Agilent 34401a revisions - Page 1
Forum section: electronics / testgear

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: February 14, 2019, 04:40:35 am
content: Hey everyone,I have a couple questions regarding the 34401a that I cannot find any information on the web, I hope you can help:I understand the last and final firmware level is Rev 10, for those of you who has it installed in your DMM, what is the three revisions levels when you look it up in the System MenuI just ordered a new front display board from Keysight, it upgraded the last revision number (display) to 03 (I had 02 in my old panel). Does anyone know what are the changes between 02 and 03? Is it just a hardware revision? Or is there actually some real firmware changes?Thanks to all the wisdom shared by this wonderful community, the panel swapped out was a piece of cake.

author: coromonadalix
author_rank: Super Contributor
timestamp: February 14, 2019, 10:53:18 am
content: There is a revision 11, but you have to send it at Keysight, they wont sell you directly the firmware chip, i've tried ... and i dont know how much it cost ..For the revisions i did not see any paper /document about that, maybe ask Keysight for the changes ??Brief Historyon the 34401A-06 service noteUp to the fw 06-04-01 you will have the old unobtanium display chip, pcb: 34401-66502Past the fw 06-04-02 you'll get the newest more repairable display pcb pcb: 34401-66512You can still order the newest pcb version 34401-66512, but the quantity is low ... and the price is high, around 200$ in my country, dont know how much you've paid for it ?There is a version 10 leaked in the attachement, never tried it, it is supposed to work if you reprogram your (U502) fw chip and put the newest display pcb ... never heard of anyone doing itFor the VFD (vacuuum display) pn: 2090-0296 it is not orderable from Keysight anymore, you have to rely on chinesium parts around the web.Some have success, others dont, I have seen some Samsung and Itron named / printed on them ??I have ordered 2 vfd's to replace one dimmed at 50% in one of my meter, time will tell when i have them delivered.I hope they have protected the pins as i asked ..... they told me yes ...I will tell my source if it work ... around 30$ usd each ... not from Ebay.

author: HighVoltage
author_rank: Super Contributor
timestamp: February 14, 2019, 11:15:21 am
content: A few years ago, the VFD on ebay from far east were really good quality.Lately, like in the last 2 years, every single one I bought was not nearly as good as they used to be and I have given up on buying them from ebay.The VFD with the attached PCB is worth the money from Keysight, as long as we can get them.

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: February 14, 2019, 12:39:39 pm
content: Thanks for the info, I was able to order the front display board from Keysight in the US. It is $150 plus tax, but it saved me the headache of having to deal with the eBay vendors. I think it is well worth it as it keeps everything original.My meter now has revision 11-05-03 on it from what it is worth, would be interesting to see if there’s anything more current.It would be interesting to see if anyone knows what is different about the V3 display.Thank you for all the info you shared.

author: HighVoltage
author_rank: Super Contributor
timestamp: February 14, 2019, 02:57:16 pm
content: I have on of the last produced 34401A and it is made in Singapore in 2016/2017.It has11-05-03installed.It seems that 11-05-03 is installed in all Keysight branded models.But I have not noticed any thing different from older 34401A

author: coromonadalix
author_rank: Super Contributor
timestamp: February 14, 2019, 03:08:13 pm
content: Damn i want one badly loll

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: February 14, 2019, 05:40:11 pm
content: Thanks for sharing the version info, as it has been a mystery that I cannot find on the web anywhere. All I was able to find was the Agilent video from 2014. Back then the display was still at revision 2.I do enjoy using the unit, it is a reliable and responsive DMM.

author: mr.fabe
author_rank: Regular Contributor
timestamp: February 14, 2019, 10:54:00 pm
content: I have an Agilent branded 34401a assembled in Malaysia with the 11-05-02 FW.Sent from my Moto Z (2) using Tapatalk

author: JohnPi
author_rank: Regular Contributor
timestamp: April 10, 2020, 05:33:56 am
content: I have a newer one that is 11-5-2, and older ones that are 10-5-2. All are labelled 'Agilent'.I'm puzzling over some SCPI commands, but so far the only difference I see is that the '11' one lights the 'Adrs' annunciated while in remote. I'm not sure why.

author: Peter_O
author_rank: Frequent Contributor
timestamp: April 27, 2021, 02:33:28 pm
content: I've just fetched a 11-05-02. Display not brilliant but OK.I wonder which manual to download and print.Would the 2014 Edition 10 User's Guide from the keysight website be OK, or do I need to look for a special one?

author: jusaca
author_rank: Unknown
timestamp: April 29, 2021, 04:13:07 pm
content: Quote from: Peter_O on April 27, 2021, 02:33:28 pmI would say that is wasted paper and ink. I played around with my one for an hour and got almost everything working. Then I skimmed through the manual to understand the last tricks and details.Regarding which manual to use - I think it does not really matter at all. As far as I can tell, they did not change anything regarding the way to use the meter.

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: May 03, 2021, 04:22:14 am
content: I think that version is fine. By 2014, it is running on the final 11-5-3 firmware. I have two units, one with 11-5-3, the other with 11-5-2. The last digit is the display board firmware, I have not been able to detect any operational difference between them.I also agree with jusaca on the printed manual, I have both set of the original manuals that came with the meter still in shrink wrap, and I have never opened them. I only use the PDF version, much easier to search. If you are going to go through the effort to print them, you might as well just purchase the real hard copy.

author: Neo2199
author_rank: Contributor
timestamp: January 11, 2022, 06:39:52 pm
content: Hi, sorry to revive this old thread, but I just got my 34401A and by checking revision it says REV 01-01-01. Does anyone know what it means? Should I attempt to update?

author: dorkshoei
author_rank: Frequent Contributor
timestamp: January 11, 2022, 06:46:11 pm
content: Quote from: Neo2199 on January 11, 2022, 06:39:52 pmmeasurement processor revision -- i/o processor revision -- front panel processor revision01-01-01 seems suspicious to me. Did you obtain it from the procedure shown here?What is the serial# and county of manufacturer (on rear)?Upgrading is not as simple as flashing new firmware.

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: January 12, 2022, 12:06:57 am
content: Wow, that would be the original edition at launch. I have never seen a unit in that firmware level either.I have never been able to get any detail on the changelog, upgrading firmware requires you to program a new U502 ROM, and I believe it will also require a recalibration. So unless you have a reason to upgrade, it may not be worth the effort. Due to the age of the meter, perhaps a full functional test and accuracy check should come first.Good luck.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: January 12, 2022, 12:14:32 am
content: There are hardware barriers that limit how far one can upgrade each component. Service guide has some into but its not complete as,its a static doc. Keysight may have more info. Also some upgrades even if hw supportsl can only be done by keysight.Without confirmation of a very early serial i suspect version reported is not correct

author: Neo2199
author_rank: Contributor
timestamp: January 13, 2022, 01:04:30 am
content: Yes, I have followed up the video.the SN:3146A01412 Made in U.S.A.Yeah I know the upgrade will be hard, just wondering if it is worth it. The only reasonable version would be 05-01-01. The others require different display board. Also bit worried about difference in the main board HW in respect to firmware.By the way, looks like xDevs repaired the same version of 34401Ahttps://xdevs.com/fix/hp34401a/Yeah, my current plan is to replace all tantalum and electrolytic caps, get missing fuse holder then full accuracy and functionality check, then will see.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 13, 2022, 03:02:18 am
content: wow thats a firstBut you have the unobtanium display circuit, you can not put any type of firmware in itAnd you can not put the more modern display in replacement of the unobtanium one, if you dont flash the main eeprom unit, there is a note i've read on the manualspretty darn clean meter, looks like a time machine lollAnd yes the accuracy should be checked first, if it aint broke dont touch itThe revision 11 of the display firmware was in the past only obtainable from keysight if you did an meter exchange, dont know if that condition changed ??And their exchange system is pricey as $$$I would be curious to see their reaction when you told them that you have the first version ... and you want to get the firmwares changes / history if there is one to getDigikey has the two different fuse sockets and the fuse caps, beware they are separated parts not a kit, i managed to get theses parts to rebuild one of my 34401aEven the main ac socket can be found, not on the keysight parts page, was around 40$ few years agoI recapped my meters and worked them with an hot air desoldering station and used kapton tape to protect the surrounding parts from over heating, and do use anti static gloves and proper groundingOnce recapped, they where sent for calibration and passed with flying colors, and one of them received clone VFD from AliExpress at 30$ usd at the time

author: Zoli
author_rank: Frequent Contributor
timestamp: January 13, 2022, 04:45:35 am
content: Quote from: Neo2199 on January 13, 2022, 01:04:30 amThe fuse holder is Schurter 0031.3558(digikey 0 stock); maybe is cheaper/simpler to order from online distributors then from Keysight, considering the late habits.

author: Neo2199
author_rank: Contributor
timestamp: January 13, 2022, 05:51:59 am
content: Thanks for all the advice. All good info.I will probably stick with if it ain't broke, don't touch it. We will see how the performance testing goes.I actually got the fuse from Mouser.https://www.mouser.com/ProductDetail/693-0031.3558have last 4 in stock...

author: dorkshoei
author_rank: Frequent Contributor
timestamp: January 13, 2022, 06:07:59 am
content: Quote from: Zoli on January 13, 2022, 04:45:35 amAre you sure? I thought it was 0031.3551. 0031.3558 uses the same inner fuse holder and that can be removed and used on the 34401.3558 was in stock yesterday but gone today :-(Quote from: Neo2199 on January 13, 2022, 05:51:59 amThat would be my advise.

author: Zoli
author_rank: Frequent Contributor
timestamp: January 13, 2022, 06:18:02 am
content: Quote from: dorkshoei on January 13, 2022, 06:07:59 amI can confirm that the removable part is identical, since I've changed it on my HP(worn out slot, otherwise functional; I think that multimeter eated up more then 100 fuses....); I cannot speak for the PCB part, because I didn't changed it.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: January 13, 2022, 06:28:38 am
content: Quote from: Zoli on January 13, 2022, 06:18:02 amI know. I was just saying that 0031.3551 is the actual pcb part and removable part. If you just need the removable holder (which most people do) 3558 is fine and you can discard the pcb part.

author: Neo2199
author_rank: Contributor
timestamp: January 14, 2022, 04:32:18 am
content: Yes, just the removable part. Should be fine. THX

author: NaxFM
author_rank: Regular Contributor
timestamp: January 14, 2022, 08:13:23 pm
content: I just bought a 34401a made in the USA with the red connectors, It is marked agilent but has the HP symbol on the serial number sticker. However the serial number is the new format (US12345...)Let's just hope it has the new revision, i'll let you know the serial number and the firmware version when i recieve it.According to another user on another post, it should have the newer pcb, we'll see...However, there's something i didn't quite understood. The firmware version is just an academic excercise to determine when it was manufactured, right? Does the firmware matters aside from understanding if it uses the new display board?

author: dorkshoei
author_rank: Frequent Contributor
timestamp: January 14, 2022, 09:12:28 pm
content: Quote from: NaxFM on January 14, 2022, 08:13:23 pmWrong.QuoteRead thru the service notes. For example note 34401A-04 describes a (the?) difference between 01-01-01 and 02-01-01 firmware.Serial Numbers: 3146A00100 / 3146A03335 (Firmware Revision 1 – REV 01-01-01)Explanation of indicated calibration failure of AC currentStarting with Revision 2 firmware (REV 02-01-01) a calibration was added at the 10 mAlevel on the 1 AAC current range. Units prior to this revision will meet specifications butare not designed to accept a calibration at this point. However, using the STE9000 testsoftware (Application Part #5011-1013) they will indicate “fail” for this adjustment on theSCAT II “adjustment report” if the AC current calibration is attempted.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: January 14, 2022, 09:17:33 pm
content: Also look at the "backdating" section of the 34401A service manual.In reference to the above 01-01-01 -> 02-01-01 change you will see:From 3146A03335 and Below Modify A1U502 34401-8881 Programmed EPROM

author: NaxFM
author_rank: Regular Contributor
timestamp: January 19, 2022, 12:58:51 pm
content: Just got my first 34401A!It's made in the USA and it still has the HP branding on the back, the serial number is US36074928 and the firmware version is 10-05-02, so the most recent Agilent one.Honesly I didn't expect such an updated firmware, the unit seems quite old...

author: dorkshoei
author_rank: Frequent Contributor
timestamp: January 19, 2022, 02:49:12 pm
content: They are old :-) I think Keysight made a 03 display board but other than this they didn't make that many changes before it was discontinued.You can get the bumper and handles from China for cheap.https://www.ebay.com/itm/184419854408That's the new handle design. You can get both but be sure to specify. I can't recall if your unit had the old or new. Maybe the new style was just for the oval blue button. Someone will know, or it doesn't matter.

author: HighVoltage
author_rank: Super Contributor
timestamp: January 19, 2022, 02:52:17 pm
content: Quote from: NaxFM on January 19, 2022, 12:58:51 pmNice, congratulations.Someone exchanged the window already from a HP brand to Agilent brand, that is also nice.Yes, I agree, get some bumpers and a handle and it will look even better !

author: gerryc89
author_rank: Contributor
timestamp: February 15, 2023, 02:52:44 am
content: Hi to all, i recentrly obtained two multimeters in bad condition, with different board revision, one with v05 and one with v11. I Have repaired all of these, with this occasion i have analyzed the differences between two models and i have extracted also the two firmware of the comm cpu v1 and v5. In the beckdating section of the service manual i have verified the difference and the result is this:first change board revisionC111 100 pF ±5% 50 V addC402 220 pF ±5% 50 V addR327 21.5K ±1% .125W addR403 8.25K ±1% .125W replace 12.1kR422 46.4 ±1% .125W addR430 Zero Ohm replace 14.7ohmU102 custom resistor, i think is only a different production, i have measured the two different codes without desoldering and is very closestsecond change only componentsCR203 Zener 5.1V 5% replace 4.7vR207 2.37K ±1% .125W replace 5.62k in manual, but mine is 1.78k, other in photos are 1kother changes is only production variation, the last important change is the dipslay panel from version 07 and the firmwares of main and comm cpui have analyzed the differences and i have founded this:The gate of mosfet q301 is connecet thrugh the r327 resistor, i think it work only in saturation and the resistor decraese the stress on the switch ic.The power to U411 and relative cap C410 is delivered by u401 5v reference buffer thrugh the r422 resistor, instead from u553Replaced the zener voltage that power the ohm current generator from 4.7v to 5.1vThe pin vee of the mux U411 is connected to gnd only with the inductor, insted the r430 in seriesOther changes in the amplifiers chain of the final stages that go in the adc.Someone think that all this changes can be do on the old pcb for update all hardware without concequences? Improve something? Obvius that a recalibration is necessary.Here is the firmware of comm cpu u700 that i have dumpedhttp://www.ko4bb.com/getsimple/index.php?id=manuals&dir=HP_Agilent/HP_34401A_6.5_Digit_MultimeterIn the latest revision of the pcb is present a jumper that connect to ground the a4 address line of the ram, if the jumper is removed the gnd disappear from signal and remain connected to the cpu pin 27 that is an high speed output, on the old revision this pin is grounded and the a4 line of the ram is connected to vcc, the result is the same, a part of the ram is unused. Is interesting if on the firmware effectively is supported.regardsgerry

author: gerryc89
author_rank: Contributor
timestamp: February 15, 2023, 02:58:04 am
content: other images

author: Kleinstein
author_rank: Super Contributor
timestamp: February 15, 2023, 08:30:30 am
content: Quote from: gerryc89 on February 15, 2023, 02:52:44 amThe old HW was working OK and it is not clear if the changes really improve things. Some of them could be because of minor changes to the custom chips (e.g. c111 may have been inside on older hybrid version, or just needed because of other changes inside).I don't see any reason to change things - the changes don't look like they would fix a serious bug.

author: gerryc89
author_rank: Contributor
timestamp: February 15, 2023, 12:22:38 pm
content: Quote from: Kleinstein on February 15, 2023, 08:30:30 amI have the same opinion, but is interesting if enchange a crosstalk noise on the adc switch U411, the current of the ohm gen i think is the same only change the open voltage.You have some ideas regard the last opamp stage of the comparator input for the asic? The asic is the same, only change the custom resistor array but the ohm values seems to be the same.Gerry

author: Kleinstein
author_rank: Super Contributor
timestamp: February 15, 2023, 01:57:30 pm
content: The comparator input to the asci would effect how well the integrator tracks zero. So a change here can effect how large the excursion of the intergrator can be.For some reason HP claims that this would help with the INL due to dielectric absorbtion, as there is less average voltage in the intergrator. However as far as I see it, the extra small contribution via R406 adds a linear part and thus mainly a small effect on the ADC gain, but hardly the linearity. With the rather fast modulation there is anyway not much INL effect due to dielectric absorption expected, unless the integration capacitor is a high DA type.The part still makes sense, as less maximum voltage also means that a smaller integration capacitor can be used and for the MS3 ADC the auxiliary ADCs sees a smaller voltage range. So The R403 / R406 part can improve the resolution, which is one of the weaker points of the MS3-adc.I don't know why the value or R403 changed. It could be a BOM simplification or from looking at the worst case instead of average integrator output voltage. The ideal value for the R403/R406 part also depends on things like the delay of the comparator and the size of the integration capacitor (may include tolerances). The change may be just to allow for more scattering in the capacitors (lower reject rate from capacitors on the small side).Using U411 to also supply the HC4053 switch is a balance: the supply of the 4053 has some small, but visible effect on the ADC ( My ADC design is similar in using a 4053 type switch).Using the voltage from U411 makes the supply more stable (U553 can show quite some temperature effect). With the ADC constantly running I would not expect that much variations in the supply current of the HC4053. So the crosstalk back to the 5 V ref may not be that bad. The change likely improves the ADC a little and adds a little noise to the ohm- part current sources and input amplifier.The 100 nF decoupling capacitor seems to be sufficient. I don't understand the odd 46 Ohm value. If critical they could have used more decoupling.

author: gerryc89
author_rank: Contributor
timestamp: February 16, 2023, 08:15:12 pm
content: Other two dmm back to life, full recap and i have also upgraded the main eprom and comm cpu. I have utilized a 2Mbit flash with bootblock, it work because the reset pin is already connected to vcc(plan to install another otp and remove the socket for evitate possible data corruptions because the write pin is connected to the cpu), i have also adapted the calibration eeprom inserting from the v11 cal the 0x14-0x4F zone to address 0x14 of the original, rewrite the zone 0x0c-0x13 with v11 data, and cut the file to 0x1FF, it work for v2 to v6 i think. The display v1 appear to work on v11 but i have scanned the pcb for reproduction of the v2 panel. No error messages for calibration, i have partially tested and appear to work correctly, i have to try the loopback of the rs232 and gpib but the software seems to start and run correctly on the 87C51FA from NXP. I have also exchanged the red black rear connectors of the new version to the front of the old.Gerry

author: Miti
author_rank: Super Contributor
timestamp: February 18, 2023, 12:03:21 pm
content: Quote from: gerryc89 on February 16, 2023, 08:15:12 pmWhy did you have to upgrade the comm cpu? Is there any writing about this?Cheers,Miti

author: gerryc89
author_rank: Contributor
timestamp: February 18, 2023, 04:21:35 pm
content: Quote from: Miti on February 18, 2023, 12:03:21 pmI have upgraded for evitate compatibilty problems, i don't know if is effectively necessary, and for try to extract the firmware from the controller that isn't avaiable online until now. In the change history the u502 and u700 are changed together more of two times. For programming the 87c51fa the tl866 or tl866ii work very well, only the tl866II have a bug in the software that if you close the xgpro application the chip can't be verified anymore, but is a problem to verify the encryption array, it program the chip correctly, i have signaled the bug to xgecu. The rs232 comunication work ok after update.Gerry

author: gerryc89
author_rank: Contributor
timestamp: February 27, 2023, 11:08:00 pm
content: I have recreated the layout of the v2 front panel and populated it with all components. The mcu is an AT89C51, it is the eeprom version of otp 87C51. It work very well and fit exactly like the original, the spare code of only the pcb is 34401-26512 , assembled with components is 34401-66512. I have others 9 pcb's if somewone is interested, are gold plated with mask, the only thing that is difficult to get is the resonator, the only that i have found is too little and i have mountend upside-down with wires.Gerry

author: coromonadalix
author_rank: Super Contributor
timestamp: February 28, 2023, 02:25:42 am
content: Woah you really did a new front pcbkudos

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: February 28, 2023, 06:11:10 am
content: Excellent work on the PCB. I was able to order a replacement front board through Keysight a couple years ago to replace my dimmed VFD, but the part is no longer orderable now, so your work will really help out those who needs front board repair beyond the VFD.

author: gerryc89
author_rank: Contributor
timestamp: February 28, 2023, 10:35:29 pm
content: Thanks to all the informations on the forum for the calibration EEPROM and checksum i can do It, this Is my little contribuireI think that is possibile to create, without much effort, a led version with the same CPU and some shift registrers led drivers. Kingbright make a type of 14 segments and dot in smd format that Is to little to integrate in the panel.Gerry

author: Hydron
author_rank: Super Contributor
timestamp: March 01, 2023, 01:16:17 pm
content: Is there a reliable source for the VFDs (by themselves) at the moment? I've seen some comments about the aliexpress/ebay ones being a bit hit and miss, and my 34401A VFD is usable but a bit tired, so it would be nice to replace it if there is a source of good new ones. That replacement board is tempting though - would let you build a new display without risking breaking a dim-but-working one in the process!

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: March 01, 2023, 03:19:56 pm
content: I have seen the same feedback from replacement VFD, lots of hits and misses, depending on the marketplace sellers, and even from the same seller. I have also seen some where the product does not match the description, or the pictures posted, and I hate to wait to get something from China, find out it doesn't work and try to get an refund or replacement. But still, that's the cheapest route, I just never went down that path. Switching out the VFD is not that hard, I have done a couple with donor units with original parts, a desoldering gun would help greatly, so the risk for ruining the PCB is low as long as there is a good match in the replacement parts with the original (which can cause trouble with the metal shroud with shorting pins out).Back then, I was able to work with someone I know at keysight to obtain a parts authorization for order, so I was able to place an order through sales for the entire PCA front panel for $149. But currently, the only way to get the parts is through their repair service, so that option is no longer available.For measurement that requires high accuracy, I tend to leave my DMM on. On my 34401As, I now would leave the display off until I need to do a series of measurements to avoid any VFD aging issues, this is one practice I would suggest for other 34401A owners. It is a bit of a hassle, but not too bad once it becomes part of your workflow.I think all these made the work from gerryc89 so much more important, so we can keep our 34401A in service. I love it because it is fanless and very stable long term, I am not sure if there are other 6.5 digit meter that can do this. I would love to see what he or others would do with alternate display technologies.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 01, 2023, 05:48:36 pm
content: As we wrote on other threads Keysight where about to statuate a no longer available front pcb with the original vfd soldered on itit was about 195$ usd at the time, 2 years ago, good luck if you find onei bought 2x clone vfd on Aliexpress when they came out 35$ usd each, had no problems with them, maybe i was luckyBough recently a clone for the 34410a version, no problems, but a very tight fit, have to be very careful, the bent pins are done too far away from the vfd glass, works very well 200$ CAD deliveredAnd finally you have an oled made display version here from Qu1ck, i helped him with probing signals from a more recent model .... Fw 10-x-xand yes some meters have a display off command sent thru gpib too

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: March 01, 2023, 06:48:37 pm
content: Yes, you can turn the display off via GPIB, but I typically do not want to power up my PC just to do that, so I just do it via the front panel. Both my 34401A are later built with firmware 11, are you saying some earlier firmware does not have the ability to turn off the display through the front panel?I will have to look up the OLED upgrade, is OLED burn-in an issue? That's why the LED option sound appealing, but clearly the items other than digits would be a problem to replicate without something like an OLED.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 01, 2023, 07:50:38 pm
content: yes oleds have some issuesthere is a project here too have an external character lcd connected to a 34401a, maybe with some code fiddling you can adapt it to your needsor the qu1ck oled project could be adapted in a way with an bigger graphical / characters lcd too ?? since the protocol decoding was shared .... the fun is yoursor unless you want to take thehttps://www.eevblog.com/forum/buysellwanted/ebay-led-display-module-fluke-8840a42a-(diy-kit)-replace-broken-damaged-vfd/But i dont think you have enough supply power in the 34401a, i would not advice to take power from any source inside it ...or finally whack you own controller sending vfd shut down commands on the gpib connector loll

author: gerryc89
author_rank: Contributor
timestamp: March 02, 2023, 10:04:46 am
content: One power supply that have a great current capacity Is present, Is the filament secondary, if the central winding of the trafo Is disconnected (Blue wire, that create the chatode referente voltage with a zener), It can be full wave rectified and used to power some led displays without touch balanced 18v rails, or only for the mcu.Gerry

author: coromonadalix
author_rank: Super Contributor
timestamp: March 02, 2023, 10:57:14 am
content: yeah could try that filament supply, but you have other supply for digital and analog sections, if you touch them you could create instabilitiesyou have enough place to add an small psu on the ac main line and feed a substitue display mcu etc ....

author: alan.bain
author_rank: Regular Contributor
timestamp: March 02, 2023, 11:43:33 am
content: On the 01-01-01 version it is worth noting that the command to query the firmware version on the 34401 constructs it from two RAM locations (on the 7-5-2 firmware there are 0x1708 for the release (-2) and 0x1A3E for the minor version (location is 50, /10=>5). So there are ways in which this could go wrong! Only the first digit major version (7) is a direct read from ROM.And of course the SYST:VERS? command gives the SCPI set supported (this is from ROM) so on 7-5-2 this is 1991.0

author: Miti
author_rank: Super Contributor
timestamp: April 23, 2023, 01:40:55 am
content: Quote from: Hydron on March 01, 2023, 01:16:17 pmI just replaced mine with this one from AliExpress:https://a.aliexpress.com/_mN8vcfIIt’s not exactly what is shown in the picture, it doesn’t say Samsung anywhere, but it works well and the price is reasonable, 53.62 CAD including shipping.Attached are the pictures before and after.Cheers,Miti

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: April 23, 2023, 05:28:15 am
content: Looks great, best price I have seen yet.

author: Hydron
author_rank: Super Contributor
timestamp: April 23, 2023, 08:27:22 am
content: Yeah thanks for the tip Miti, I assume it appeared brand new as claimed? Results suggest so!

author: charlyd
author_rank: Frequent Contributor
timestamp: April 23, 2023, 12:00:39 pm
content: did somebody export V11 from the chip already to a file? as Agilent/Keysight is not distributing as coromonadalix stated in his post #1maybe post more FW updates if worthless, for different generations i saw v10 already. ( i did investigate it yet but isn t is a matter of a programmer? )

author: Hydron
author_rank: Super Contributor
timestamp: April 23, 2023, 12:21:44 pm
content: IIRC v11 is available on xdevs

author: Miti
author_rank: Super Contributor
timestamp: April 23, 2023, 02:17:35 pm
content: Quote from: Hydron on April 23, 2023, 08:27:22 amYes, it does look brand new but the pins are tinned a bit sloppy. I assume the pins are made of a material that is not easy solderable, that's why they have a method to tin them and that's why it looks like it was soldered before but as you said, the results suggest brand new. We'll see how long it lasts. I kept the old one, just in case.Miti

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: April 23, 2023, 02:32:09 pm
content: All the ones I saw are new, but of varying quality. Keep us posted on how it holds up, my guess is they will be fine unless you leave the display and equipment on continuously.I also notice the color has more yellow in it, but the fact it fits well and evenly lit is what really matters.$28.79 delivered to the US, I am ordering one as I may need one for my two 34401A some day.

author: Hydron
author_rank: Super Contributor
timestamp: April 23, 2023, 04:10:11 pm
content: Thanks Miti, just placed my own order for one, will also keep my (usable but a bit tired) old one as a backup.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: April 23, 2023, 04:29:36 pm
content: I bought two of the new "Samsung" marked ones off aliE. I doubt they are made by Samsung.Both were fine.Buy from the seller with the most #orders and then most #reviews of the specific product.They're all buying from wholesalers and so it's a lottery.

author: gerryc89
author_rank: Contributor
timestamp: April 23, 2023, 07:48:23 pm
content: Quote from: Miti on April 23, 2023, 02:17:35 pmIf you have difficult to solder on a metal that create problems of oxidation you can use the chloridric acid saturated with zinc, a little bit on the pins and the solderability increase immediatly,Gerry

author: Miti
author_rank: Super Contributor
timestamp: April 23, 2023, 10:31:25 pm
content: Quote from: NoisyBoy on April 23, 2023, 02:32:09 pmNope, it's my phone camera or probably different lighting. I compare it to another meter with genuine Itron VFD and I cannot see any difference in color, but the new one is brighter.

author: Swainster
author_rank: Frequent Contributor
timestamp: April 25, 2023, 02:39:59 am
content: Quote from: gerryc89 on April 23, 2023, 07:48:23 pmIn the UK, you can find this solution, or something similar, under the name "Bakers No 3 Soldering fluid". It's pretty strong stuff, so after tinning the leads, I'd make sure the new panel was very well washed/rinsed before bringing anywhere near the 34401A display PCB.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: April 25, 2023, 03:27:11 am
content: bought ver 03-01-01 , LM399 on socket, VFD almost dead, green screen missed, quite scratched, but all work ... should i solder LM ? ... I think so ...

author: razvan784
author_rank: Regular Contributor
timestamp: April 25, 2023, 08:05:29 am
content: The LM399 is socketed on all revisions. It is not a plain LM399 but it is aged and selected. I wouldn't touch it with a soldering iron, the heat might throw off the calibration and affect long-term stability.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 25, 2023, 11:37:17 am
content: MMM i would say on the 3 34401a meter i have / had, the lm399 where not socketed ... all of them have been openedthey where the series with all red input plugs .... but not having the unobtanium display driver rev 7 ......

author: razvan784
author_rank: Regular Contributor
timestamp: April 25, 2023, 12:09:25 pm
content: It's right there in the service manual parts list.U403 is the voltage reference.US403 is the socket, hp p/n 1200-1672, mfg p/n SBL-041-SP122-TG30.Please don't put a hot soldering iron near a precision reference!

author: Swainster
author_rank: Frequent Contributor
timestamp: April 25, 2023, 01:33:24 pm
content: I've got two of the later version (agilent branded), and both have socketed references. In fact, someone had nicked the reference out of one of them before they got to me. I've also have an earlier HP branded all red jack version. I've not had it open yet, as it's never shown a problem, but maybe I'll take a peak inside and report back.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: April 25, 2023, 11:39:34 pm
content: Quote from: razvan784 on April 25, 2023, 08:05:29 amand possibly exorcised Agilent soul that usually adjust temperature and Sebeck effectfrankly, in such current state of device, worried about Vref jump to a few microvolts.... naaai do adjustment when 6 digit running constantly at least 6-9 month. and that particular unit need a board clean up , it has some current leakage. when Gohm mode on

author: Miti
author_rank: Super Contributor
timestamp: April 26, 2023, 07:45:49 pm
content: I keep seeing Service Note 34401A-06 mentioned in various posts but I can’t find it anywhere. Do you have a link or can you attach it here?Cheers,Miti

author: coromonadalix
author_rank: Super Contributor
timestamp: April 27, 2023, 12:53:40 am
content: took 3 seconds to find it loll34401A-06SUPERSEDES: NoneContinuedDATE: January 199634401A MultimeterSerial Numbers: 0000A00000 / 9999Z99999Display assembly replacement requires compatible firmware.To Be Performed By: Agilent-Qualified PersonnelParts Required: See belowSituation:Display segments may degrade with time. Service action is appropriate if it becomes diffi-cult to read the display from a distance of two meters. Either replace the display assemblyor replace the display itself.Page 2ServiceSolution/Action:Replace the display assembly with a compatible assembly or replace the display. Thedisplay, P/N 2090-0296, is a vacuum fluorescent display and is a through-hole part with34 leads.Compatibility between display assemblies and the main assembly is determined by theversion of firmware installed in the product (firmware version for a 34401A determinedby entering the SYSTEM MENU and on the COMMAND level moving across to8:REVISION and down to display the Version).Assembly/part 34401-66502 34401-66512 2090-0296(description) (Front Panel pc (Front Panel pc (Display, Vacuum-Assembly) Assembly) Fluorescent)CompatibleFirmware Version: 06-04-01 Version: 06-04-02 Version: alland lower and higher

author: Miti
author_rank: Super Contributor
timestamp: April 27, 2023, 05:52:36 pm
content: I tried Google and DuckDuckGo and no one can find any of these service notes.

author: Hydron
author_rank: Super Contributor
timestamp: April 28, 2023, 06:23:35 am
content: First link on Google (to a PDF hosted on eevbog) for me

author: Miti
author_rank: Super Contributor
timestamp: April 28, 2023, 10:18:24 am
content: Quote from: Hydron on April 28, 2023, 06:23:35 amI think Google is playing funky with me. I tried again, it finds this one posted by coromonadalix yesterday and nothing else. DuckDuckGo doesn’t even find this one. They find service and user manuals galore but no service notes. I think we see different results based on the region? Can you find other service notes, 34401A-08 for example?

author: coromonadalix
author_rank: Super Contributor
timestamp: April 28, 2023, 10:51:01 am
content: loll this one just popped this text with notes in it ??11-05-02AgilentGray Shift buttonBlack and red terminalsSerial MY4xxxxxxxManufactured 2005Main board 34401-66511 REV 003Blue Meder Reed relay10-05-02HPGray Shift buttonRed terminalsSerial US3xxxxxxxManufactured 1998Main board 34401-66501 REV DRed Coto Reed relay07-05-02HPBlue Shift buttonRed terminalsSerial 3xxxAxxxxxManufactured 1995Main board 88809F 34401-66501 REV BRed Coto Reed relay05-01-01HPBlue Shift buttonRed terminalsSerial unknownManufactured 1995Main board 88809F 34401-66501 REV BRed Coto Reed relayFuses (not specified in the service or user manual):F7A Littelfuse 314F3A Littelfuse 235T250mA Schurter FSD (early units might be installed with T125mA for linevoltages >=220V AC (as are Keithley 20x0 units for these voltages))The 34401a CPU FW can be written to the same FLASH EEPROMs that also work forKeithley 2000 and 2010: SST39SF020A-70. An upgrade generally requiresdesoldering of the CPU FW ROM and (if you are a risk-averter) mounting ofa 32-pin PLCC socket. Some FW upgrades benefit from an EEPROM contentupgrade as well (or it might be necessary) - see below.According to HP Service Note 34401A-06, the front panel assembly34401-66502 works with firmware 06-04-01 and lower. 34401-66512 works with06-04-02 and higher.The latest code AFAIK is 11-05-03. XX-ZZ-03 is for the third generation offront panel assembly that is a direct replacement to -02. It is unclear ifit also is compatible to units that were using -01 (but at least from05-01-01 it can be upgraded to XX-05-YY).As main board 88809F 34401-66501 REV B is used for both 05-01-01 and07-05-02, the communications processor can be upgraded to versionXX-01/02/03/04-YY to XX-05-YY. (This code can AFAIK not be downloaded.)The EEPROM structure looks the same from 07-05-02 to 11-05-02, so nocalibration seems to be necessary when upgrading FW from 07-05-02 to11-05-02.The EEPROM structure of 05-01-01 is different from 07-05-02, but it seemsthat overwriting EEPROM of 05-01-01 with EEPROM of 07+-05-02 works(although calibration is definitely needed afterwards).Service note 34401A-07 says that communications processor XX-03-YY andXX-04-YY suffer from RS232 error and an upgrade to XX-05-YY isrecommended.Service note 34401A-08 says that communication processor XX-02-YY,XX-03-YY, and XX-04-YY suffer from a GPIB error and an upgrade to XX-05-YYis recommended.Service note 34401A-09 says that CPU FW 06-AA-BB in some units suffersfrom an "erroneous overload" error and an upgrade is recommended in thiscase.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 28, 2023, 11:03:55 am
content: and found theses

author: HighVoltage
author_rank: Super Contributor
timestamp: April 28, 2023, 11:10:06 am
content: Go to the Keysight Service Notes website:https://support.keysight.com/s/service-notes?language=en_USand type "34401A" into the search field and you will get all service notes for this instrument.

author: Miti
author_rank: Super Contributor
timestamp: April 28, 2023, 03:52:00 pm
content: Quote from: HighVoltage on April 28, 2023, 11:10:06 amThanks, that works… on my laptop at work. Zero service notes on my phone. I’ll check from home tonight.Edit: It gets even more interesting. If I connect to internet using my LTE data, it doesn’t find any service notes. If I turn on the Wi-Fi and connect to the company internet, it finds all 14 service notes. Craaazy…

author: GigaJoe
author_rank: Frequent Contributor
timestamp: April 29, 2023, 03:26:18 pm
content: more likely you phone browser behavior, cutting some script.

author: Peter_O
author_rank: Frequent Contributor
timestamp: May 09, 2023, 11:48:53 am
content: I've bought this one:https://de.aliexpress.com/item/1005003371396426.htmlfor 34 Euros incl. tax and shipping and received it 2 weeks later via DHL in Germany well packed in a small cardboard parcel.

author: Hydron
author_rank: Super Contributor
timestamp: May 09, 2023, 12:35:34 pm
content: Mine (same seller) is out for delivery now... but Evri (aka Hermes, name change probably aimed at tricking people who've had bad Hermes experiences) is indicating that they're going to try and deliver to my work address (clearly a business) between 5 and 7pm, so it'll be closed and I'll need to wait a while longer before reporting back on my orderEdit: it showed up, was also well packed (important as the box had taken a beating) and looks to be in good new condition. Will report back once I've installed it, might be a few days until I have a chance though.

author: Hydron
author_rank: Super Contributor
timestamp: May 10, 2023, 07:12:24 pm
content: Found some time to put it in my meter, results were in line with Miti's (i.e. good brightness and evenly lit). Don't have a before photo unfortunately and not much point in an after one (will look like Miti's).Examining my original VFD (Samsung) vs the Aliexpress clone shows some pretty close copying going on; the main differences I could see were some slight differences in the phosphor (Samsung was a bit whiter), and the grid infront of the anodes was a bit finer on the original (i.e. a bit higher quality).Zero issues getting it installed - a good desoldering iron makes short work of it (the VFD was one of the easiest many-pin devices I've ever desoldered, due to it's long flexible pins and large hole clearances) and my original display should still work fine if I ever need it as a backup.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 11, 2023, 05:21:21 pm
content: check the other thread early 34401a revision lolll number 42 loll

author: hp3310a
author_rank: Regular Contributor
timestamp: January 18, 2025, 06:21:43 pm
content: Old thread I know but it seems to me it's most appropriate here and people here don't like thread creep as far as I can tell...On the topic: I'm obsessing with the idea of getting a 34401a and came across a unit that looks interesting. It has a "MY41...." serial number so I guess it's from the early 2000s and red/black plugs on the front but red-only plugs (no black) on the rear.I looked at a lot of units on ebay and I found none that have a black/non-black plug combination. Has there been a time where the 34401a was manufactured like that?

author: coromonadalix
author_rank: Super Contributor
timestamp: January 18, 2025, 06:33:31 pm
content: get a 34410a instead ? and update your avatar position, would help a biton ebay.com there are 34401a with red blacksome fromchina at 360USD right now 2025 01 18 ??japan at 400USDeven some start bid at 200USD ?

author: hp3310a
author_rank: Regular Contributor
timestamp: January 18, 2025, 07:51:09 pm
content: Not sure what you're replying to, my question was this: Was there ever a version built that had red+black plugs on the front panel, and red-only plugs on the back?

author: AVGresponding
author_rank: Super Contributor
timestamp: January 18, 2025, 09:56:08 pm
content: Quote from: hp3310a on January 18, 2025, 07:51:09 pmVery,veryunlikely. These are well known for chimera builds, that is the likely explanation. Chances are it'll be near impossible to establish without the thing in your possession.

author: Hydron
author_rank: Super Contributor
timestamp: January 18, 2025, 11:04:04 pm
content: Malaysia unit means it'll have the newer display which is good, and if you're lucky it'll have FW v7 or later which means extra hidden features can be enabled.

author: dimmog
author_rank: Regular Contributor
timestamp: January 18, 2025, 11:04:38 pm
content: Quote from: hp3310a on January 18, 2025, 06:21:43 pmHP/Agilent has never produced the 34401A with different terminals on the front and rear. I refer to such units as "Frankenstein" because it's possible that the terminal block was replaced, or an older main board with replaced block was installed in a newer 'MY' chassis and so on.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 19, 2025, 04:11:51 am
content: yep my bad and yes the red / black jacks where orderable at some pointyou would have an "Franken meter" as other wrote, full red or black /red meters if doubts you check the FW version, or unless some play dirt tricks ?and yes the MY xxxx units where black /red

author: hp3310a
author_rank: Regular Contributor
timestamp: January 19, 2025, 05:29:43 pm
content: OK, thanks that doesn't appear to be a good specimen then (the one I was looking at).

author: AVGresponding
author_rank: Super Contributor
timestamp: January 20, 2025, 10:26:15 am
content: Quote from: hp3310a on January 19, 2025, 05:29:43 pmDepends on the price and whether it passes self-test

author: coromonadalix
author_rank: Super Contributor
timestamp: January 20, 2025, 10:57:00 am
content: when possible and the seller accept it ... ask for a selftest screen and the FW version on the display ...for the latest xx v11 xx fw keysight was selling the chip, but the fw leaked on the web and you buy a new ic, and program it ..

author: hp3310a
author_rank: Regular Contributor
timestamp: January 20, 2025, 11:46:45 am
content: The firmware revision of the unit in question is 06-04-01, the price over $460. According to the seller, this unit was combined by using an banged up old unit's board with one with a dead board but newer chassis. So the serial isn't the one from the board. I think I'll let someone take a chance on this one.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 20, 2025, 11:57:20 am
content: yep and that price pfffff way too muchsome are still trying to pull a profit .. they usually sit around 400$ usd or lessand nowadays some 34410a have gone out between 450$ 560$ witch is a superior model, w more connectivity ... aka 34401a replacement w faster measurements, 34411a witch is faster than 34410a price(s) began to drop toojust the small fan in them who could be a nag, sometimes they hiss ...34401a was a reference but other exists

author: ps
author_rank: Regular Contributor
timestamp: January 20, 2025, 07:33:30 pm
content: Did anyone dump the IO firmware, is it available on the net?Update: KO4BB has it,http://w.ko4bb.com/getsimple/index.php?id=manuals&dir=HP_Agilent_Keysight/HP_34401A_6.5_Digit_Multimeter. Some server problems at the moment, but generally it is there.According to Service Note 34401A-06, CPU firmware 06-xx-xx is the last one that supports the old VFD PCB xx-xx-01 and also the first one that supports the new xx-xx-02. CPU FW 06-xx-xx usually comes with IO FW xx-04-xx, but Service Note 34401A-08 indicates that this can be substituted with xx-05-xx without any issues. So 06-05-01 should be fine with the old display.Did anybody try to combine CPU FW 07-xx-xx or later with a xx-xx-01 display?

author: AVGresponding
author_rank: Super Contributor
timestamp: January 21, 2025, 06:09:44 pm
content: Insane price, for what it is... a late Agilent version just sold for £240 + shipping on UK ebay...