3458A CAL & repair - Page 1
Forum section: electronics / general

author: IanJ
author_rank: Unknown
timestamp: March 15, 2018, 11:53:28 am
content: Hi all,So I put my 3458A to Keysight here in the UK for CAL and they've come back (email) today saying it has a "faulty front/rear terminal switch which is causing issues taking measurements and will require repair".Am awaiting the repair engineer to contact me which I presume is to ask if I want to go ahead with the repair etc.....but I've no idea if they mean the actual switch mechanism or if it's any related relays (if there are) etc.Any thoughts?Ian.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 15, 2018, 12:58:00 pm
content: You have bought your 3458A 'used', and it's more than 10 years old, isn't it?And it fails 2W Ohm zero @ 10 Ohm and 100Ohm range?It's very probably the same error as on the well known one of the 34401A:https://www.eevblog.com/forum/testgear/hpagilentkeysight-34401a-2w-problem/The switch is very similar, at least same supplier.My 3458A (vintage 2000) also showed signs of rising contact resistance, which I could mitigate by frequent actuation of front / rear switch.Maybe they can calibrate front or rear only.You may then clean it on your own, and check zero on your own.As in the 3458A, the switch assembly is relatively small, it may not cost so much to replace it @ KS.regards Frank

author: IanJ
author_rank: Unknown
timestamp: March 15, 2018, 05:40:45 pm
content: Out of interest, is there any way to tell age of the unit from the serial no.....?Mine is an HP branded unit (with a new KS front panel).Ian.UPDATE: Mine is a 2823A prefix so from what I read means 1988 through to mid 90's.Ian.

author: kj7e
author_rank: Frequent Contributor
timestamp: March 15, 2018, 06:28:49 pm
content: Not exact age, but it was built sometime not log after 1988. The prefix only shows the model year series until the next revision was made.I had a 3478 with a flaky front/rear switch. Everything was fine until one day I pressed the switch then the Ohms readings where no longer stable. I suspect it had been many, many years since it had been pressed. A little contact cleaner and lots of cycling helped resolve the issue. I looked in to replacing it, but it was no longer available. If you can get a new switch for not much $, I would consider it.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 15, 2018, 06:32:21 pm
content: Quote from: IanJ on March 15, 2018, 05:40:45 pmNope, that doesn't work for the 3458A. From the Prefix, you can't tell the Vintage directly. Mine from 2000 has the very same one.The serial number itself will tell, Joe Geller once had a list on his site, but that link vanished - pity:http://www.gellerlabs.com/HP%203458A%20DMM.htmAs you have a HP branded instrument, it's definitely before 2001, as that's about the year when agilent took over.Ser No's 2823A25xxx are about from 2000.If you registered your instrument on 'myKeysight', you may also find the origin of your instrument and the vintage on the KS Infoline, like so:https://service.keysight.com/infoline/public/details.aspx?pn=3458A&sn=2823A25500&i=DOC&from=details&BTN_QUERY_MODEL_SERIAL=NextPlease check with KS the exact error.If it's what I suspect, you may save a lot of money. If it's something different, as a failure in another mode, it may be a relay, as you supposed, which means that KS will replace the analogue board for a fortune.Frank

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: March 15, 2018, 07:53:56 pm
content: Another clue on 3458a age (it's not serial number I know) - just open it up and look for youngest component date codes. It won't be exact, but at least you'll have a general idea of what era you've got, or at least when an assembly was replaced.If the unit was always cal'd at HP / Agilent / KS they will have records - that doesn't always work but worth a shot asking. When we send our units in the paperwork comes back with a complete repair / cal history. They should at least be able to look up sales date based on serial number. We've had luck with that before.Not sure how it works in the UK - but in the US you never send in your 3458a without first buying the extended warranty...if the unit is in current cal they will sell you the warranty, usually less than $200/yr. Then the repairs are -much- more reasonable, and you get a discounted price on the cal too. Worth every penny if you depend on your equipment that might need a repair now and then - and whenever time = money.

author: Andreas
author_rank: Super Contributor
timestamp: March 15, 2018, 08:08:26 pm
content: Quote from: Dr. Frank on March 15, 2018, 06:32:21 pmI downloaded this article from Joe. (you never know when you need it).with best regardsAndreas

author: martinr33
author_rank: Frequent Contributor
timestamp: March 15, 2018, 10:04:54 pm
content: Andreas - do you have the Geller serial number file? It isn't in the archive you posted.And the switch assembly is available from Keysight but...A10 Front/Rear Switch for the 3458A Orderable US$ 684.00I've looked for the switch alone from distributors, but can never find the gold version. TiN reports getting one from HP P/N 3101-2969 for $75, but that is not in the current parts list - I suspect he got it through some other route. Either way, you will probably want to get the meter back so you can fix it, assuming you don't want to pay the $684 + labor. If you have a drifty ADC (good bet that you do) and a weak display, you are close to the HP Big Fix price.One failure cause (not in your case, but to be watched for) for the switch is, if the front retainer pops off the switch actuator, you have to find the flying spring and watch out for a little piece of bent wire that is the front/rear latch pin.I had a Keithley meter with a flaky F/R switch. I used Deoxit - which fully restored operation.I flushed the Deoxit, and it went flaky again.So I left a little Deoxit in there, and all is good.

author: Andreas
author_rank: Super Contributor
timestamp: March 15, 2018, 10:43:29 pm
content: Huh,I have only the HTML-text. no extra file.with best regardsAndreas

author: IanJ
author_rank: Unknown
timestamp: March 19, 2018, 12:46:46 pm
content: Update:-Keysight got back to me today.They won't replace the switch, it has to be the whole A10 board.EUR 52.93 (SHADOW SWITCH P/N=3101-2969)versusEUR 618.00 (A10 FRONT/REAR SWITCH ASSEMBLY P/N=03458-66510)I suggested they could remove A10, send to me, I'd replace switch and send back but they are not biting.......saying that the 3458A has to come back to me, then when it's resent I pay for full cal again.So, I've told them I am only interested in DCV right now (I manufacture voltage references)........so conditional calibration for the rest will do.......then I'll get a new switch in time for next year recal. Hopefully they will be ok with that.QUOTE FROM KEYSIGHT:-It seems to be behaving itself at the moment, ie. It passes the front and rear 0 Ohms Self-cals, but during calibration they couldn’t get the correct readings.(approx. 2.4 Ohms on the front and 1.6 Ohms on the rear).We can return the unit to you as a Conditional Calibration (there are also some “Undetermined” results on some of the AC measurements) and youwill be charged the cost of an Accredited Cal.Ian.

author: IanJ
author_rank: Unknown
timestamp: March 21, 2018, 07:57:02 am
content: Update: I asked Keysight when my 3458A was made.......they've come back with Feb. 2000. Good to know!Ian

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 21, 2018, 09:01:06 am
content: Quote from: IanJ on March 21, 2018, 07:57:02 amSo all my guesses came true, including vintage / ser. no. of your instrument.And you may repair the switch by yourself, afterwards repeating the zero calibration, which does not spoil the 10kOhm / 10V basic calibration.Frank

author: TiN
author_rank: Super Contributor
timestamp: March 21, 2018, 10:21:03 am
content: If calibration was done with faulty zero, resistance calibration will be spoiled after repair as well.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 21, 2018, 11:19:36 am
content: Quote from: TiN on March 21, 2018, 10:21:03 amI doubt that, because 40kOhm value is determined in 4W mode, where zero calibration is not relevant.This particular error affects 2W Ohm only.Frank

author: IanJ
author_rank: Unknown
timestamp: March 21, 2018, 12:47:10 pm
content: Quote from: Dr. Frank on March 21, 2018, 09:01:06 amI hear you, but I'll not replace the switch until just before next recal. Don't want to upset anything.Ian.

author: ap
author_rank: Frequent Contributor
timestamp: March 22, 2018, 03:45:24 am
content: Quote from: IanJ on March 21, 2018, 12:47:10 pmThats the right approach. There are users who state they never toggle the switch because they have no rear connections, and still the item fails when sent to cal. So if you replace it now, that may not necessarily help you. I would even go further and just start toggling the switch prior to sending it to next cal, and watch how it behaves over a period of time. You can easily verify the 0 ohms. If it is unstable only, which I doubt, then I would replace it.The other thing is, if you just need DCV calibration, any good cal lab can do that, and it will be at a much better price. Keysights uncertainty is not very exciting, 2ppm as per manual, which adds to the uncertainties in the data sheet. They may be lower when they do their gold cal or whatever, probably also depends on where its done.

author: Tony_G
author_rank: Super Contributor
timestamp: March 22, 2018, 04:02:50 am
content: Quote from: ap on March 22, 2018, 03:45:24 amI think that is because the cal process does both front and rear connectors - If you could just get a "Front cal only" then it'd probably work for those customers.Mine failed the same part of the test but it turned out to just be the crimping so recrimping fixed that.TonyG

author: IanJ
author_rank: Unknown
timestamp: March 23, 2018, 06:20:51 pm
content: Back home........Ian.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 23, 2018, 07:58:17 pm
content: Hi Ian,the calibration documentation of your instrument are not online...I'm curious, how this conditional calibration looks like, would you mind copying the report here?Maybe you have access to the file ones KS site, so that you may link the complete doc.Thank you!Frank

author: IanJ
author_rank: Unknown
timestamp: March 23, 2018, 09:28:08 pm
content: Quote from: Dr. Frank on March 23, 2018, 07:58:17 pmAs attached........comments welcome.PS. The docs are online but the case is still recorded as open so maybe thats why you couldn't see.Ian.

author: technogeeky
author_rank: Frequent Contributor
timestamp: March 23, 2018, 09:48:49 pm
content: Quote from: IanJ on March 23, 2018, 06:20:51 pmThat's a pretty awesome bit of kit to have, and an awesome sticker to have on it. Especially as a "hobbyist." Congrats!

author: IanJ
author_rank: Unknown
timestamp: March 23, 2018, 10:44:14 pm
content: Quote from: technogeeky on March 23, 2018, 09:48:49 pmThe 3458a earns its keep........I use it to cal the PDVS2's that I produce and sell.Ian.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 24, 2018, 08:29:47 am
content: Quote from: IanJ on March 23, 2018, 09:28:08 pmIan, thanks again, it's really interesting / puzzling...Obviously, your instruments passed Ohm completely after adjustment (As Completed), also this 2W zero error of 1.6 .. 2.4Ohm has been successfully 'removed' by adjustment.As they had to actuate the front/rear switch for that check, and as the zero reading was ok afterwards, maybe the switch itself might be ok, but the crimping not.. depends a bit on when they checked the zero reading, either directly after adjustment, or afterwards, in a 2nd attempt.As I already assumed, this error does not affect at all the gain calibration of the Ohm mode, 10k and 100k are spot on to < 1ppm after adjustment.Same goes for the current ranges, which were "Undetermined" before.It's a bit strange, why they set status Undetermined in several modes/ranges during As Received, and even after adjustment.. there's no obvious failure.Frank

author: IanJ
author_rank: Unknown
timestamp: March 24, 2018, 11:45:03 am
content: Quote from: Dr. Frank on March 24, 2018, 08:29:47 amI'll have a look when I remove the board to replace the switch in a years time......Any ideas what/where to look?Ian.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 24, 2018, 02:07:18 pm
content: Yes, sure.. that's assembly 66510 (see CLIP).I'd check the resistance between the jacks (front/rear) and the corresponding soldering junctions directly at the switch. 2nd, the resistance values across the switch contacts. 3rd the resistance from the switch to the analogue PCB.Frank

author: ap
author_rank: Frequent Contributor
timestamp: March 27, 2018, 07:39:59 am
content: The zero-calibration cannot compensate the high zero-ohms value you mention, it would show a calibration out of range error (which makes sense, because you never have a two-ohm-ish reading between binding posts and card input, this indicates an error). So the activation of the switch must have changed that (as is often the case). The internal wiring thus can most likely be excluded (it was not changed, and the meter seems stable now). I would just watch it over time, and you can then make a justified decision later to exchange the switch (or do it anyway, even though thats not a long term guarantee if the new switch is not toggled from time to time).

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 27, 2018, 09:35:47 am
content: Adrian, you're right.The limits of the 10 Ohm range are: CAL? 13,3 = 1,0192 Ohm, and are the same for front and rear, and for 100 Ohm range, of course.I think, it's not possible to calibrate zero, if the switch contact resistance is constantly beyond these limits, or KS has the magic command to overdrive this.I just just checked my 3458A, the calibrated resistance is about 310mOhm, which is already quite high.The zero value, using that copper wire on the jacks, gave about 50mOhm.Then I actuated the front/rear switch, and got > 1.5 Ohm in first instance, but not stable, instead quickly falling below 200mOhm again.Only after 30 actuations, the resistance was again at about 50mOhm, stable reading even after a further actuation.. strange behavior..Ian might check the calibrated zero value, i.e. CAL? 13 and CAL? 22.If KS also simply actuated the front/rear switch several times to get the initial reading below 1 Ohm, and getting this stable also, then I don't understand why they made this conditional calibration, and set several modes to UNDETERMINED, in a random manner, obviously.Makes no sense to my opinion.Maybe Ian can also ask KS, what happened there..Frank

author: IanJ
author_rank: Unknown
timestamp: March 27, 2018, 10:55:14 am
content: Hi,Yes I'll ask KS......and I'll also point them to this thread.....and I'll also look at the cal zero vals when I get back to the workshop later tonight.For me, I don't care about the rear switch and wish there was a relatively easy way to by-pass it all and remove the switch, wiring and rear posts completely......and of course which would still allow KS to cal the meter in the future (wouldn't want them to say "modded meter huh?...no thanks").It's a failure mode I would just like to see the back of......and if I had a 2nd 3458A I'd be looking into this even if it meant designing a proper PCB/loom to change it out. Hmmmm thinking about that, Adrian, if you have a used A10 assembly for sale then let me know.Ian.

author: TiN
author_rank: Super Contributor
timestamp: March 27, 2018, 11:15:17 am
content: I just checked on my rusty friends. 311 mOhm and 353 mOhm for CAL? 13,1.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: March 27, 2018, 12:05:25 pm
content: It would be interesting to know how Keysight handles calibrations on meters where the pushrods have been removed to prevent the switch positions from being moved.

author: IanJ
author_rank: Unknown
timestamp: March 28, 2018, 04:46:22 pm
content: Quote from: Dr. Frank on March 27, 2018, 09:35:47 amHi,I have just this minute modified my macro (Win7 Excel) to get the CAL? vals, as follows.......PS. Haven't formatted the results yet:-CAL? 13 = 523.461471E-03 (0.523461471)CAL? 22 = 438.050474E-03 (0.438050474)Whilst at it:No. Times Calibrated = 513458A temp = 40.5 (my 3458A is on 24/7 and is in a room at 24-25degC)Error register = 0Ian.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 28, 2018, 08:02:09 pm
content: So KS could have done a proper calibration. Switch is not fresh, but may have been rejuvenated by frequent actuation.Clean your fan, please. Also frequently, because of 24/7.13°C difference is clean, 15-16°C means wool mice = dust bunny.Frank