Q:  Agilent/HP 34401a versions,  is any particular one preferable? - Page 1
Forum section: electronics / testgear

author: dorkshoei
author_rank: Frequent Contributor
timestamp: December 18, 2020, 05:48:31 pm
content: Hi.I'm looking to pickup an 34401a. I stupidly wasn't paying attention andmissed this one for sale here.I'm wondering if any particular version (other things like price, brightness of VFD etc being equal) should be preferred over another?I'm aware of at least the following variants:- Original HP style without rubber bumpers.- Later HP style with rubber bumpers, all red jack connectors.- Agilent style which is very similar to the later HP but the jacks are red and black.- Later Agilent version that has an oval shift button.I'd heard that some of the units use VFD driver chips that are now unobtanium. Obviously eventually Keysight will probably obsolete all parts. I'm aware that the VFDs themselves (not the drivers) are available as Chinese clones.Advice appreciated.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: December 18, 2020, 09:21:57 pm
content: I should have searched more before asking.I found this:https://www.eevblog.com/forum/testgear/agilent-34401a-revisions/Full of excellent advice.So are the USA made units likely to have the 01 display pcb?

author: masterx81
author_rank: Frequent Contributor
timestamp: December 18, 2020, 09:59:29 pm
content: take a look here:https://www.eevblog.com/forum/testgear/agilent-34401a-revisions/Quote

author: dorkshoei
author_rank: Frequent Contributor
timestamp: December 18, 2020, 10:16:11 pm
content: @masterx81 thanks for the reply; see my post above yours, I already found that.The trailing -01 and -02 are the version of the display pcb.I understand you can obtain the version from the menu but can you conclude anything about likely display version based on the type of the unit and country of manufacture?I assume the early HP unitslike this pictured unithave -01 display pcb?All thelater HP units I've seen(rubber bumpers) have been marked "made in USA".All theAgilent rubber bumper unitsI've seen have been marked "made in Malaysia". On the above referenced thread someone said their Malaysia made Agilent had -02.

author: masterx81
author_rank: Frequent Contributor
timestamp: December 18, 2020, 11:41:12 pm
content: I have a late HP unit with rubbers and red plugs, with "newer" firmware. I've not opened mine but hopefully have the "easy to find" vfd.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: December 19, 2020, 06:40:10 pm
content: So the service manual (page 138; backdating) specifies the serial# of the display pcb changeover.the old display pcb: 34401-66502 (which shows as -01 in the last digit of the firmware) is 3146A59641 and lowerAFAICT the xxxxAyyyyy format is only used in the older units and so I assume anything with the newer format of {US/MY/SG}XXYYYYYY should have the newer display pcb.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: December 19, 2020, 06:43:14 pm
content: So this pictured unit will have the older -01 display pcb

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: December 19, 2020, 07:10:23 pm
content: Back to your original question, I am not aware of any reason why an older serial makes it better. I suggest you to go with the latest serial if all else is equal.A few things to consider:- if you don’t like dim and uneven display, any display work will set you back $75-150+- Current calibration in the US is worth $100+, depending on cal shop available in your area. If it is an unit without cal history, you probably would want a cal report with adjustment if you want accuracy along with 6.5 digit precision.- If you want it to look nice cosmetically, front lens, keypads, and cover will set you back $100+- Button style is a matter of preference, I had both in the past, and end up letting go the oval button version and kept two of the late model square button version.- Bumper is a very good thing if you stack equipment without a 19” rack. It leaves a little air gap between units.Like buying a house. My suggestion is if you wants something that works well and looks decent, pay a little more to get one in that condition, as parts are expensive.Good luck, I love the 34401A, I use them when silence is important, and they are built to last forever. For most hobby use, once you do a fresh cal and adjustment, you probably don’t need to touch it for 5 years.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: December 19, 2020, 07:22:27 pm
content: Quote from: NoisyBoy on December 19, 2020, 07:10:23 pmYou read my assumption backwards. I was assuming older serial was less desirable.

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: December 19, 2020, 09:41:32 pm
content: Then I agree with your position.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: December 19, 2020, 10:28:30 pm
content: Quote from: dorkshoei on December 19, 2020, 06:43:14 pmThe above is one of the older units without the rubber bumpers. I just found this pictured item on eBay. Perhaps it's possible to retrofit the rubber bumpers onto the older style units? Either way, based on the 3146A59641 serial number cutoff, this should also have the older -01 display pcb.

author: masterx81
author_rank: Frequent Contributor
timestamp: December 20, 2020, 01:10:49 am
content: Mine with s/n US36060233 have same rubbers and fw 09-05-02. Look identical to that one

author: coromonadalix
author_rank: Super Contributor
timestamp: December 20, 2020, 02:48:26 am
content: Older versions are less desirable if you have leaking vfd drivers ... for the recent versions, you can find the vfd drivers ic's if needed BUT the vfd alone isn't available at Keysight, I have an account there.And the most noticeable difference(s) is the front panel look, you can change the old models look if you order the front / rear and power switchs levers, the rubber / flubber keypad, the front panel and the black windows bezel.Edit: you'll be stuck with the red plugs ... for the old series.For vfd repairsYou have to order the complete pcb / vfd assembly for a mere 200$ usd, and you may have firmware incompatibilities if used in the "old" models Hp Agilent models Keysight said to me ??And they told me, they dont have a ton leftAnd if you can find any Samsung branded spare vfd, you may have a genuine one if the seller can proove it, or you can assume there all clone of the original one

author: dorkshoei
author_rank: Frequent Contributor
timestamp: December 22, 2020, 04:19:30 pm
content: coromonadalix thanks for the info.So does anyone know how to decode the serial numbers? Someone tangential but I'm curious.It seems like there is an old format: xxxxAyyyyy and a new format {US/MY/SG}XXYYYYYY

author: openloop
author_rank: Regular Contributor
timestamp: December 22, 2020, 05:40:31 pm
content: On old vs new:In "oval buttoned" 34401A, then Agilent has redesigned the instrument's front end.I believe due to the part availability, they've replaced classic dual JFET with a bootstrapped op-amp.It's anecdotal, I know, but comparing to an older unit I have, the instrument is noticeably worse.Maybe there are more differences, but it is noisier and have higher temp co.Linearity is suspect too - you cannot rely on test results other people posted simply because it's practically a different instrument now.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 23, 2020, 12:01:08 am
content: the only thing i know for theses puppiesThe front panel revision in firmware: the official version 11 fw is not available (at the time i asked), you had to send the meter at Keysight for an upgrade, it was leaked here in some 34401a threads, there was some parts change if i recall on the front pcb Ie: vfd drivers is the most obviousBut i think the main pcb was mostly unchanged (i may be wrong, surelyopenloopis right) i did saw some people put a foam on the lm399 to stabilise temperature driftsBut it's a closed casing.All my meters had the lytics and tantalums changed one year ago, and the last one who's been recenlty sold had a clone Vfd (Aliexpress) and was not calibrated, the others two where in specs (but at lower or higher limits in some range) and calibrated after the capacitors change.After 1hr of warm up they where stable and rock steady ?Now i need some place ... i'm getting old lollMe too i'm curious by the numbering scheme

author: Robaroni
author_rank: Frequent Contributor
timestamp: December 23, 2020, 11:55:28 pm
content: I just posted a thread on the NOS 34401A I bought. I did a little prelim testing comparing it to my 34465A which is almost spot on in cal. After sitting in a box for ten years or more the 34401A was within 200uV of the 34465A. It is the newer version made around 2009/10 and has the 11-05-03 firmware, oval shift, etc. made in Singapore. What a little gem this meter is, takes me back to the days of HP when HP was HP.I expect to get lots of years out of it.

author: Robaroni
author_rank: Frequent Contributor
timestamp: December 24, 2020, 12:45:16 am
content: What's the "H01" option? I couldn't find it anywhere.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 24, 2020, 05:17:24 pm
content: what H01 option ? never heard of this, whre did you find that or see that ?

author: Robaroni
author_rank: Frequent Contributor
timestamp: December 24, 2020, 07:15:58 pm
content: On my NOS meter.Check my thread:https://www.eevblog.com/forum/testgear/new-agilent-34401a-meter/new/?topicseen#new

author: alm
author_rank: Super Contributor
timestamp: December 24, 2020, 07:48:47 pm
content: Option H01 is used for all kinds of modified specs (different bandwidth, power levels, average-responding AC, etc). For the 3458A, it's that it measures up to 1000 VAC, instead of 750 VAC. It likely is some specific change in specifications for some major customer. Does it do average-responding AC (either instead of true RMS or as option)? I think the military needed this for some of their procedures for equipment that may not be replaced as often as test equipment, like planes or ships. TheKeithley 2001M supported average-responding ACover the normal 2001 for that reason. Or maybe it's for 400 Hz operation?According to thishuge article on test equipment(scroll down to HP 332A), option H01 "usually means it was built for the telephone company or some Government agency". So I guess that's consistent with these made especially for the Navy.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 24, 2020, 10:06:55 pm
content: ooooo kay never saw this specification(s), a warning of 60hz and 180hz emanations who could interfere with sensitive equipment near the meterIt would have been possible to use an toroid x-former instaed of an laminated one, that would have killed some emanations ?? with a copper shielding around it, it would have been (almost) perfect ?@robaroni would it be possible just to unscrew the top casing and show us the inside without touching anything else, like having nytrile gloves and antistatic protection(s)

author: Robaroni
author_rank: Frequent Contributor
timestamp: December 24, 2020, 10:25:46 pm
content: I'll see what I can do, after all it won't void the warranty!!

author: Robaroni
author_rank: Frequent Contributor
timestamp: December 24, 2020, 10:33:24 pm
content: Thanks, I couldn't find any specifics on the option.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: December 25, 2020, 06:58:26 pm
content: Can anyone clarify the following?The firmware version displayed is AA-BB-CC. My understanding is that: AA: measurement processor revision; BB: i/o processor revision; CC: front panel processor revisionSo if I look at34401 service note 6it implies that "06-04-01" and "06-04-02" are distinct firmware versions. So does each refer to a specific version of the EPROM at U502?The reason I'm confused is the backdating section of the service manual says serial "3146A59641" and earlier uses v01 of the display pcb but there is no corresponding serial number range for U502

author: Trader
author_rank: Frequent Contributor
timestamp: December 25, 2020, 11:00:42 pm
content: Quote from: dorkshoei on December 18, 2020, 05:48:31 pmhttps://www.ebay.com/itm/HP-Agilent-34401A-6-1-2-Digit-Digital-Multimeter-3/154259941202

author: coromonadalix
author_rank: Super Contributor
timestamp: December 25, 2020, 11:49:44 pm
content: Quote from: dorkshoei on December 25, 2020, 06:58:26 pmNot sure is it the other way around, i was told the display fw version was the first IE : 11-05-02 ??At keysight the last display fw version was 11I stand corrected thks for the following post video

author: dorkshoei
author_rank: Frequent Contributor
timestamp: December 26, 2020, 12:01:06 am
content: Quote from: coromonadalix on December 25, 2020, 11:49:44 pmOfficial videohttps://youtu.be/30zq8F1CirsGiven that tthere are two different display versions, 01 and 02 in last position seems also obviously correct [edit, I'd forgotten there is a third version on the final keysight branded units]

author: Robaroni
author_rank: Frequent Contributor
timestamp: December 26, 2020, 12:21:27 am
content: Quote from: coromonadalix on December 24, 2020, 10:06:55 pmI'll have to wait a bit, there is warranty from the seller.