gain from humidity or similar effects, not directly related.I doubt there could be a simple fix (except exchanging the board or U180) to the ADC drift - a failing U180 can cause more problems than just gain drift. The gain drift is only the point that is easiest to measure. If the error gets larger chances are the ADC would complain with a conversion error. It looks like the problem is inside U180 and an external fix is essentially impossible. One can circumvent the problem from moderate gain drift with a more frequent ACAL call, but this would not fix other problems that can come with a failing U180. A drifting ADC may also show higher DNL errors and chances are it will evenuall stop with an error message. Chances are high that when the convergence errors start to pop up that there are extra DNL errors.There may be a few cases were other parts fail, that could also lead to ADC drift, but this would be rare. There are cases (not drift) of ADC failure that are repairable (though not easy) - especially failing comparators.

author: maat
author_rank: Regular Contributor
timestamp: February 23, 2021, 09:24:30 am
content: Quote from: martinr33 on February 23, 2021, 04:23:47 amWell it doesn't really take any real patience. Just a Raspberry Pi and a GPIB adapter. Then let the 3458A run for a few days, executing ACAL DCV in a loop and log the CAL? 71, CAL? 71, and CAL? 175 value. The last command queries the temperature at which ACAL DCV was done. It has a higher resolution than the TEMP? command.Then finally run a linear regression against both time and temperature and you will see where it goes. The SN18 test is a poor man's version of this and if you see a clear linear drift, the numbers given in SN18 are clearly bollocks in this case because their fundamental origin are different (their reasoning and derivation was given by Dr. Frank somewhere in this forum). A faulty U180 also has a higher tempco.Attached is a sample of a faulty U180. If you want the Python script let me know. I guess this topic is drifting away from the original issueEdit: Added the Python script

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 23, 2021, 11:40:50 am
content: Quote from: maat on February 23, 2021, 09:24:30 amVery nice graphs and I really appreciate that you don't give the slope of the fit with an absolute silly amount of digits, but giving some valuable number together with std. dev.

author: maat
author_rank: Regular Contributor
timestamp: February 23, 2021, 02:23:01 pm
content: I was asked to elaborate a little on my plot. I have attached the Python script to the first post and here is what I do:I do assume there is a linear dependency on the temperatureandtime. Writing the whole thing in R would probably make more sene, but Python has a nice API to use R-style formulas:Code:from statsmodels.formula.api import olsmodel = ols("value ~ numeric_date + temp_deviation", data).fit()print(model.summary())Herevalueis the value of the CAL?72 variable,numeric_dateis the number of days since the start of the measurement,temp_deviationis the deviation from the mean temperature. Now, the model is a multiple linear regression, because thevalueshould depend on both temperature and time. This is important, one cannot do a simple linear regression and either extract the tempco or drift, they have to be extracted at once. The formula simply states, that the columnvalue(left) is related to both the columnsnumeric_dateandtemp_deviation(right), and then we want to run ordinary least squares (ols) on it. The next line then prints the summary of the fit.The script I have attached, can typically easily be extended to work with any data source. Those data sources can be found in the file_parser.py file. Feel free to add your own.Toggle the booleanplot_tempcoto show either the drift plot or the tempco plot.Edit: A bit of trivia: The A3 board died 3 months later @24/7 usage with a convergence error. So this plot can be considered end of life.

author: martinr33
author_rank: Frequent Contributor
timestamp: September 11, 2021, 11:29:35 pm
content: Some pictures of early U180 devices.Both have handwritten numbersThe earlier unit has the part information on a sticker on the underside, which explains why some of these are blank.I used Chipquik to remove one, and am still cleaning up the mess.The second one, I removed the solde with a solder sucker. This approach did not free the pins. I took it the rest of the way with a hot air pencil, and the package fell out.I am going to see if baking gets me anywhere.

author: Extrasolar
author_rank: Contributor
timestamp: September 23, 2021, 02:13:09 pm
content: Hello,Here are a couple of images from my dead U180 (Resistor Network Ceramic):

author: Extrasolar
author_rank: Contributor
timestamp: September 23, 2021, 02:26:12 pm
content: Also some images from the Current Steering Section (JFET Switches):

author: YetAnotherTechie
author_rank: Regular Contributor
timestamp: September 23, 2021, 05:16:00 pm
content: The top edges of the pads look corroded? the line between the pad and the resistor tracks.

author: chekhov
author_rank: Regular Contributor
timestamp: September 23, 2021, 05:27:56 pm
content: Extrasolar, how you got rid of black resin/coating ?

author: Extrasolar
author_rank: Contributor
timestamp: September 23, 2021, 05:36:46 pm
content: Quote from: chekhov on September 23, 2021, 05:27:56 pmHi Chekhov,I used Fuming Nitric Acid, that did the job allright (only for the resistor networ) !! The Current Steering Section, needs just a tiny drop of acetone, it disolves rapidly the coating.I am currently working on a RE attempt on the U180and the video will hopefully be uploaded sometime in November this year on my channel on Youtube.Kind Regards

author: Extrasolar
author_rank: Contributor
timestamp: September 23, 2021, 06:27:55 pm
content: Quote from: YetAnotherTechie on September 23, 2021, 05:16:00 pmHi,I think thats just residue from the coating !!

author: MiDi
author_rank: Frequent Contributor
timestamp: September 23, 2021, 07:34:10 pm
content: Quote from: Extrasolar on September 23, 2021, 05:36:46 pmLink pls

author: Extrasolar
author_rank: Contributor
timestamp: September 23, 2021, 10:15:12 pm
content: Quote from: MiDi on September 23, 2021, 07:34:10 pmhttps://www.youtube.com/user/pitushi/community

author: TiN
author_rank: Super Contributor
timestamp: September 23, 2021, 10:40:46 pm
content: Looking forward on your exposure for U180. If you need a hosting for hi-res RAW files or whatever, just ask.

author: Extrasolar
author_rank: Contributor
timestamp: October 05, 2021, 12:58:57 am
content: I found an interesting State Machine on top of the U180, with maybe more than 2 metal layers ... So far it has been very difficult to RE, but will get there nonetheless !!

author: Extrasolar
author_rank: Contributor
timestamp: October 12, 2021, 12:40:10 am
content: Hi All,There are some nice updates from the U180 RE attempt.After learning how to spot the various transistors, the overall process becomes very simple. Nonetheless, there are some areas that are way out of focus so I will have to scan em again.So far, everything has been scanned and extracted, only the decoder remains (I wrongly assumed that the section was a sequential circuit thus a state machine, but it is just combinatorial). The decoder is easy so no hustle there.There is another section which handles the FET Channel Modulation. I am going to use MOSFETS instead of JFETS so will think of an analog loop to "modulate" the MOSFET Switches.There are 18 Drivers for the Switches, most probably those are Latches so not a problemThe Resistor network can be reproduced with 0.1% value tolerance and 0.1% matching tolerance (about 200 Euros/piece in a ceramic substrate inside a larger ceramic package with golden pins).Will produce a couple of prototype PCBs with different features just to test out more possibilities...

author: Kleinstein
author_rank: Super Contributor
timestamp: October 12, 2021, 10:44:15 am
content: Are the main reference switches JFETs or MOSFETs (lateral or vertical) ? From what I have read this is not so clear.For a replacement, the choice of switch fets could be a bit tricky: the 3458 uses 50 K for the input path and 40 K for the main reference paths. To get good compensation of the switch TC one would need switching FETs with a resistance ratio of 5 to 4.AFAIK there is some "substrate" modulation depening on the input voltage. This makes some sense to reduce the quare part in the switch resistance. When changing the FETs, this needs to be addressed too. With MOSFETs an alternative is changing the drive voltage for the input path.The resistor value matching should not be so critical. A tricky part can however be TC matching and coupling for the input and main reference path. Self heating can result in V³ type nonlinearity as one principle part to the INL.

author: Extrasolar
author_rank: Contributor
timestamp: October 12, 2021, 01:19:37 pm
content: Hi Kleinstein,The main Switches are JFET !!Since I'm going to use MOSFTES(charge inj. 3pC, leakage 10pA, fc at around 200MHz), I was thinking of placing a modulation scheme ahead of the switch to compensate(not sure if to proceed with this approach or use another). I am also considering extensive simulation for the JFET channel modulation, taken all the dimensions of the switches and mapped all on Cadence.I believe it can be done easily but since I have not prototyped that, I cant tell for sure !!

author: Kleinstein
author_rank: Super Contributor
timestamp: October 12, 2021, 01:38:22 pm
content: For most of the FETs one should not need anything special, just the normal gate control, maybe something to reduc the gate charge spike.There should be only FETs with special needs: the ones for the input signal(s) 40K and 10K for the high speed mode. These may want something like individual voltage for the gate drive, like 1/5000 of the input voltage added to the gate voltage.The leakage specs of the FETs would be only a minor part. The interresting parameters are capacitance and on_resistance. I would consider something like an ON resistance of about 1/5000 to 1/2000 the series resistor for the FET a suiteable order of magnitude. So some 10-25 Ohms for the 50 K reference resistors.Anyway, with a recreated / coppied U180 chip one can not directly expect the same performance as the original 3458. There is a chance to get similar performance, but still would need the full testing much like a new design.

author: iMo
author_rank: Super Contributor
timestamp: October 12, 2021, 01:57:41 pm
content: Do we know where the U180 in the new black edition come from?

author: Extrasolar
author_rank: Contributor
timestamp: October 13, 2021, 09:38:58 pm
content: Hi Guys,Some very nice updates on my U180 RE project are now on Master Ken Shirriffs Twitter account:https://twitter.com/kenshirriff!!Kind Regards

author: Extrasolar
author_rank: Contributor
timestamp: October 16, 2021, 01:45:15 am
content: Hi All,Here is a partial Decoder, with a few gates identified. It seems that it is all composed by NOR and NOT gates:

author: Extrasolar
author_rank: Contributor
timestamp: October 20, 2021, 12:28:05 am
content: Hi All,I was able to complete the Decoder section of U180, although errors might be present so, take it with a pinch of salt:

author: wutieru
author_rank: Contributor
timestamp: October 25, 2021, 12:27:12 am
content: Nice done.

author: TheSteve
author_rank: Unknown
timestamp: October 28, 2021, 03:12:37 pm
content: https://www.keysight.com/my/partDetail/03458-6653342 in stock!

author: niner_007
author_rank: Frequent Contributor
timestamp: October 29, 2021, 02:01:36 am
content: Quote from: TheSteve on October 28, 2021, 03:12:37 pmRoyal cool, I have a stash of 5 from when they were selling them, let me see if I can extend my stashIt's very cool seeing Keysight committed to reparability like this. <3

author: wolfy007
author_rank: Frequent Contributor
timestamp: October 29, 2021, 06:58:59 am
content: Quote from: niner_007 on October 29, 2021, 02:01:36 amYou need more than 5 spares? How many 3458A's do you have?

author: TheSteve
author_rank: Unknown
timestamp: October 29, 2021, 03:57:21 pm
content: Quote from: niner_007 on October 29, 2021, 02:01:36 amDo you test each board before tucking them away? One of my original "refurbed" A3's had excessive noise and I had to return it.I'm flying fast and loose now, no spares on hand.and down to 40 in stock now.

author: eplpwr
author_rank: Regular Contributor
timestamp: October 29, 2021, 06:41:39 pm
content: Quote from: TheSteve on October 28, 2021, 03:12:37 pmI think KS have different stock locations; yesterday the number of stocked was 23, now it is 17. So, probably different warehouses and different # in stock. I'm in Europe, as my country flag signifies.

author: niner_007
author_rank: Frequent Contributor
timestamp: November 01, 2021, 10:00:33 pm
content: Quote from: wolfy007 on October 29, 2021, 06:58:59 amToo many, you don't want to know

author: tonyz663
author_rank: Newbie
timestamp: November 18, 2021, 02:17:21 am
content: I am a newbee on this forum and I just purchased one of the new A3 boards (66533) from Keysight and installed it on my older HP 3458A. My old A3 board was not working properly. I am now getting a "202 Hardware Error - Slave Test: Convergence" when I turn on the meter and each time I try to reset it. When I Autocal it, it gives me a "209 Unable to Read A/D" error and a "101 Calibration Error" after going through the routine. I was curious if anyone else was experiencing this issue as well with the new A/D boards and if there is something I am missing? FYI - I have replaced all of the A5 NVRAMs a short time ago. Is there a software update I need to do? Just not sure at the moment. Let me know your thoughts!

author: wutieru
author_rank: Contributor
timestamp: November 18, 2021, 02:29:40 am
content: I also bought 66533 but haven’t received it yet. After I test it and tell you the result.

author: TiN
author_rank: Super Contributor
timestamp: November 18, 2021, 03:10:34 am
content: Tonyz663 , sounds like you might have problem with A6 or A5 boards (or less likely but possible A1 and\or power supply), if you see those faults with replacement A3. Do you get any readings from meter? How about self-test?

author: tonyz663
author_rank: Newbie
timestamp: November 19, 2021, 12:50:40 am
content: Thanks for the reply TIN. I've enjoyed your in-depth repair discussions for the 3458A! I'm beginning to think there is an issue with the new A3 board. I just re-inserted my drifty original A3 board and it passed the self test and no errors. And it is actually reading voltage now. So, I don't think I have issues with the other boards at the moment. Do you have any experiences with this latest A3 board? There could be something I am missing?

author: TiN
author_rank: Super Contributor
timestamp: November 19, 2021, 03:34:46 am
content: Interesting. If no errors with your old A3, I'd reach out to KS and asked them for replacement of your replacement A3 board. It's not first time that those refub boards were actually not working and needed additional refub once more.

author: branadic
author_rank: Super Contributor
timestamp: November 19, 2021, 05:44:51 am
content: QuoteI have the impression that 03458-66523 designed by Wekomm GmbH is backwards compatible, while 03458-66533 redesigned from 03458-66523 by KS for some odd reason isn't. The boards offered are not refurbed but new.https://www.keysight.com/my/partDetail/03458-66523https://www.keysight.com/my/partDetail/03458-66533Edit: Which firmware version are you running, the latest 9.1?-branadic-

author: TiN
author_rank: Super Contributor
timestamp: November 19, 2021, 06:53:35 am
content: Perhaps tonyz663 can take some hi-res photos of his board and shine some light for us here. That would be nice."Wekomm" board works fine in old 3458A, even with older Rev4 firmware.

author: tonyz663
author_rank: Newbie
timestamp: November 19, 2021, 06:06:42 pm
content: Well, after a phone call with Keysight and a follow-up e-mail, they tell me that I need a firmware update to 9,2 on the A5 board. The new 66533 boards will not work with 7,2 or 8,2 version (I currently have 8,2). My A5 board has one ROM on it. Is there a way to update my current A5 board to 9,2? I don't have a UV eraser on hand. I can program chips with my BP programmer however. Is there a different chip I could put in and program instead of using the original UV chip? Is there a 9,2 file available to program the ROM with? Let me know!In checking with the Parts ID team, it sounds like you need to update the firmware. Please let me know if you have any questions or if I should close the case."Customer can refer to Service Note 12C. 3458A, serial number 2823A15426 is an older instrument. This one left the factory pre-2001. Firmware upgrade (ROM replacement) is the only solution for an older 3458A. 3458A OLDER Models SN Prefix 2823 are not compatible with the new 03458-66523/333458A A3 A/D Converter incompatibility issueP/N 03458-66533 REV 4 A/D converter board for the 3458As but I get a error stating "ERRSTR 202, "HARDWARE FAILURE – SLAVE TEST: CONVERGENCE".Regarding the problem description, the assemblies are not DFS/DOA. The issue from what we know at this time is older 3458A firmware revisions (7,2 – 8,2) are not compatible with the new 03458-66523/33 assembly. The latest revision 9,2 – shipping for several years, is compatible. The serial number specified, particularly the ‘2823’ prefix, indicates this an older unit likely manufactured in Loveland when we were HP. My guess is the customer’s unit has revision 7,2 or 8,2 installed.One solution now is to upgrade the firmware which requires a new A5 assembly. Kit 03458-80049 is available and in addition to containing the latest firmware, it also enables extended memory within the 3458A."

author: branadic
author_rank: Super Contributor
timestamp: November 19, 2021, 06:28:04 pm
content: Please check:https://xdevs.com/fix/hp3458a/#firmware-branadic-

author: MiDi
author_rank: Frequent Contributor
timestamp: November 19, 2021, 11:55:39 pm
content: Eprom eraser or UV-C lamps are quite cheap.Hi-res photos of new A3 appreciated.

author: maat
author_rank: Regular Contributor
timestamp: November 20, 2021, 10:46:29 am
content: The EPROM usedshouldbe an ST M27C4002. You can get those new from the Bay for a few dollars. Do check though, there are different versions of the A5 board around. Some have multiple EPROM chips. The new ones will be empty and you programm them once (unless you get an eraser). Sometimes, if the chips are really old, you might not be able to fully erase them and have to get a replacement anyway.

author: tonyz663
author_rank: Newbie
timestamp: November 20, 2021, 03:06:06 pm
content: Here are some photos. Fighting a bit with the photo file sizes!

author: tonyz663
author_rank: Newbie
timestamp: November 20, 2021, 03:07:11 pm
content: Another photo:

author: tonyz663
author_rank: Newbie
timestamp: November 20, 2021, 03:10:59 pm
content: More photos:

author: tonyz663
author_rank: Newbie
timestamp: November 20, 2021, 03:11:40 pm
content: Last photo:

author: michael_liu4444
author_rank: Contributor
timestamp: November 22, 2021, 07:51:51 am
content: Dear Sir,I am looking for a good A/D Board A3 (03458-66503 or 03458-66513).Do you know know any one who want to sell to me ?Requirement: after install the board into a 3458A, the 3458A should be able to pass self-test and AutoCal.Please send a message to my email: michael_liu4444@163.comThanks & regards,Liu Biao

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: December 01, 2021, 08:21:42 pm
content: Hello Voltnuts,does anynone know why KS suddenly changed its policy and started to sell again these boards at acceptable cost ?I have ordered a spare board - placed the order - and a few hours later I observed price went up from1004€to 1068€.Or is KS only selling these 03458-66533 until stock lasts as next step up version will have the backwards sw compatibility bug removed ... (speculation) ?Herzliche Grüße/Meilleures salutations/Best regardsScoobyDoostill4211120to go :https://www.keysight.com/my/partDetail/03458-66533

author: aronake
author_rank: Frequent Contributor
timestamp: May 22, 2023, 04:21:40 pm
content: what is the latest on keysight spare part sales? are boards available? Seem they stopped selling, then starts again and now i see indications that they do not sell, but only do repairs.

author: KT88
author_rank: Frequent Contributor
timestamp: May 22, 2023, 08:27:16 pm
content: currently you have to send it to them to get a quote. i‘ll possibly do it with my 3458a soon. my guesstimate would be between 2k…4k.

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: May 29, 2023, 05:10:13 pm
content: Hello folks,In December 2020 following price levels were listed on website of KS:https://www.keysight.com/my/partDetail/03458-40212113€https://www.keysight.com/my/partDetail/03458-402147,50€https://www.keysight.com/my/partDetail/03458-437017,50€https://www.keysight.com/my/partDetail/03458-437027,50€https://www.keysight.com/my/partDetail/03458-441135,82€https://www.keysight.com/my/partDetail/03458-4791181,45€https://www.keysight.com/my/partDetail/03458-62111255€https://www.keysight.com/my/partDetail/03458-4933129,08€https://www.keysight.com/my/partDetail/03458-66527390€https://www.keysight.com/my/partDetail/03458-6791265,44€https://www.keysight.com/my/partDetail/03458-66675975€So one can use these to understand how much prices have increased at Keysight for whatever reasonsBest regardsScoobyDoo

author: aronake
author_rank: Frequent Contributor
timestamp: June 11, 2023, 04:06:30 pm
content: Quote from: ScoobyDoo on May 29, 2023, 05:10:13 pmThese links all still works, and there are updated prices. Do anybody know if these more "basic" spare parts are possible to buy from Keysight or they stopped selling everything?I am looking for a front panel (03458-40212) if anyone have one to sell.

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: June 15, 2023, 06:15:29 am
content: Hello aronake - You will need to contact local Keysight service center - the white version has limited stockand KS might ask You more details about your instrument before granting permission.[otherwise some dealer / stockist would buy all remaining stock and just ask what they want].The situation (local policy) might be different from continent to continent - in Europe You must be a registeredKS customer before they accept & process the order.An option could be to ask AB Precision in Germany if they can ship You such white front panel - but it might come with extra export charges (EU -> HKK) and some extra margin on top. (https://www.ab-precision.de/)Don't forget to order the red bezel (03458-49331) if Yours need replacement.I agree - since there is a new wind inside Keysight - cost of spare parts has almost doubled and it becomes hard to deal with them.I would recommend not to wait too long as these are available until gone (in white colour).Best regardsScoobyDoo

author: aronake
author_rank: Frequent Contributor
timestamp: September 06, 2023, 04:13:02 pm
content: Here is a find that may help someone.New A3 are not orderable, but the keysight spare part website list this refurbished A3 as orderable. 1996 USD thought.... but still less then sending in the meter and have Keysight replace it.https://www.keysight.com/hk/en/ecom/parts/part-detail.html/03458-69503

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: September 09, 2023, 05:55:43 am
content: KS already removed the pricing 1935€ | 1996USD ... - these were refurbished boards.I don't expect to see KS offering new tested boards in near futureQuote from: aronake on September 06, 2023, 04:13:02 pm

author: aronake
author_rank: Frequent Contributor
timestamp: September 14, 2023, 09:22:46 am
content: There are LOTS of reports who bought a 3458a with U180 drift, but sas anyone owned a 3458a that has started to develop severe U180 drift while owning it?There should be millions of hours of 3458a usage among eevblog users, and if that is not the case, it kind of points toward these u180 faults came from the factory.

author: MiDi
author_rank: Frequent Contributor
timestamp: September 14, 2023, 01:38:06 pm
content: Quote from: aronake on September 14, 2023, 09:22:46 amDefinitely, hard to judge if an instrument that fails after dozens of years can be called faulty from factory...There were batches that had issues with U180 from factory and Agilent repaired them.

author: dietert1
author_rank: Super Contributor
timestamp: September 14, 2023, 03:36:33 pm
content: I think failure in a 30 or 40 year old instrument is normal. The problem is how to get it fixed.Some days ago i fixed a Technics SU-VX920 stereo amplifier. It's of similar age and a pretty big one. The problem was the mains switch: Its contacts had pretty much vanished and turned into dust. Of course the part isn't available anymore, yet much easier to replace by something similar than the hybrids in old HP multimeters.Regards, Dieter

author: aronake
author_rank: Frequent Contributor
timestamp: September 15, 2023, 04:27:37 am
content: Quote from: MiDi on September 14, 2023, 01:38:06 pmIt is absolutely true that an instrument that fails after dozens of years can be called faulty from factory.But question was is anybody here who owns a 3458a have seen it develop this fault over their ownership. Lots of reports of people who bought a faulty, but I think I have not seen anyone reporting in that drift developed over time while owning one. And if no fault has developed over the millions of 3458a hours among EEVforum user time that kind of indicate that use is not much of a trigger of a fault event but that the meter may have had drift from the factory.What of course may also be the case is that pretty much all meters people have here are used. And if the meter do not develop drift after the first years, then it is very likely to never develop any drift. And people here either get one used that is safe as drift never developed, or get and used where drift has developed.The second theory sound more plausible.

author: dietert1
author_rank: Super Contributor
timestamp: September 15, 2023, 06:39:50 am
content: The reason for not reporting about newly developped and unfixable drift should be the same commercial reason that makes people dump drifty instruments at ebay without mentioning the problem. The drifty ones won't vanish except by repair or by hiding the problem.Regards, Dieter

author: aronake
author_rank: Frequent Contributor
timestamp: September 15, 2023, 07:03:12 am
content: Quote from: dietert1 on September 15, 2023, 06:39:50 amThat an interesting thought. But people happily tell about 3458a they bought that were drifty, and that would put them in same position as telling about a 3458a that developed drift while owning it.There are indications that the 3458a Agilent sold and had the recall/repair notice for was drifty at delivery but not noticed in the pre-shipment testing. Kind of makes sense, each meter would need to be tested for weeks to be certain. So maybe then lots more of 3458a was sold bad. Or maybe pretty much all that now are discovered to have drift had it from the factory. And that the drift is nothing that comes from use, but from the factory.

author: srb1954
author_rank: Super Contributor
timestamp: September 15, 2023, 07:23:24 am
content: Quote from: aronake on September 15, 2023, 07:03:12 amIt would be interesting to do a poll amongst owners, particularly with those who owned from new, to determine the prevalence of drift-prone units and when the drift problems were discovered.QuoteIt would also be interesting to discover when HPAK realised that there was a problem and started to do something about it. My unit is a 2005 build and it had severe drift problems when I acquired it approx 2 years ago. So it appears HPAK, even at 15 years after the product's initial introduction, either hadn't realised that there was a problem with the product or were not prepared to remedy the product issues.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 15, 2023, 09:04:34 am
content: For the date they were aware of the drift problem, this is relatively easy as there is the service note to describe the drift test. For sure they realized the problem / weak point.The problem for HP/KS may be that they likely produced quite a lot of the U180 chips up front and they may not have a good way to really fix the problem.With old drifty units sold on ebay and the good units kept at the cal labs and similar commercial users the picture on the failure rate may look higher than it actually is. We don't hear much about old units still running with no problems (except maybe the SRAM/battery change).

author: aronake
author_rank: Frequent Contributor
timestamp: September 15, 2023, 05:13:22 pm
content: Quote from: Kleinstein on September 15, 2023, 09:04:34 amThat's a good point and adds maybe the most plausible explanation: The drift problem is very rare and may also very rarely develop over time (explaining why very few people have reported that their 3458a suddenly start to drift). Meaning that there are lost of 3458a out here having no issues and it is very rare that a 3458a develop drift over ownership, but those that develop drift are very very much overrepresented in the used market (explaning why many people happen to get 3458a that are drifty).

author: srb1954
author_rank: Super Contributor
timestamp: September 15, 2023, 08:16:02 pm
content: Quote from: Kleinstein on September 15, 2023, 09:04:34 amThe service note 18A, which was issued 13 February 2007, states "Some recently produced 3458As ..." and only covers a relatively small range of serial numbers that might have drift problems. I looked up the serial number of my unit, which is after serial number range stated in the service note, on the service support websitehttps://support.keysight.com/s/product-serial-details?language=en_USand this does not recommend that my unit be checked against the service note 18A procedure. This is despite it having severe drift and having to have a replacement board fitted by Keysight to fix the problem.It appears to me that HPAK have not fully acknowledged the problem as there are plenty of users reporting drift problems dating back to the earliest production units but HPAK appear to be silent in relation to these.It would be interesting if other owners were to check the status of their units on the Keysight service support website and report whether the service note 18A procedure is recommended for their units and whether they have encountered drift problems.QuoteSince early units and those produced at least up to 2005 exhibit the problem it seems highly unlikely that HPAK would have ordered enough U180 chips to cover 15 years of production when the product was first introduced.

author: aronake
author_rank: Frequent Contributor
timestamp: September 17, 2023, 05:46:55 am
content: Here are my statistics on my 5 3458aProduction year A3 swap time Calnum Comments2006 2011 92 Extremely stable, opt 0021991 1999 1243 Extremely stable, used to serve in a cal lab1999 Not swapped 19 Extremely stable, used to serve in a cal lab, very good TC1998 Not swapped 1 Just passes SN18 test, but at 0.4 ppm/day not good enough. Also a bit high TC.2000 Not swapped 8 Suffers very high TC, around 1 ppm/C, so drift kind of masked by TC, but fair to assume its drifty.The 1998 and 2000 meters have statistical bias, being drifty at purchase (which I was aware of).Obviously not very strong statistics with 3 samples, but that means 67% of the stable meters have had the A3 replaced. And the drifty A3 span from 1991 to 2006 here. And seems there are much newer meters that developed (or had from production) drifty A3.1998 meter looked terrible when i got it. It has serial 2823A20500, so closest brother to one of Tins repair projectshttps://xdevs.com/fix/hp3458_u4/. So maybe the "angry hulk" bought two meters to abuse in parallel.... It looks nice now after some refurbishment, but has some A3 drift. Over half a year it has come down from 0.6 ppm/day to just under 0.4 ppm/day. so maybe if it is allowed to run for another year or so it may get acceptable.

author: srb1954
author_rank: Super Contributor
timestamp: September 17, 2023, 08:16:07 am
content: Quote from: aronake on September 17, 2023, 05:46:55 amI can only add one data point to your statistics:Production year A3 swap time Calnum Comments2005 2022 56 Had severe drift prior to replacement of A3 at 1.6ppm/day per the SN18 test. After replacement of A3 drift dropped to 0.003ppm/day but temperature coefficient is a little on the high side at 0.43ppm/℃Did you check the serial numbers of each of your units on the Keysight service support site for recommended updates? There are probably a number of updates/fixes that apply to your earlier units.

author: aronake
author_rank: Frequent Contributor
timestamp: September 19, 2023, 02:57:12 pm
content: I felt like being a bit experimental. So had the U180 swapped between the A3 that have a bit of excess TC with the one that have a bit of, but still in spec drift. The U180 is pretty easy to desolder if using a good desolder gun. Just had everything packed together and started some new test runs." alt="" class="bbc_img" />

author: MiDi
author_rank: Frequent Contributor
timestamp: September 12, 2025, 06:52:53 pm
content: Bit off topic, but seems best fit and not worth to start a new topic.3458A A3 Schematic incl. BOM - KiCadAll errors in schematics from CLIP should be fixed and additional annotations of minor changes in later revisions (no major changes e.g. patchboards or SMD version).If there are errors or questions reach out to me via PM or justopen an issue on GitHubto not spam this topic.