Agilent 34401A Bubble on PCB ... can it be saved ? (SOLVED) - Page 1
Forum section: electronics / repair

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 12, 2024, 03:28:17 pm
content: Dear All ,I have bought an Agilent 34401A with the following errors on self test : 621 , 619 , 619 , 617, 615, 613 ,612after opening it up I see this following abomination.is there hope ? or I should give up ?I have another post with some issues with said meter. I will try to get some test procedure done , BUT mine mostly works on DC except continuity that is flaky at best non trustworthy at worst.I will try to test the rest of the functions somehow ( as I don't have any standards to test it against )Let em know what you think.Thank you in advance for your time

author: iMo
author_rank: Super Contributor
timestamp: September 12, 2024, 03:42:20 pm
content: It looks like the U110 (MC34081BD) has been smoked (plus minus something around it, double check). The pcb around it has been delaminated, but unless some vias are broken, the pcb may work fine..

author: tszaboo
author_rank: Super Contributor
timestamp: September 12, 2024, 03:43:22 pm
content: Water damage. With enough determination you can fix it.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 12, 2024, 03:49:33 pm
content: It looks like the OP-amp U110 get a bit hot. That is part of the amps part, as an auxiliary buffer. If that is the only thing really broken it would be relatively easy to replace, as it is not so critical a part.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 12, 2024, 04:10:16 pm
content: Dear All ,So I checked almost any VIA I can see on the problematic part of the board. All seems good ( suspiciously someone was in here before and all the vias are filled with solder.... ) anyway.After Tinkering a bit more with the meter.-I have V DC-Continuity partial sometimes it works sometimes it does not - Diode mode is also dead same issue as Continuity- DC A ( i managed to check up to 24mA and it works)- Resistance is dead ( any resistor shows 0 ohms ) and at the beginning in the Mohms random.Is there a guideline how to continue ?Before I start replacing things since the PCB is not at its best I would like to test all theories before loading the parts canon.Thanks

author: Kleinstein
author_rank: Super Contributor
timestamp: September 12, 2024, 04:26:22 pm
content: A first thing is to check if the U110 gets too hot and thus the dark discoloration (could have been a one off latch up that the chip survived after turned off).Another points to check are the supplies, especiall the +-18 V part.For the ohms part one could check the test current - if reading zero ohms, this could be from no current.There are a few repaorts about broken ohms current sources, like a bad JFET and OP-amps. The BJT cascode is also a bit suscpect.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 12, 2024, 04:55:18 pm
content: okay U552 and Ground show -27VU551 show 18V ...this is not right ... right ?

author: chilternview
author_rank: Frequent Contributor
timestamp: September 12, 2024, 04:57:57 pm
content: Quote from: The_Spectrum.A_idiot on September 12, 2024, 04:55:18 pmSounds like U552 is shorted. Not good (easy to replace, but may have caused/be caused by other damage).

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 12, 2024, 05:03:11 pm
content: is it a good idea to inject -18V after I remove the part ? and see how it goes ?

author: chilternview
author_rank: Frequent Contributor
timestamp: September 12, 2024, 05:13:09 pm
content: You could try. Also check F101 and F102, the internal and external fuses for the amps input. It may be someone put a large voltage on that input.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 12, 2024, 05:18:27 pm
content: Quote from: chilternview on September 12, 2024, 04:57:57 pmOkay I am stupid , I just noticed that the negative rail uses a different pinout VS the positive rail.So all is good. I think.As the master said @EEVBlog "Trap for Young Players .... "

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 12, 2024, 05:22:05 pm
content: Quote from: chilternview on September 12, 2024, 05:13:09 pmF101 and F102 check out ok.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 12, 2024, 05:24:13 pm
content: Quote from: Kleinstein on September 12, 2024, 04:26:22 pmU110 is not hot at all. While the instrument is powered up.

author: iMo
author_rank: Super Contributor
timestamp: September 12, 2024, 05:49:19 pm
content: When the Vcc and Vee of the opamps show +/-18V then the 3.2V serial zener diodes (3pin smd) got shorted (around 3-4 pairs there on the pcb). It happens when you short +/15V somewhere..The 3.2V zeners in series with 18.2V create +/-15V for opamps..

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 12, 2024, 05:49:29 pm
content: input resistors :R104-R110+R180-182+R170-172Checked for cracked joins , all seems good with multimeter measurement though all of them in line.

author: factory
author_rank: Super Contributor
timestamp: September 12, 2024, 05:50:41 pm
content: To me it looks as if this has been worked on before, some evidence of hand soldering and possibly someone used a lot of heat to desolder the 8 pin IC, i.e. too much heat from something hotair based?David

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 12, 2024, 05:52:27 pm
content: Quote from: iMo on September 12, 2024, 05:49:19 pmOP-amps , do you have a name for them ?U110? U201 ? U303?

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 12, 2024, 05:59:41 pm
content: Quote from: factory on September 12, 2024, 05:50:41 pmLooks like it. yes that pin seems to be floating. and not connected anywhere.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 12, 2024, 06:01:55 pm
content: Quote from: iMo on September 12, 2024, 05:56:50 pmI am trying to RT*M. But I am a bit out of my depth as you can see.I am trying to understand what is allegedly the issue. Nevertheless , I will try to figure it out , thanks !

author: iMo
author_rank: Super Contributor
timestamp: September 12, 2024, 06:04:02 pm
content: People here know the 34401 pretty well. So chances are you will get it working..

author: coromonadalix
author_rank: Super Contributor
timestamp: September 12, 2024, 06:32:06 pm
content: you do have the schematics ...http://www.ko4bb.com/getsimple/index.php?id=manualstype 34401a in the search box and magic loll

author: chilternview
author_rank: Frequent Contributor
timestamp: September 12, 2024, 06:40:16 pm
content: The error numbers are saying the ohms function is broken, check Q202-Q211, U201 and CR201/202.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 12, 2024, 09:34:52 pm
content: Quote from: coromonadalix on September 12, 2024, 06:32:06 pmI got the schematics from keysight directly.... as service manuals and user manual. I can't expect them to be different direct from source.Allas I will check you the link , Thank you.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 12, 2024, 11:39:24 pm
content: if you have them that's okthe worst from the bubble would be vias, they could have snapped open, and be very careful not to overheat parts before removali've seen some, drilling an hole where there is no parts and filling the space with superglue while giving some pressure on both sides, to bring back layers together and slimming down the bubble expansion ... but not sure if i would try this, it does seem recoverable, and it could continue to work finepatience and be meticulous ... you'll get it repairedi hope the special asic has not been damaged ....

author: Smokey
author_rank: Super Contributor
timestamp: September 13, 2024, 12:48:23 am
content: The light-through-the-board photo makes it look like a 2 layer board (with no ground plane??). That should be easily fixable in this case. Just need to reconnect top to bottom, and don't need to worry about inner layer connections for the vias. lucky.

author: chilternview
author_rank: Frequent Contributor
timestamp: September 13, 2024, 12:57:51 am
content: Lets recap, you say DCV is OK, and DCI appears to be so, but continuity is flaky and ohms not at all?And self test gives errors 621 , 619 , 619 , 617, 615, 613 ,612 (you've got two 619s, I guess a typo) - which are AC RMS failing full scale, and all ohms current sources failing? Any more error numbers?That tells you there are two problem areas:- ohms after U101/2. So check Q202-211 and U201,CR201/202 (the +7V ref must be OK if DCV reads all OK).- ACV. Could be anything on the AC schematic page 9-11, but you can apply an AC signal and check with a scope its following the circuit path.It is possible someone's been in there and tried to repair it and not succeeded/given up, so the visual damage may have been caused by the initial fault and has been fixed, or by someone trying to fix the problem.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 13, 2024, 01:02:15 am
content: Quote from: coromonadalix on September 12, 2024, 11:39:24 pmI've checked all of them with my Multimeter they seem ok.if I missed any we will find out soon enough.Now I need to find out a way to test the restI have this but I have no idea under what conditions the system is being tested. 10Mohm in the input ?

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 13, 2024, 01:17:08 am
content: Quote from: chilternview on September 13, 2024, 12:57:51 amThank you very much for your time and support.Yes you are right there is a typo.errors 621 , 619 , **618** , 617, 615, 613 ,612next how should I test said components properly ?Check Q202-211 and U201,CR201/202 ?Are there some expected values ? Do I have to desolder them ?Thanks

author: Kleinstein
author_rank: Super Contributor
timestamp: September 13, 2024, 05:24:05 am
content: One can do a first test in circuit. A common failure mode for diodes and transistors is a short. The DMM diode test usually works OK for this and should also work in circuit here.Form the meaured voltages things are not totally off. There may still be an issue with the protection, especially the diode used JFET.It would make sense to measure the test currents to see which ranges are effected. Ideally one would measure the current directly with just a 2nd DMM and also with something like a LED or 2 or 3 diodes in series to see if it changes with external voltage.

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 13, 2024, 09:32:48 am
content: Hello Unknown,it's a pity that some people don't even reveal their first name. I don't like to cite SUCH alias names, in first placeFrom a closeup of the damaged PCB, I strongly assume, that somebody tried to repair the instrument, using a hot air gun around U110, or the Ohm protection transistors Q203 - Q210, either to replace or re-insert them.That guy used too much heat, also too long, and did not cover the other components, so creating this PCB delamination.It's not clearly visible, but all components inside the area of delamination might have been damaged by the heat, at least all the solder joints are under suspect.Please make a macro photo exactly vertical above this area, so that every component and solder joint is sharp, and better illuminated, maybe from different sides.The transistors have been soldered very badly, and I see solder balls. The transistors might be defective, or there might be a short to GND as well , via Q211 which should be tested in situ.If you select 4W Ohm, do you measure the appropriate test currents out of + Input and - Input for the different (manually selected) ranges?You have to de-solder these transistors anyhow, so you can test them individually, later on.W/o the transistors back in place, you might then solder a short from Q202 to CR202 temporarily, to make further tests on the Ohm mode.Descriptions how to do that, has been written down elsewhere .. I guess you found that thread already, as you copied the OHM schematic here.I guess, that U110, that is used for current mode protection, has been replaced, but that mode should work properly, and has nothing to do with your OHM problem. Anyhow, many of the solder joints look very bad. U304 also looks bad.We will definitely continue analysis, when you have presented further results.Frank

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 13, 2024, 05:11:00 pm
content: Quote from: Dr. Frank on September 13, 2024, 09:32:48 amDear Dr. Frank ,Regarding the screen name is a long story but it showed my superficial and lack of deep knowledge of the subject.I took my time with the pictures and its WAY WORSE than I ever imagined.please have a look and we will iron out the details later.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 13, 2024, 05:11:40 pm
content: More pics

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 13, 2024, 05:14:10 pm
content: more

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 13, 2024, 05:14:56 pm
content: more

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 13, 2024, 05:17:16 pm
content: last batch I promise

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 13, 2024, 05:23:17 pm
content: Quote from: Dr. Frank on September 13, 2024, 09:32:48 amIf you select 4W Ohm, do you measure the appropriate test currents out of + Input and - Input for the different (manually selected) ranges?-- What do you mean exactly ? IF the instrument measures the proper value of a plugged in resistor ? no. not at all. you want me to plug a multimeter in mA mode and measure the output current between the LOW + and - ?W/o the transistors back in place, you might then solder a short from Q202 to CR202 temporarily, to make further tests on the Ohm mode.Descriptions how to do that, has been written down elsewhere .. I guess you found that thread already, as you copied the OHM schematic here.I was also a bit in the dark as I didn't really grasp what that schematic meant , and under what conditions the instrument was under .. so I would like some further insights from you if you have the chance. Thanks

author: inse
author_rank: Super Contributor
timestamp: September 13, 2024, 05:36:47 pm
content: That is a somewhat botched repair (attempt).Someone with too much hot air and little intuition had been at work.But don’t worry, with love, patience and enamel wire it can all be fixed.First I would remove the SO8 chip to check where the traces went, then restore missing ones with enamel wire.Use flux to reflow the other components.

author: Sorama
author_rank: Frequent Contributor
timestamp: September 13, 2024, 05:55:20 pm
content: Why not replace all those visibly “impacted” devices by default ?Takes 10’ of soldering.That would also allow one to clean and inspect the pcb.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 13, 2024, 05:59:34 pm
content: Quote from: Sorama on September 13, 2024, 05:55:20 pmDue to the fact the PCB is so badly delaminated , I want to do the bare minimum to reincarnate the device. as far as I know if I whisper a bit louder it would break everything else that might be kind of working.So I am trying to do as much testing and diag BEFORE loading the parts canon.Thanks

author: wraper
author_rank: Unknown
timestamp: September 13, 2024, 06:10:11 pm
content: I'm 99.9% sure someone fried it with hot air so much that melted front/rear switch and water vapor popped the bubble in PCB. As already mentioned the main concern is vias. As there does not seem to be any traces on internal layers, worst case broken vias can be fixed by running thin wires through them and soldering on both sides.

author: m k
author_rank: Super Contributor
timestamp: September 13, 2024, 06:11:31 pm
content: Some joints in between bad ones seem to be fine.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 13, 2024, 06:15:26 pm
content: Quote from: The_Spectrum.A_idiot on September 13, 2024, 05:23:17 pmYes use a different DMM (could be even handheld, no high accuracy needed) and measure the current between the COM and +input, when in the different ohms ranges. Ideally this could be 4 wire mode, but 2 wire mode would likely give the same result.If there is a defect, the current is often way off, like essentially not current. The results can give more of a hint on where the problem is.Though likely not a problem, another simple test is to check for the input bias current in voltage mode. To high a current there can also cause trouble in the resistance measurements. For a final check of the meter one should do that test anyway. For this test there are 2 ways: the simple is uning the 10 M input resistance mode and something like manual 1 V range to compare the reading with a short and open input. The difference should be well less than some 50 pA*10 M = 500 µV.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 13, 2024, 08:56:15 pm
content: Quote from: Kleinstein on September 13, 2024, 06:15:26 pmWith a Fluke 117At A mode DC and AC I get nothing on the 2 jacks HI-LO going though all ranges of 2W AND 4W MODEAT mV DC I get nothing on 2 jacks high and low both on 2W and 4W mV AC I get a fixed 150-80mV AC I will get my better meter 287 and I will retry.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 13, 2024, 09:08:55 pm
content: Okay good news .After re-touching the CR203 Q201 and Q202 Continuity is perfect know , Diode mode has issues show 0.4 instead of 0.6V F-v of a diodeSo I think it's safe to retouch everything with A LOT of flux and see how it goes.Thanks

author: Kleinstein
author_rank: Super Contributor
timestamp: September 14, 2024, 08:21:00 am
content: The current to look at from the ohms source should be DC from 0.5 µA to 1 mA, depending on the range. Beside the current source part, that is also a chance that a realy is at fault. One could check this by taking the current off CR202 instead of the + input.No current may also be faulty fuse at the external DMM - so maybe check the continuity.The already "repaired" area needs to be cleaned anyway - so a touch-up with new flux can be worth a try.If the resoldering changes things it may be woth to re-measure the voltages (to GND) at Q202, e.g. in the 1 K range, both with the terminals open and shorted. This should give a good idea if the issue is more with the actual current source of the protection.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 14, 2024, 09:06:09 am
content: Quote from: Kleinstein on September 14, 2024, 08:21:00 amI think my 117 has no ability to measure so small currents.I need to test it out with 287.Thanks

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 14, 2024, 02:00:39 pm
content: Quote from: Kleinstein on September 14, 2024, 08:21:00 amokay tested with the 289.0.57-0.5μADC on any scale ohms.the areas in question are cleaned and seem ok.**If the resoldering changes things it may be woth to re-measure the voltages (to GND) at Q202, e.g. in the 1 K range, both with the terminals open and shorted. This should give a good idea if the issue is more with the actual current source of the protection.**Are there any expected values ? so set manual omhs , at kohms range , short low and hi ( red and black connectors )I will post my findings

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 14, 2024, 02:30:36 pm
content: Quote from: Kleinstein on September 14, 2024, 08:21:00 ambased on this -see attached-----------////////////---------------kohms - shortR201 4.993vR202 6.972vU201-A 3 - 6.972vU201-A 2 - 6.972V+7REF - 6.972VQ201-1 - 11.099Q201-2 - 7.110Q201-3 - 4.4636CR203-A 1 - 13.594CR203-A 3 - 18.8111SRC Q202 - 1 12.415Q202 - 2 - 1.2771R290 - Q202 - 3- 18.008CR201-A -3 - 18.008CR201-A -1 14.006U201-B 6 11.925U201-B 5 11.098

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 14, 2024, 02:39:27 pm
content: Quote from: Kleinstein on September 14, 2024, 08:21:00 am**If the resoldering changes things it may be woth to re-measure the voltages (to GND) at Q202, e.g. in the 1 K range, both with the terminals open and shorted. This should give a good idea if the issue is more with the actual current source of the protection.**openQ202-1 - 12.416Q202-2 - 3.4-3.45Q202-3 - 18.006shortQ202-1 - 12.416Q202-2 - 1.2460Q202-3 - 18.006

author: Kleinstein
author_rank: Super Contributor
timestamp: September 14, 2024, 06:14:11 pm
content: The full 18 V at the Q202 gate suggsts that the regulation tries to turn the fet off (it is a P channel FET and thus off with a positive voltage).The voltages at the OP-amp inputs (pins 5 and 6) suggest that the output should go negative and not positive as observed. So chances are high that U201 B is bad.Still having some voltage at the output side (Q202 pin 2) of the curren source somewhat points to leakage at Q202 - so this part may also be damaged ( I would at least order or look for a replacement, if ordering an AD706 (or substitute).This leaves the question if the protection is working OK. This could be a shorted transistors, or maybe one with too low a break down votlage and also an open Q211. Off cause the reason of the damage could also be from just too much voltage for the transistors.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 14, 2024, 08:39:41 pm
content: Quote from: Kleinstein on September 14, 2024, 06:14:11 pmDear Mr. Kleinstein Thank you so very much for your input and help,Started Loading the parts canon.Q201 - MMBF4392LT1G VS MMBF4392Q202-MMBF5461 - is unobtanium. I am trying to find something similar.Q211 - MMBF4117 VS MMBF4117AU201 - AD706JRZ the closest candidate VS AD706JRQ203-210 - MMBT6520LT1G VS MMBT6520LCR203 - BZX84-C5V1-QR VS BZX84C5V1CR201 - BZX84C4V7-E3-08 VS BZX84-C4V7Lets hope I will manage to pull this offAny input on parts selection is always welcome

author: Kleinstein
author_rank: Super Contributor
timestamp: September 14, 2024, 10:06:12 pm
content: For the P-JFET the MMBF176 should be OK - one of the few P-channel fets that are usually available.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 15, 2024, 08:47:10 am
content: Quote from: Kleinstein on September 14, 2024, 10:06:12 pmFor the Q202 right?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 15, 2024, 08:58:47 am
content: The mmbf176 would be my suggesting for Q202. There is not that much choice if p-channels JFETs anyway. The speed and thus to a large part the capacitance should not matter much. The mmbf176 has roughly a similar threshold and Idss to the MMBF5461. The voltage rating should be sufficient for the use case.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 15, 2024, 09:28:32 am
content: Quote from: Kleinstein on September 15, 2024, 08:58:47 amMMBFJ176 you mean?https://eu.mouser.com/ProductDetail/512-MMBFJ176Many thanks

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 18, 2024, 10:52:22 pm
content: Dear AllAll the parts arrived ,Now I would like your recommendation for the hot air station setup , how should I go hot and high output to remove the components fast ? or slow/ medium heat , medium flow and take my time and slowly ramp up the temperature until the solder liquefies ? Big , small nozzle ?lastly I will kapton tape everything around that area and hope for the best , lots of flux , and hope for the best.Let me know if you have any other tips and tricks how to deal with hot air .Thank you in advance

author: wraper
author_rank: Unknown
timestamp: September 18, 2024, 11:27:57 pm
content: All of that can be soldered by dual wielding soldering irons, soldering tweezers or using low melting point alloy. I would avoid using hot air on PCB that already popped as much as possible to minimize chances of further damage.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 19, 2024, 07:19:40 am
content: Dear All ,We kind of made it , now I have 2 errors. 612 and 618.replaced :U201Q202CR201Q202-210Q201Q211CR203Q202What now ?Thank you for your help in advance

author: Kleinstein
author_rank: Super Contributor
timestamp: September 19, 2024, 07:28:42 am
content: From the description the errors 612 and 618 are essentially the same, a problem with the 500 nA current source or 10 M divider.A way to check is to measure the 500 nA current externally. If needed with a resistor and voltmeter.Another point to check could be the resistor readings for the 10 M range (e.g. check 1 M and 4.7 M).

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 19, 2024, 04:42:43 pm
content: okay so shorting and measuring the μA output :000. ohm range -999.4 μA0.1k range - 999.3μA00.1k range -99.46μA000.1k range -9.81μA0.1M range -4.83μΑ00,1M range - 0.41μΑ000,1Μ range -0,42μΑ

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 19, 2024, 04:46:18 pm
content: Quote from: Kleinstein on September 19, 2024, 07:28:42 amA 10K 1/4w 5% resistor measures 09.912 kohm on auto-ranging

author: Kleinstein
author_rank: Super Contributor
timestamp: September 19, 2024, 05:32:04 pm
content: 410 / 420 nA should still be just inside the acceptable range for the current source.It is still be a bit odd that the current is that far off nominal. This could be leakage (e.g. not yet cleaned flux), or maybe extra bias from the OP-amp. If the issue is leakage it may get worse with higher voltage / higher resistance. A test would be to check the linearity with a series connection of 1-2 M resistors in the 10 M range.Another possible point of failure may be the relay connecting the 10 M divider. Is the 100 V range working reliable ? For a test, e.g. check something like a 9 V battery in the 10 V (high Z) and 100 V range and switch between the 2 ranges a few times.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 19, 2024, 06:22:13 pm
content: Quote from: Kleinstein on September 19, 2024, 05:32:04 pmUsed a 9V PSUTried every range on VDC and values don't change.re measured μΑ on ranges after cleaning the flux and doing the range change.Results :000. ohm range -999.1 μA0.1k range - 999.3μA00.1k range -99.46μA000.1k range -9.84μA0.1M range -4.83μΑ00,1M range - 0.36μΑ **000,1Μ range -0,36μΑ **Quote from: Kleinstein on September 19, 2024, 05:32:04 pmHow can I do thins without a reference resistor ?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 19, 2024, 06:42:23 pm
content: With little difference at 9 V this suggests a woking relay.Getting less current after cleaning suggests that the cleaning may have made things worse, e.g. leaving moisture or more conductive film at the critical areas. Another possibility could be semiconductor leakage (e.g. at Q211) and a higher temperature for the 2nd test.One could look at how the current changes with temperature: leakage in semiconductor usually goes up with temperature quite fast. Surface leakage from dirt on the PCB tends to get down with temperature or at least not up very much.For a linearity test it does not need very accurate resistors. The deviation from the current is rather large, reaching some 10-20%. So the resistors only need to be reasonabel stable to maybe 5% between the tests. So more normal (e.g. 5 or 10% tolerance, though maybe not use cabon film) resistors should do and the exact value does not matter. It is just to reach a sum in the 8-11 M ohm range.The basic version would be comparing 2 x 4.7 M in series to the sum of the individual measurements in the 10 M range.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 20, 2024, 05:30:05 pm
content: Quote from: Kleinstein on September 19, 2024, 06:42:23 pmok finally got around to get it sorted,So with a 10K resistor at 10K range manualI get -9.941,10 kohmswith 1x 4.42K @ 1% I get 4.429,57 kohmswith 2x 4.42K @ 1% I get 8.848,81 kohmsat 000.1K range I getwith 3x 4.42K @ 1% I get 013.053,2 kohmsThanks

author: Kleinstein
author_rank: Super Contributor
timestamp: September 20, 2024, 09:11:44 pm
content: The 10 K range looks like it works. To check if the sum really works Ok one would need to measure both resistors separately to really add the numbers. The expected difference that may show up would be in the 6 th maybe 5 th digit.For the problem with the low current one would need to do the similar test with larger resistors, like 4.7 M or a chain of 6-8 x 1 M. The 10 M range where a larger error is expected.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 20, 2024, 09:27:22 pm
content: Quote from: Kleinstein on September 20, 2024, 09:11:44 pmOkay lets say hypothetically , all these tests show that we are kind of working, in certain / most ranges.is there a chance to even calibrate and keep the instrument error free ? or this is just a sanity check to make sure that we are measuring true regardless if the instrument is not passing it's self tests ?Do you think was a mistake that I've changed every components all at once ? and most probably some components are not "matched" per say ?Just so that I would know IF i have to live with it or hope for a trustful futureBecause is all about trust. If I can't trust it , I can't use it.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 20, 2024, 09:39:31 pm
content: that's why you use the meter self tests. if it fail you have a problemand when you don't get any fails, the ultimate answer reside in dmm calibration, and you'll know it is perfectBut i'm not sure how the self test may handle bad calibration, or out of calibration ??and just a comment, for future(s) purchase(s) if any, always ask to see an passed self test picture, or ask the seller to do it

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 20, 2024, 09:44:09 pm
content: Quote from: coromonadalix on September 20, 2024, 09:39:31 pmI agree. It was a kind of deceptive practice as he listed it as {tested good} and at the very bottom of the description, 'continuity and resistance not operable' ... and you guest it I found out to read the fine print before looking as good deal.On his defence it was mentioned. I didn't read it.Anyway lesson learned. Now back to trying to get this **** working.I would like to thank everyone for their help and input I very much appreciate it !!Regarding bad calibrations well I've changed components that were supposed to be paired and verified with other non paired but original close enough components.whether or not a proper full calibration will make/force the meter to pass it's self tests as at the moment in essence I don't have any faulty components that I hope someone will let us know.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 20, 2024, 10:49:06 pm
content: The parts that were replaced don't need to be paired and most of them should not even effect the calibration / scale factors. From the changed parts it is only the offset of the OP-amp that has a small effect on the scale factor of all resistance ranges. The OP-amp bias and leakage currents can also effect the high resistance ranges (10 M + 100 M and a little 1 M) . The others should not be effected enough to get much of an error.It looks like the PCB is not yet fully clean / dry. If there is some conductive flux residue or similar it can take quite some cleaning to get rid of the leakage.Worst case there is leakage from the overheated PCB part or dirt inside the bubble.one may have to close the case for the tests, so that light would not effect some of the SMD parts - some can be a bit light sensitive.Changing all the parts was not such a bad idea. The OP-amp was very likely bad from the tests and the other parts are not that expensive and possibly damaged.The voltage and current ranges should not be effected by the repair, unless there is PCB contamination.There are a few additional tests that one can do with relatively little effort / instruments to check a few more points no checked so much in the self test.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 21, 2024, 06:07:33 am
content: Quote from: Kleinstein on September 20, 2024, 10:49:06 pmokay , I will try to clean as much as possible under the IC and around it ( Isopropyl and contact cleaner might do the trick ? )I guess giving the whole PCB an ultrasonic bath would be a big no. no I assume.I will get more resistors and see if I can get the reset fo the tests done.Thank you very much

author: coromonadalix
author_rank: Super Contributor
timestamp: September 21, 2024, 06:09:07 am
content: same here, you solved many errors, maybe another cleanup with better products, contact cleaner must not leave any residue or oil / lubricantand maybe, just maybe try to get better resistors values as kleinstein wrote to tests all possibilities, and slowly redo all the tests / current generator etc ..this meter has gone thru a lot, be sure the front and rear switch is good too, it can play some tricks, there was some who had relay problems on one coto model ...be patient and do things methodically, you'll get there, and lucky you schematics are known ...

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 21, 2024, 06:11:36 am
content: You can say that again indeed this poor instrument had a very harsh life.But yes step by step hopefully I can get it back to spec.

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 21, 2024, 02:37:46 pm
content: sorry to reply so late.The current source still might have a problem gor the high Ohm ranges. That should be the 500nA source current, affecting both highest ranges.Please apply a 1M or 10M resistor in 2W autorange mode, and fill out the diagram, which shows the crucial voltages in this circuit, once with the correct ones as measured by me.Most suspect is this dual OpAmp with very low bias current, which fails quite often.Frank

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 22, 2024, 08:00:55 pm
content: Quote from: Dr. Frank on September 21, 2024, 02:37:46 pm1M resistor : 0.9953mohms on fluke 289on instrument : 0.959,20 =mohmsR201 4.993vR202 6.972vU201-A 3 - 6.972vU201-A 2 - 6.972VU201-A 1 - 3.8189V+7REF - 6.972VQ201-1 - 8.896Q201-2 - 7.113Q201-3 - 3.8189CR203-A 1 - 13.974CR203-A 3 - 18.8101SRC Q202 - 1 - 8.920Q202 - 2 - 5.965R290 - Q202 - 3- 10.406CR201-A -3 - 10.406CR201-A -1 - 5.667U201-B - 7 - 5.670U201-B - 6 - 8.926U201-B - 5 - 8.901Thank you in advance

author: Kleinstein
author_rank: Super Contributor
timestamp: September 22, 2024, 09:03:34 pm
content: The votlages at pins 5 and 6 of U201 are a bit different, but this is likely from the loading from the DMM to measure these voltages. The voltages look reasonable.Being some 4 % off with the 1 M resistor supports that the test current is too low. Maybe try if the reading drifts just after turn on / warm up. If the issue is from leakage in the semiconductor, it is suspected to get quite a bit worse (like 2 x the leakage) with warm up. With leakage from a dirty PCB less temperature effect is expected.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 22, 2024, 09:34:31 pm
content: Quote from: Kleinstein on September 22, 2024, 09:03:34 pmWell I didn't leave the instrument warm up with its covers on for 5h. ( I don't have such time on my hands)The pcb was cleaned with IPA as best as possible. Next step is to use high pressure contact cleaner to get under every IC and diode ( i can't imagine any other way to get under that clean.)I am hoping for Dr. Frank to give some insight to what might be at fault. I am almost certain that some componet I selected is not appropriate. And I should had just changed the OP AMP only.never the less, time will tell.If further warmup is needed I will do such test with different resistors becuase the 1M was the biggest I had in my arsenal at the moment.Thank you in advance

author: Kleinstein
author_rank: Super Contributor
timestamp: September 23, 2024, 06:23:16 am
content: The current is rather far off, well more than expected for leakage at Q211 or Q202 or the OP-amp bias current. The transistors in the protection would not effect the low current, even if bad or broken.A point could be if the OP-amp is genuine or a Ebay/Ali part.The change in current from doing the extra cleaning step points strongly towards a dirt problem, though it could still also be a thermal effect (e.g. higher temperature in the 2nd test).No need for a full warm up test. The first half hour should show most of the thermal effect.Contact cleaner may or may not be suitable, as some include lubricants and can leave a resudue. They may also not be good solvents, but more a thing to remove oxide layers. A spray can can also contaminate other areas from splatter. HIgh pressure is more a thing for cleaning a whole board, not so much for loacal claning. That is more a thing for brush, seringe and tissue.One can still use IPA or similar around / under the chips. It will flow also under the chip and can be sucked out / wicked out with clean tissue. The dirt is removed by the solvent removed, not by the solvent added.IPA is also only good for some contaminations and there are different purities / grades. More salt like contaminations are better removed with water or a IPA / water mix. More organic / grease like dirt would want high purity / low water content IPA or even a different solvent. It may well need multiple cleaning steps. Usually water or a water+IPA mix first and at the end clean IPA.One could try / test cleaning of flux residue on a different PCB. So do experiments separate first, to see what works with the flux that was used in the repair. For the flux the soldering step can change things - heated flux is different from fresh or only partially heated. Not all residue from the flux is actually bad - some contain some parafin / wax component, that is hard to remove, but isolating.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 23, 2024, 08:22:56 am
content: All parts are from mouser. I would never get ebay parts unless are unoptenium.But what ever I changed / replaced are original mouser parts.All replaced with soldering iron and soldering wick.Flux I have a syringe ( i need to find the brand name I can't think of it on top of my head)Cleaning, before soldering anything on I cleanred the area and pads after wicking them with IPA and a q-tip ( the thing used (incorrectly) for ear canal cleaning) and then soldering on the parts 1 by 1 ( 1 leg at a time)Let me know.Thank you in advance

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 23, 2024, 07:17:16 pm
content: Flux Type : SMD291/30CC - Chip Quik

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 24, 2024, 01:56:57 pm
content: Quote from: The_Spectrum.A_idiot on September 19, 2024, 06:22:13 pmThe reference currents are all still n.OK, i.e. about 140..180nA too low, which is clearly visible for the 500nA, 5µA, 10µA and probably also for the 100µA reference currents.That's the reason, why you get ERR 612, 618, which both indicate a failure of the 500nA current, i.e. out of tolerance.U201 was really defective, as initially none of the expected voltages @ pin5, 6 were ok, instead showing the usual faulty values for too high bias currents, i.e. broken input stages.Now you have to search, where these about 180nA are flowing to GND.Hopefully your new U201 is OK, then Q211 would be the next suspect. So let's at first rule out both these failure modes:Please desolder CR202, and then measure the reference current directly in situ towards AGND, i.e. from pin 3 / collector of Q209 to AGND, which is @ INPUT LO.you might check for the lower currents of 500nA, 5µA and 10µA only, so you have to select 10M, 1M and 100k ranges (see page 98 of service manual). An external resistor is not needed.Please compare these three currents with those you have measured in the above table.Frank

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 24, 2024, 02:47:17 pm
content: For evidence, I measured the currents of my 34401A:100, 1k range: 1.0003 mA (+0.03%)10k range: 99.898 µA (-0.10%)100k range: 9.9858 µA (-0.14%)1M range: 5.0198 µA (+0.4%)10M range: 501.66 nA (+0.3%)Therefore, the 3 highest currents are about 0.1 .. 0.2% within nominal, and the 2 lower currents are about 0.5% within nominal, so that's the ballpark what to expect as being OK or nOK reference currents.To be more precise: The nominal values of the currents should be within about 0.5% consistent, relative to each other, as an additional +/-2% for the LM399 voltage reference (6.95V nominal) has to be taken into consideration.For my 34970A, I found these currents:100, 1k range: 0.9877 mA (-1.2%)10k range: 98.712 µA (-1.3%)100k range: 9.8962 µA (-1.0%)1M range: 4.9341 µA (-1.3%)10M range: 494.3 nA (-1.1%)Frank

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 24, 2024, 03:30:51 pm
content: CR202 Removed;Measurements still the same :00,1M range - 0.36μΑ000,1Μ range - 0,36μΑnext step ?

author: mawyatt
author_rank: Super Contributor
timestamp: September 24, 2024, 03:44:19 pm
content: Out of curiosity we took a quick look at our HP34401A and AG34401A {readings}. These were acquired years ago with unknown history and aren't used much these days, and never properly calibrated since acquired.1.001484mA {1.001779mA}100.3637uA {100.0724uA}10.00111uA {10.04446uA}4.99031uA {5.026583uA}497.396nA {503.761nA}BTW the above Dr Frank post obviously should be 501.66nA not uA on the 10M range.Best,

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 24, 2024, 03:45:52 pm
content: what about 1M and 100k ranges?Next step: Please remove Q203 and measure these 3 currents from pin 2 of Q202 to AGND / INPUT LO.Frank

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 24, 2024, 03:53:50 pm
content: the rest of the ranges measure same as before.okay.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 24, 2024, 04:05:04 pm
content: Quote from: Dr. Frank on September 24, 2024, 03:45:52 pmQ203 removed and cleaned everything flux coatedresults :'(pin 2 of Q202 to INPUT LO000. ohm range -997.6 μA0.1k range - 997.6μA00.1k range -99.38μA000.1k range -9.89μA0.1M range -4.92μΑ00,1M range - 0.35μΑ **000,1Μ range -0,34μΑ **Thank you in advance

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 24, 2024, 04:20:32 pm
content: Ok, please re-insert CR202 and Q203. You might then test these currents on the outside (Input Lo / Hi) again.Have you tested the old components, Q203-Q210, Q211, Q202 and CR202 if and how they had been damaged?If these parts are all damaged there had been a very high overvoltage event, which could have affected U201-B, but also C210 and U101-E.So my next guess would be to remove or replace C210, that's a 0805 ceramic capacitor .. I don't know if it's a special type for low leakage currents..It's a COG / NP0, which usually has better insulation than X7R. You might check this components outside for leakage, when applying 20V in series.Have you got a genuine, new AD706?Frank

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 24, 2024, 04:41:01 pm
content: Q202 I was in between what component to selectI was between :https://eu.mouser.com/ProductDetail/512-MMBFJ176(this one is installed)andhttps://eu.mouser.com/ProductDetail/106-SMP5461I will reinstall the rest and order the capacitorIf U101 is broken I should assume that this is the end of this journey right ?Thank you in advance

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 24, 2024, 04:42:41 pm
content: Quote from: Dr. Frank on September 24, 2024, 04:20:32 pmI got this from mouser.https://eu.mouser.com/ProductDetail/584-AD706JRZNo ebay or unknown source components.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 24, 2024, 04:45:41 pm
content: Quote from: Dr. Frank on September 24, 2024, 04:20:32 pmregarding the C210this is what the service manual said about it :C210 0160-5954 4 Capacitor-Fxd 220 pF ±5% 50 V 04222 08051A221JAT AThis is the closest I can findhttps://eu.mouser.com/ProductDetail/KYOCERA-AVX/08051A221JAT2A?qs=j3sIhLrTlovso9JF71DsEg%3D%3D

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 24, 2024, 04:49:52 pm
content: Quote from: The_Spectrum.A_idiot on September 24, 2024, 04:41:01 pmThat JFET should Q211 should be fine, but I meant U201, if you bought a genuine AD706, or have you picked another type?Please first remove C210, maybe the OpAmp will not oscillate, and you can test the currents, before ordering.If U101 is damaged, you might be able to re-calibrate the Ohm ranges, which would then compensate for the additional leakage currents.I expect that up to 1MOhm range, it will still work ok, 10M and higher might be unstable (over temperature, time), and maybe you will not be able to calibrate these upper ranges properly.DCV seems to be ok, but you will always get these Test Errors 612, 618, because the 500nA current is outside of tolerance.If you can live w/o the higher Ohm ranges, your 34401A might be still quite usable, but it needs a full check of all ranges and modes.Frank

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 24, 2024, 04:53:21 pm
content: Quote from: The_Spectrum.A_idiot on September 24, 2024, 04:45:41 pmThat's perfect. But please, check the OpAmp and w/o C210 , before ordering.Maybe it's the wrong OpAmp (low bias type!) or you test another sample first.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 24, 2024, 04:58:12 pm
content: Quote from: Dr. Frank on September 24, 2024, 04:53:21 pmhttps://eu.mouser.com/ProductDetail/584-AD706JRZthis is the OP-AMP Ι could find.Wιthout the C210 current when up to 0.44μΑWaiting on your response.

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 24, 2024, 05:04:47 pm
content: and the other currents, 5µA and 10µA?Does it now pass the test?That means, DIP 8 is obsolete, and you have used an SOIC / DIP adapter? Or was it an SO package initially? I don't remember..This type is correct, anyhow

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 24, 2024, 05:09:11 pm
content: Quote from: Dr. Frank on September 24, 2024, 05:04:47 pmLet me solder everything back except the cap and see how it goes.

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 24, 2024, 05:10:43 pm
content: Great!I have to leave for basketball in 20min., so maybe I can't answer your questions later.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 24, 2024, 05:18:16 pm
content: still Failed. ( I soldered everything back as they were. )I managed to find on ebay original OP amps.Let's hope this is the case.(changing to an original part)Thank you for your time !

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 24, 2024, 05:21:55 pm
content: Quote from: Dr. Frank on September 24, 2024, 05:04:47 pmWell I managed to solder it on .. regardless if it was a different package ... pinout was the same so I just made due.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 24, 2024, 05:52:24 pm
content: A damaged capacitor C210 is possible, e.g. due to PCB stress from the bubble. For a test one could try without or with a different low leakage type, possibly also through hole and a slight larger values like 330 pF. C0G capacitors should be reasonable low leakage, also for more normal types.With the flux it is also possible that just re-soldering effects leakage on the PCB. The flux linked should be easy to clean and at least for a first test should even be OK without extra cleaning. Excessive flux that did not got hot may however be a problem and likely needs cleaning.The AD706 should still be available and the photo shows a SO8 foot-print, not a dip. For the wide / narrow version one often can bridge the gap, though this can make PCB cleaning a bit more tricky.

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 24, 2024, 09:30:08 pm
content: Quote from: The_Spectrum.A_idiot on September 24, 2024, 05:21:55 pmThat's sub optimal. Please have a closer look for possible contamination or solder bridges, with your nice microscope

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 24, 2024, 09:32:31 pm
content: Quote from: Dr. Frank on September 24, 2024, 09:30:08 pmThank you for getting back to me ,Well I will have a look , but I don't have much hope. ( it was pretty flush with the PCB )If that ends up to be a dead end. what are other possibilities ?Thanks

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 24, 2024, 10:01:28 pm
content: you might replace U201 with another sample, maybe you created an ESD damage when assembling the new component.And as said, I assume you can use the instrument with a fresh calibration in most modes / ranges.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 24, 2024, 10:11:19 pm
content: Quote from: Dr. Frank on September 24, 2024, 10:01:28 pmOkay , hopefully I will be able to pull it of in an ESD safe environment ,I bought off ebay original agilent part number parts. Hopefully by next week they will be in my possession , If I can't find a solution for this I will most probably just swap the original part and then send it for calibration and hope that they can calibrate it in fault mode. ( I think they are not accepting devices for calibration and certification if they fail any of the self tests ... am I correct ?Thanks

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 24, 2024, 11:26:03 pm
content: IT PASSED !!!!After re-checking every solder joint , every flux residue , anything and everything on the PCB.3 things.Dr.Frank - Thank you for everything for all the valuable advice and helping me every step of the way !!! the IC being the wrong footprint and pointing that out put me into thinking !!Kleinstein - You were right andI waswrongthere was some pesky flux hidden under the IC so contact cleaner and IPA and passing KIMTECH wipe under the IC for 1h it finally workedEveryone else that spend time helping me out and pointing out obvious things that I didn't know and helped me through eveything step by step I would like to tell you a huge thank you !!Now off to calibration house!!! Hopefully they won't need and arm and a legThank you in advance for your help , for your time , and your patience !!!The Spectrump.s.: The Ohms values :Results :000. ohm range -997.0 μA0.1k range - 997.0μA00.1k range -99.44μA000.1k range -9.98μA0.1M range -5.00μΑ00,1M range - 0.52μΑ000,1Μ range -0,52μΑ

author: coppercone2
author_rank: Super Contributor
timestamp: September 25, 2024, 01:28:46 am
content: is that guy on the left George washington??

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 25, 2024, 02:01:28 am
content: Quote from: coppercone2 on September 25, 2024, 01:28:46 amNo.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 25, 2024, 02:25:53 am
content: wow totally UN-apropriate to bring this hereis this how you end your repair thread ?

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 25, 2024, 02:28:22 am
content: You are right.It was wrong.When I am happy sometimes I go above and beyond.Sorry about that.

author: coppercone2
author_rank: Super Contributor
timestamp: September 25, 2024, 02:30:20 am
content: its not a bad analogy how it hides under ceramic and prevents a system from functioning and its hard to get out

author: Kleinstein
author_rank: Super Contributor
timestamp: September 25, 2024, 05:04:10 am
content: I would still wait a little before sending the meter out to calibration. One point is waiting for settling after the disturbance from soldering. There is likely PCB stress and a disturbed humidity and this can cause some drift for the next few days / weeks. Just after a repair there is also a slighly increased chance to get another defect, a little like with a brand new meter.Another point is first doing a few more checks to see if the meter really works. There may be other, less visible defects / problems.A relatively easy part to check is the input bias current, e.g. in the 10 V DC range. This can be checked from the rate a low leakage capacitor of some 10 nF charges or discharges.Another point can be the drift during warm up. Excessive drift could point to a hidden defect. Here one may need some stable reference, so not so easy a test.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 25, 2024, 03:24:42 pm
content: Another question for the experts ,I spoke with 2 labs today.1 was recommended by keysight1 is a local lab.The recommended keysight lab said that will verify the instrument and all its functions , will give a certificate of calibration. BUT if any of the functions have any deviation will give a limited certification with a deviation factor. I would like to know if this is standard OR I didn't convey my thoughts to the guy at the other end of the line correctly?In my mind calibration means that I am forcing the instrument to measure a known thing and replace whatever value its measuring with the proper one.so IF I am measuring a 1M standard that is 1ppm and the instrument is 40ppm and the instrument measures 0.98M then by calibrating the instrument means I am making modifications via the software to force the meter to get the measurement from 0.98M to 1M and adjust whatever values are wrong in its memory to account for age and wear and tear , then I am testing the linearity of the instrument. If all goes well means the correction was successful.As far as I understand what they provide is just a proof testing that indeed the instrument is measuring what is real +/- the allowed deviation or error from the datasheet. And just say that this instrument is measuring the values as close to reality. Nothing else.Is this what calibration means in the real world ?The local lab asked me to email them the datasheet and instrument brand and model and they will get back to me. (most probably won't be able to verify it leat alone calibrate it in the way I have it in my mind)Let me know if there is a better way to ask what I have in mind.Thank you in advance for your timeThe Spectrum.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 25, 2024, 04:10:13 pm
content: if the instrument normally pass self tests, you should be able to get a full certificationBUT yes it could pass self tests (i dont know the precision of the internal tests done) and maybe fail if it is at the "out of tolerance" limit or goes beyond that ...and yes you could still get a limited certification, AND accept or refuses it, but fee's can or could be charged to you either way ... (Here in my country they work like that, if it pass or fail)the best would be find some people who can check it BEFORE doing certifications, maybe in the TEA thread some people could help ?yes some wrote, the best would be to run the meter for a few days and try to see if it deviates, even a good cleaning could still leave traces ... re re and re check ... this meter has gone thru a lot ... i mean a lot ... you have to be surethe meter is a good piece of precision, if it goes well, it may or will be precise for many years, i had 3x of them (1 xformer blown, 1 dim vfd, and one fully recapped), the later received a full certification (but frankly it was still in the specs after a decade) ..if the meter do and does precision measurements, you need to get it certified, or if its a "toy" or non precise stuff and nothing depend or need the be certified BY YOUR meter, you can use it like this, but you'll never know unless doing some good checks with precision parts in the 0.5 % 0.05% ... i have Fluke 0.013% precision resistors ...if a local lab ask you specs mmmmmmmm i would not be sure of their capacity ...normally you need Fluke calibrators or else in the 7 or 8 digits of precision

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 25, 2024, 04:18:12 pm
content: Quote from: coromonadalix on September 25, 2024, 04:10:13 pmI will run it the next month , But I need to get some precision resistors , I have a GBID ( that interface ) to capture the readings ( it even has serial ).And maybe use 4W and 2W measurements to test said resistors.The most difficult would be for voltage and current ( as I have no idea what can be that stable while measuring it , a battery is out of a question )Because they said their stuff is still out on calibration aboard.But my question was if this is normal to just verify the instrument and not adjust it via its calibration menu etc etc ...Anyway slowly I will get it done somehow. I will email keysight too what is their normal procedure in case of non conformities ...QuoteMy thoughts exactly ! That's why I will send it abroad.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 25, 2024, 04:23:29 pm
content: it is normal or not upon what use you intend to do with itprecision means calibration / certifications at 1 or 2 years intervalsbasic use means, you do basic or non precise checks but not undergo the cals certsbut at some point you will need to be sure of this meter and it's capacities, at 6.5 digit, it is not a toy ... do you accept to use it not calibrated an live with uncertainties ....i personally would not, it is a 0.035% precision meter if i recall ... or more in the 0,01% in resistances ....

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 25, 2024, 04:26:53 pm
content: Quote from: coromonadalix on September 25, 2024, 04:23:29 pmAs soon as I do it once and I know that is ok, then I can start to trust it.I can repeat the cal every 5 years or so just for my sake , I am not a professional but I want to have confidence in my readings.Thanks we have a similar mind setThank you in advanceThe Spectrum

author: Kleinstein
author_rank: Super Contributor
timestamp: September 25, 2024, 06:23:16 pm
content: If not needed for some professional use the question is if one really needs a formal calibration. Form most hobby use one may not really care that much, though a good test to get confidence is still wellcome.The usualy calibration is just the testing - often without giving the actual readings, but just a pass / fail. The change of the cal constants in the meter is called adjustment and this may cost extra and is rarely done, as long as the meter is still in specs. In my oppinion one should consider readjustment, or a marking on the meter if it comes close (e.g. 75%) to the accuracy limits, as there is also a drift component and the calibration should give confidence that the meter will meet the specs for the next 1 or 2 years.The 34401 are usually quite stable and an re-adjustment is rarely needed.The repair in the ohms section should not have effected the amps and voltage part. The resistor part can be effected a little, from the offset of the OP-amp that was changed. Up to 100 µV offset relative to 5 V would be 20 ppm contribution from the offset and 2 OP-amps in the circuit. For the 10 M range this would be 10 x higher with only 0.5 V ref. voltage for the 2nd OP-amp. In addition the bias / leakage current could be relevant there too. So there is a chance that the 10 M range can be out of spec.The self test is not very strict and does not cover all aspects. From the service manual the last 2 tests that caused an error have a test limit of +-20% for the current - so not at all strict. So it may not trigger on a lesser problem that can still make the meter to fail. Testing to better than 10% is not that hard.One may not need super accurate parts to do some testing considerably stricter than the self tests. Some of the tests also cover things not covered by the self tests and often not checked during calibration. A few tests that can be done relatively easy are:1) input bias with a low loss, low leakage capacitor (e.g. 1-10 nF PP or PS type)2) sum of 2 resistors to check the linearity in the resistance mode (can be effected by leakage). With some care in the environment, relatively common 100 ppm/K parts can be sufficient. For 4.7 M+4.7 M even lower grades can be OK.3) drift during the warm up, especially for zero voltage and resistors4) a turn over test with a 9 V battery or similar. This may need some care to keep the battery undisturbed and repeats to check.5) A check of the noise with a short.6) Check some resistors (e.g. 10K, 100K, 1 M) in 2 ranges each.7) zero resistor readingAC reading in a square wave with accurate amplitude (e.g. CMOS gate with 50/50 ratio)Doing the tests is a way to get familiar with the meter too.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: September 25, 2024, 06:47:29 pm
content: Quote from: Kleinstein on September 25, 2024, 06:23:16 pmThank you very much for the pointers.The reason I am leaning heavily towards calibration and adjustment is the sole reason that the instrument comes from an UNKNOWN environment with unknown calibration verification. No cert has accompanied the meter.So this lack of traceability is the issue.Plus as I said its all about trust.Thank you in advance