HP/Agilent/Keysight 34420A NanoVolt/Micro-Ohm Meter repair - Page 1
Forum section: electronics / repair

author: plesa
author_rank: Frequent Contributor
timestamp: January 02, 2016, 12:05:16 am
content: Multiple months has been under my bench waiting for repair, so lets started.Meter is quite old ( according to serial number made 1995 ).This meter is quite popular for ration measurement compare to 34401A it has low voltage preamplifier which enable 1mV DCV range and low ohm measurement with high precision.- 7½ digits resolution- 100 pV, 100 n? sensitivity- 1.3 nVrms, 8 nVpp noise performance- Built-in low noise 2 channel scanner- Direct SPRT, RTD, Thermistor, and Thermocouple measurementsThanks to absence of fan unit is clean after several years in operation.Compare to competitor (Keithley 2182A Nanovoltmeter) has own current source which enable Ohms/RTD measurement.Meter is still in active production (end of this year will be not possible to ship to EU - RoHS)Price $4445 new one, $1538k unit exchange byAgilentKeysight. Used working unit can be found on eBay for quite high prices ( similar to 3458A), working unit in uknown state should be about $500, with calibration $700-1k.Like 3458A it has been sold by Fluke ashttp://assets.fluke.com/manuals/hp34420xiseng0000.pdffor temperature measurement and calibration.Initial inspection:- Power on and passed self test- VFD display is little bit dim- Input connector has bend pins- DCV channel 1 - not working- DCV channel 2 - OK- 2W Ohms - OK- 4W Ohms - OK- RTD - OKSchematic:http://www.ko4bb.com/manuals/download.php?file=HP_Agilent/Agilent_34420A/Agilent_34420A_SCHEMATIC.pdfUser Manual:http://literature.cdn.keysight.com/litweb/pdf/34420-90001.pdf?id=1000003601:epsg:dowService Manual:http://literature.cdn.keysight.com/litweb/pdf/34420-90010.pdf?id=816987When I tried to fix bend pin I found they are made from pure copper ( not like the regular gold plated LEMO pins ) and are quite brittleSo I needs to order replacement.Replacement we discussedhttps://www.eevblog.com/forum/repair/looking-for-the-input-connectors-for-agilent-34420a/and after this excersise I can confirm that the connector housing is EVP.1S with custom made pins.I do not want to stop repair by this, so I desoldered connector assembly and solder insted of it 50cm of PTFE insulated silverplated wires (made by Habia).After repair meter can be handy for low EMF measurement and ratio measurement of LTZ1000 boards.Any experience with DCV Channel 1 repair may be helpful.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 02, 2016, 01:11:48 am
content: I bought a 34420A that had a defective input channel. I cannot remember which one was defective, but I traced it straight to an optoisolator that wasn't functioning. Looking at the schematics, I think mine was U125. I could see the enable signal being applied, but the ground connection wasn't completing. I was able to jumper pins 4 and 6 to get the DC function working.I would have to open it again to verify which one it was but I would start with those. The replacement was bought at Digikey, I will have to search through previous orders to find it if needed.

author: plesa
author_rank: Frequent Contributor
timestamp: January 02, 2016, 02:03:49 am
content: Thanks for tip, it is the same failure U125. When shorted pin 6+4 Channel 1 DCV reading is OK!!If you can find replacement of HSSR8400 it will be appreciated.It was much faster repair than I expected, now it will be little bit tricky to find connector replacement.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 02, 2016, 02:16:20 am
content: That's great. My repair was also quick and it took longer to track a replacement.I ended up using this parthttp://www.digikey.com/product-search/en?keywords=LH1510AAB-ND

author: plesa
author_rank: Frequent Contributor
timestamp: January 02, 2016, 12:27:06 pm
content: Thanks!!

author: HighVoltage
author_rank: Super Contributor
timestamp: January 02, 2016, 01:16:03 pm
content: First time I see the inside of a 34420A.Congratulations on the fast repair.I am looking forward to some measurements you will perform.Now you need a real SPRT sensor, like this one, to have one of the greatest thermometer.https://youtu.be/zQ5_oJI1cJM

author: plesa
author_rank: Frequent Contributor
timestamp: January 04, 2016, 08:20:36 pm
content: Quote from: HighVoltage on January 02, 2016, 01:16:03 pmI was quite surprised that they are using 25 Ohm.But back to the repair.In service notes I found that there are lot of issues related to older version of firmware and communication.http://servicenotes.literature.keysight.com/litapp/SearchSN.do?method=openExternalSNSearch&prodNum=34420A- RS-232 communication can be solved by replacing U700 ( Intel N83C51FA with 34401 marking )chip, fortunately my unit is OK, otherwise it will require return to Keysight. Chip is in socket so I do not know why. Maybe that's why there is attached sticker on instrument.BTW the version of this chip is the middle number in revision menu.- Firmware is stored in U502 (27C020 in PLCC32, Keysight blank can be ordered 1818-5187) in my unit is version 3.0 (first number in revision menu).Chip is also stored in socket so I do not understand why unit needs to be returned to vendor. That's a big difference compare to 34401A where both chips are soldered to board, where I understand that it is not customer job.Please send me PM if you have more recent version of firmware ( >4.0).

author: plesa
author_rank: Frequent Contributor
timestamp: January 07, 2016, 09:18:40 pm
content: After replacing obsolete HP HSSR8400 by Vishay LH1510AAB channel 1 is working properly.What I found as a new issue for solving is permanent overload on lowest 1mV range on both channels.I make low thermal short and check it on 10mV range, readout is below spec. 120nV on 10mV range and on 1mV is still overloadSo it must be connected to low voltage amplifier and to 10000 gain setting only.Gain in this range is switched controlled by ASIC U101, resistor networks is OK.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 07, 2016, 11:05:44 pm
content: I first thing to check is if the amplifier is somehow oscillating (ouput of U306). The feedback path is quite long and thus many places thing can go wrong. Candidates for failure are U303C and U303D.p.s. Funny how they made a low amplifier with an LM358.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 08, 2016, 01:32:03 am
content: Sounds like my recently repaired K2182. It had a bad resistor network. A couple of the resistors were open and all the low ranges were in overload.Good luck. If you need a comparison measurement, let me know.

author: plesa
author_rank: Frequent Contributor
timestamp: January 08, 2016, 07:20:14 am
content: Thanks, analog switches U303, U304 (DG411,DG211) looks OK. Both resistor networks as well.So I will check oscillations.Is anybody interested in posting old firmware?

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 08, 2016, 11:28:19 am
content: I will check my versions and upload what I have to xdevs. It won't be until later today.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 09, 2016, 01:26:40 am
content: Bad news, my rev 5 eprom is soldered to the pcb. It looks like it may have been replaced at one time. Another one has rev 6. I will open it later as I was gathering data for the Fluke 8808A thread.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 09, 2016, 03:32:16 am
content: Second 34420A with Rev 6 eprom is also soldered to main board.

author: plesa
author_rank: Frequent Contributor
timestamp: January 10, 2016, 05:05:11 pm
content: Thanks for check. It was similar on 34401A that some units has socket and some directly soldered EEPROM to PCB. Version 6 of firmware seems to be the most recent one. I will run lon term GPIB test and we will see if there will be some GPIB communication issues related to older firmware.When I inspected units I found that someone tried to fix channel 1 issue and desoldered Q128/Q129 FETs, I correct it and clean PCB. And I removed wire connections U313 pin 2 and C451 bypass cap, which looks like from unsuccessful repair.But it was mistake after putting the wire back the overload on 1mV range disappeared.Another issue what I found was on channel 1 and 10V range on autorange, sometimes the readout was 20-50mV.After replacing U120 HSSR8400 optocoupler by Vishay LH1510AAB everything works like charm.To prevent other issue I replaced all opto-couplers, but two additional without further improvement.On 2W ohm measurement seems to be offset 0.1 Ohm, but this I hope will be removed during calibration (still in spec) . 4W Ohm works ok ( 20uOhm stable readout, spec is 17uOhm).Quite good results for unit which was calibrated 20 years agoWith inputs shorted there is 48.5 uV on Channel 1 and 82uV on Channel 2 readout, which is according to spec OK.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 10, 2016, 06:01:47 pm
content: This is good news. After a long burn-in, we can collect some data on your 34420A. I can also do the same on mine as my 3458A testing has collected enough data to show how they are drifting. 3 of 4 tested fine. The last one is almost as bad as TiN's high plains drifter.

author: plesa
author_rank: Frequent Contributor
timestamp: January 10, 2016, 07:46:26 pm
content: I just assembled unit and overnight I would like to take first data set.

author: plesa
author_rank: Frequent Contributor
timestamp: January 17, 2016, 09:38:15 am
content: Data collected by BenchVue. Channel 1 noise 13.1nV, offset -8.5nV, Channel 2 noise 8nV, offset 28nV.Also I receive confirmation from Lemo about connectors:For cable FVN.1S.304.CLYC37Z price 50 EURmeter input connector is EVP.1S.304.CLY price 40EURboth with copper contacts not gold plated.EZGPIB scpit for some reasons seems to not work with my unit,old firmware issue maybe.

author: HighVoltage
author_rank: Super Contributor
timestamp: January 17, 2016, 10:57:36 am
content: Did the 2W Ohm reading correct the offset after calibration?

author: plesa
author_rank: Frequent Contributor
timestamp: January 17, 2016, 11:33:21 am
content: Quote from: HighVoltage on January 17, 2016, 10:57:36 amYes, all offset corrected after performing Zero calibration. Now the offset in 2W Ohm measurement is 125 uOhm!!Also the offset in DCV were corrected to -3nV on both channels. Currently I'm working on LabView program for data collection.I must say that I'm impressed by this meter.

author: alanambrose
author_rank: Frequent Contributor
timestamp: March 16, 2016, 05:58:42 pm
content: Re noise results - this seems to be the spec (rms at 10nplc / low impedance source):That is, lowest ppm noise on 10V range. 2-3x on other ranges except 1mV which is ~30x higher.And here are my early results - with a dodgy short as I don't have any proper connectors yet:Interestingly, lowest on 100mV range, with other ranges <1.8x that. The 1mV range seems good. My 1V and 10V ranges look out of spec, curiously.

author: alanambrose
author_rank: Frequent Contributor
timestamp: March 17, 2016, 01:00:10 pm
content: BTW anyone have an actual 34103A short that they don't mind taking the case off? I'm reluctant to pay $100 extra to have someone solder a couple of copper links into a FVN.1S.304.CLYC37Z Lemo. I was expecting this to be a crimp connection, but it looks like 'solder bucket' to me.TIA, Alan

author: Vgkid
author_rank: Super Contributor
timestamp: March 17, 2016, 02:04:16 pm
content: I believe in the Keithley info sheets, it says that they are soldered. I believe it was SN95AG5 solder, apparently what they seitched to after cadmium.

author: alanambrose
author_rank: Frequent Contributor
timestamp: March 17, 2016, 03:36:42 pm
content: Ah yes thanks...Model 2188 Low-Thermal CalibrationShorting Plug: A low-resistance, low-thermalshorting plug required to calibrate the Model2182A Nanovoltmeter. Made of a LEMO connectorwith its pin connectors shorted togetherusing copper wire and Sn/Ag4 silver solder.p.s. for the Europeans, the best place I've found for 96/4 is:http://www.reichelt.com/Solder/2/index.html?&ACTION=2&LA=2&OFFSET=500&GROUPID=557&SORT=artnr&SHOW=1i.e. the Felder Sn96 Ag4 F-SW32

author: alanambrose
author_rank: Frequent Contributor
timestamp: March 17, 2016, 05:17:23 pm
content: OK my first cut of the noise floor. My meter reporting firmware versions: 9.0-5.0-2.0 btw.(edit) Added the correct analysis.

author: plesa
author_rank: Frequent Contributor
timestamp: March 17, 2016, 05:30:31 pm
content: Quote from: alanambrose on March 17, 2016, 01:00:10 pmOf course. It is soldered. I cannot check the solder used, maybe later. For investigation I have also the input connector which is also soldered.

author: alanambrose
author_rank: Frequent Contributor
timestamp: March 17, 2016, 10:53:38 pm
content: Ah thanks so much - all the contacts are joined rather than just the two pairs?(edit) Duh, of course, for 4W ohms...

author: Goff
author_rank: Newbie
timestamp: April 20, 2019, 12:52:41 am
content: Hello,I'm new to the forum here andalready have a difficult question.Recently bought a "new" 34420A directly from Keysight Germany.Question: The meter has an inherent noise,it buzzes (not loud but not quiet),can anybody confirm this?Here are a few dates:Keysight 34420A- Green Display, white Keysight Logo- Date of first Calibration: Jul 2016 in Malaysia- Revision 10.0 - 5.0 - 3.0Thanks in advance for any answer!with friendly greetings from Germany,Goff

author: HighVoltage
author_rank: Super Contributor
timestamp: April 24, 2019, 08:21:19 am
content: Hello Goff and welcome to the Forum.The 34420A should not make any noise. The instrument does not have any fan (like the 34401A) and the noise that you describe might be resulting from a noisy transformer.I would contact Keysight in Böblingen and I am sure they will exchange to instrument to your total satisfaction.

author: plesa
author_rank: Frequent Contributor
timestamp: April 24, 2019, 07:03:58 pm
content: My meter is silent.Does not matter if new one or 20 years old one.Maybe the transformer shielding is not properly fixed.

author: Goff
author_rank: Newbie
timestamp: April 24, 2019, 07:56:01 pm
content: Hello plesa,thanks for the information / answer.... HighVoltage - Yes, the complaint was made.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: February 21, 2020, 08:22:30 am
content: Good afternoon.Is there a description of the change history of firmware 34420a?Has anyone seen on the network firmware files newer than 5-5-2?Are there any instructions and successful experience updating the firmware?I would be grateful for any information.

author: HighVoltage
author_rank: Super Contributor
timestamp: February 23, 2020, 01:38:52 pm
content: My two 34420A have following revision numbers:AgilentSN: MY42004xxxREV: 10.0-5.0-2.0KeysightSN: SG42000xxxREV: 10.0-5.0-3.0I would have expected a unit with higher SN to have a newer FW Revision.However, I do not see any differences in the functionality of the two instruments.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: February 23, 2020, 03:39:34 pm
content: Quote from: HighVoltage on February 23, 2020, 01:38:52 pmI met mention of a maximum belief of 10-5-5.Do you have the opportunity to read the contents of the flash?

author: branadic
author_rank: Super Contributor
timestamp: April 13, 2022, 06:03:55 am
content: Sorry to pick up that old thread, but has anyone ever created a firmware dump? I'm particulary interested in the firmware Rev3.0.-branadic-

author: branadic
author_rank: Super Contributor
timestamp: April 14, 2022, 08:03:27 am
content: I was sensitized to check my 10 V range with a battery powered LTZ reference to see if everything works as it's supposed to work. There was strange behavior reported by someone on a unit that was in for service. So I monitored the unit as suggested and the unit I have seems to do well. No excess noise, no strange jumping around, everything seems to be fine which indicates that my unit was a bargain.Edit: The test was performed at 10 NPLC and the filter turned off.Code:hp34420A.write("CONF:VOLT:DC 10;:SENS:VOLT:DC:NPLC 10;:INP:FILT:STAT OFF;") # 10V range, NPLC 10, Filter off-branadic-

author: HighVoltage
author_rank: Super Contributor
timestamp: April 14, 2022, 08:41:24 am
content: Looks nice!Now you need to do the same test on the other side of the spectrum in the nano volt rage with a stable 1 nV source.

author: alm
author_rank: Super Contributor
timestamp: April 14, 2022, 08:50:51 am
content: Quote from: HighVoltage on April 14, 2022, 08:41:24 amI think that's called a short

author: Kleinstein
author_rank: Super Contributor
timestamp: April 14, 2022, 09:49:20 am
content: The stability looks OK. Much of the lower frequency noise is likely from the LM399 reference in the 34420 and thus the popcorn type jumps of some 0.4 ppm.The 10 V range is a bit noisy, but that is a limitation of the ADC and there is not much that can be done there. This is not really a problem for the low ranges (1 mV and 10 mV), where this meter is good for.A test at the other end of the range would be either a short, or a 1 mV/ 10 mV source to be near the end of one of the lower ranges.The more interresting part would likely be the short and maybe some extra series resistance (e.g. 10 or 100 K) to see if there is drift / noise in the input current.

author: HighVoltage
author_rank: Super Contributor
timestamp: April 14, 2022, 02:12:48 pm
content: Quote from: alm on April 14, 2022, 08:50:51 amThe Keithley 260 Nano Volt Source is your friend for such measurements.Range: 0.01 nV to 1.11 VI can dial in 10 nV stable on my 34420A with the Keithley 260.Maybe we can call 0.01 nV a short.

author: TimFox
author_rank: Super Contributor
timestamp: April 14, 2022, 06:00:17 pm
content: The last voltage divider stage in that Keithley source is made of copper, despite its temperature co-efficient of resistance, in order to minimize thermal emf.

author: alm
author_rank: Super Contributor
timestamp: April 14, 2022, 09:41:36 pm
content: What's the noise like at 10 nV from the 260? The 34420a is specced for 1.3 nVrms, which I imagine is under absolutely ideal conditions re thermal gradients and cleanliness of connections.I actually had the Keithley 260 in the back of my mind when I wrote it, but I was in doubt even that can deliver a stable 1 nV outside a physics lab.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: April 15, 2022, 08:57:58 am
content: Since both resistors in the dividers are made of the same metal, their temperature coefficient is compensated.The noise level is determined by the output impedance. On the nV range, this is only 1 ohm. This is very little noise.

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 15, 2022, 09:15:20 am
content: Two years ago, I had a 34420A for repair on my bench.Using the same configuration and settings as branadics, w/o filter, it showed random excessive noise, triple the usual level, i.e. rms 7.6µV vs. 2.6µV.It had the same FW version 2.0.I measured stability of its reference, at the output of the input amplifier, with different GPIB adapters, and so on, and in the end could not identify the root cause. With branadics measurement, I now can rule out a FW error.The 2nd graph shows the calculated digital filter, like it would be implemented in the 34420A.Frank

author: HighVoltage
author_rank: Super Contributor
timestamp: April 15, 2022, 04:46:02 pm
content: Quote from: alm on April 14, 2022, 09:41:36 pmI don't remember and would have to measure this again.The Keithley 260 is well built inside for low EMF and low noise.Look at these impressive copper connections..

author: okti
author_rank: Contributor
timestamp: April 15, 2022, 08:15:12 pm
content: Here's my trusted old HP34420A at DCV10 NPLC10 FILTEROFF (source: LTZ1000) measurement fresh from the oven:

author: okti
author_rank: Contributor
timestamp: April 16, 2022, 09:11:42 am
content: Same meter, DC1mV NPLC10 FILTEROFF with short:

author: branadic
author_rank: Super Contributor
timestamp: April 16, 2022, 11:12:18 am
content: QuoteWould you mind explaining why you think that the ADC is the limiting factor here instead of the reference? To put some numbers to it, LM399 is typ. 7 µVrms, max. 50 µVrms noise (values for LM399, not LM199 in LT datasheet). Take that times ~1.4 for the +/-10 V reference voltage in the unit, which is the typ. 10µVrmsthat we are familiar with. The noise I see is smaller than that, indicating the noise of LM399 is smaller here.Has there been any report to the noise limit of a multislope III ADC, like feeding it with lower noise reference such as LTZ, that I've missed?-branadic-

author: Kleinstein
author_rank: Super Contributor
timestamp: April 16, 2022, 01:03:41 pm
content: The lower frequency noise (after the 50 points filtering) is to a large part the LM399 reference, though there could also be some 1/f noise from the resistors.The higher frequency noise seen for the single 10 PLC conversion looks quite high for a LM399 reference:I have looked at my test with an external LM399 reference and LM399 ref. at the ADC and there I get around 6 µV_peak to peak in between the popcorn events even with 1 PLC and some 12 µV peak to peak including the popcorn noise / longer time scales. 2 x LM399 reference at both ends would be comparabele to the 7 V scales up to 10 V. I have some reference filtering, but this would no longer be effective for 10 PLC and only 1 reference.The reportet noise for the 34401 that I found is somewhere around 2-2.5 µV RMS ( 12-15 µV peak to peak) for 10 PLC and I don't see much of the noise coming from the input stage, though there is a little. So this would explain much of the observed noise.I would be easy to measure that noise with a short.I have not seen much theoretical analysis on the 34401 type ADC noise, though I have just done some calculations on that. There are a few uncertainties, and my calculations still get a slightly lower noise ( some 1.4 µV RMS) from the noise sources I included. The noise is not just one large noise source, but more like a combination of many sources. From my analysis the worst offenders are the current noise of the OP27 in the integrator, higher frequency reference noise, jitter and quantization noise. In theory one could improve on the current noise and a little on jitter, but not with many other noise sources, especially not the quantization noise.There is one unknown in how the ADC is handling the first / last reference steps - that is the reference signal just before the auxiliary ADC is read. This part naturally will not be 100% effective and there is a chance that this factor is not perfectly treated in the firmware. This would be some extra discrete size errors, that can look rather random, though also changing with the input voltage. So some readings may be effected more than others.Ideally there would be a procedure in the factory calibration to minimize this error part, but I am not so sure they actually do this and if so, that factor may also change over time.

author: branadic
author_rank: Super Contributor
timestamp: April 16, 2022, 02:00:04 pm
content: I searched the web and found that report here: bbs.38hot.net/thread-69139-1-1.html where someone replaced the LM399 in 34401A by an LTZ1000 and noticed an improved noise behavior as well as improved t.c.. As 34420A is a somewhat pimped 34401A chances are that replacing it with a lower noise ADR1399 will slightly improve noise in 10 V range without to much hassle.-branadic-

author: Kleinstein
author_rank: Super Contributor
timestamp: April 16, 2022, 04:40:52 pm
content: The translated BBS38hot text is about a 34410, so a newer version with a completely different meter.As far as I see it the largest noise part in the ADC is the current noise of the OP27. This competes with the input signal though a 100 K resistor and calculated back to the input the noise would thus be current noise times 100 K. The 10 PLC AZ mode has an effective BW of 5 Hz because of the 2 conversions and an effective frequecy of 2.5 Hz for the 1/f noise. The datasheet gives a current noise for the OP27 of close to 1 pA/sqrt(Hz) at 20 Hz that would translate to some 3 pA at 2.5 Hz with a square root of frequency relation. However the DS says they measure the current noise with the resistor split over both inputs - which in my view is wrong: This suppresses the correlated part of the current noise and the uncorrelated current noise would only add as root. So at best the current noise figure is too small by a factor 1.4, and possibly more. So the current noise from the OP27 in the integrator would correspond to more than 3 pA/sqrt(Hz) *1.4*100 K = 420 nV/sqrt(Hz) of noise at the input. This would be 930 nV of RMS noise for the input (and possibly more from the correlated current noise part).The 2nd largest noise part would be the auxiliary ADC with it's quatization noise (around 350 nV/sqrt(Hz) for the input). Here it is a bit unclear how noisy the ADC is and especially in how much the contineous changing input may effect the µC internal ADC. So this noise part may be also quite a bit larger.The big unknown is how good the timing is when the auxilliary ADC is sampling: so does it get the last run-up step fully included or only partially and may need an extra correction factor for the last step.The 3rd largest noise I have in my list is the higher frequency ref. noise (could be some 150 nV/sqrt(Hz) for the input). The noise from jitter (likely mainly the 74HC4053) may reach a compable size.The ADC mixes back some reference noise from the 50-150 kHz band back the the near DC band. There is some parial filtering from the relatively slow AD706 OPs, but not full filtering. There is a good chance that some capacitance or better capacitance with series resistance (similar to the suggested ARD1399 circuit) in prallel to the LM399 reference could reduce the higher frequency noise. So something like 1 µF+5-10 Ohms in parallel to the 7 V from the LM399. There is a chance this would reduce the reference noise on the 100 kHz frequency band. It is not the largest noise source, but also a relatively small change.

author: bigboss59
author_rank: Contributor
timestamp: May 31, 2025, 05:06:18 pm
content: Quote from: plesa on March 17, 2016, 05:30:31 pmSorry to digBut my question is related to the picture hence it didn't have sense to open a new topicAnyway I don't clearly understand why the 2 inputs are connected together and also why only 3 bridges then ?

author: Kleinstein
author_rank: Super Contributor
timestamp: May 31, 2025, 06:44:29 pm
content: The short is likely made for the 4 wire ohms case. Links are enough to connect the 4 terminals. Ideally these should be in a sequence drive - drive - sense - sense and not with a drive between 2 sense or the other way around.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 01, 2025, 10:36:01 am
content: Many years ago, I bought the original short block and I also made one myself.The original short has bare copper connectorsThe self made short has gold plated connectors.I was surprised how bid the difference was.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 01, 2025, 10:41:38 am
content: Results:It seems the bare copper makes a bigger difference than the way of connecting the short.

author: bigboss59
author_rank: Contributor
timestamp: June 08, 2025, 11:38:43 am
content: Thanks for your reply guysIs there any revision history (like we can found on the HP34401A for instance) ?My version is 3.0-5.0-2.0, I guess I could upgrade it ? (supposing there are no HW changes) However I was unable to find versions online. Any guess ?Does the copper connections matter for no short measurements ?I know the copper connections is a specific part from LEMO, the cheapest way is to ask LEMO directly ?When I perform a short measurement with the home made cable I received with the (used) unitLemo (I suppose FFA.1S.304.CLAC52) gold connector, sn62pb36ag2, no copper spade connection, 1m CCL 7-2-4C 0.22mm² (copper covered with ?)I got 0 to 0.1uOhms (4W)I wasn't expecting such result maybe I was lucky to not pick up any interferences ? I do understand the point of short shortplug but seeing this kind of result makes me question it ?Thanks !

author: picburner
author_rank: Frequent Contributor
timestamp: June 08, 2025, 07:54:17 pm
content: The exact code of the LEMO connector is FVN.1S.304.CLYC37Z.As far as I know LEMO also sells directly but I think there is a minimum quantity for the order.I bought mine from Mouser.Attached are some firmware for the instrument up to REV 10.0

author: bigboss59
author_rank: Contributor
timestamp: June 09, 2025, 07:58:50 pm
content: Thanks a lot for the files !Is the FVN.1S.304.CLYC37Z connection made of copper ?Am I safe to go from 3 to 10 ?I can't find if there are any HW modifications between 3 to 10 ?Will the calibration mapping (which I believe is stored in another flash) be the same between rev 3 and 10 ? As I don't want to loose calibration during the update.

author: picburner
author_rank: Frequent Contributor
timestamp: June 10, 2025, 04:27:12 am
content: QuoteYesQuoteI don't know. I have rev 10.0 already.But to be safe you can make a backup of the 93C66 eeprom (U505).You don't even need to unsolder it, just keep the processor in reset state to read it (and if necessary, rewrite it).

author: bigboss59
author_rank: Contributor
timestamp: June 10, 2025, 10:33:01 am
content: Thanks for your replyI will try the update once I'm sure there is no HW changes between 3 and 10 revision otherwise I will not as I have no way of checking my deviceHopefully someone can confirm this ?