Agilent 34401A 2w drift and high readings when power up - Page 1
Forum section: electronics / repair

author: yo0
author_rank: Regular Contributor
timestamp: June 20, 2017, 04:00:14 pm
content: Hello, i have a recently adquired a very nice and clean $200.00usd Agilent 34401a, everything works good but 2w ohms, i already dissasembled and clean S1 swith, by the way it was already very clean and shiny both contacts and whipers, i checked every 24k resistor and they measure good in every series combination and contacts possible and values are right 24k 48k 72k in all of the 12 resistors (front and rear) so no bad contacts or cracked solders, both front and rear exhibit very close readings, when turning on with shorted 2w, a reading of almost 9 ohms is obtained and with time decrease, after 2-3 hours reach 0.05 ohms aprox. during this time both front an rear decrease readings in very similar values. null zeroing drifts too.from the begining all tests pass,i already reflow S1 switch, inputs, k101 relay, cleaned inputs with deoxit and cotton sticks, no luckheat affecting components?, transistor ladder(4w works good, only last digit moves a bit, maybe pomona minigrabers fault) ?any clues?any help will be really appreciated.best regards.Pio

author: mzacharias
author_rank: Frequent Contributor
timestamp: June 20, 2017, 04:45:33 pm
content: I had a problem of drifting Ohms values on a Fluke 8840. Turned out to be the push-on connectors at the rear of the front panel jacks (I never tried the rear). The "female" end seemed to be a different metal than the "male" end at the jack side, and looked as if there was a powdery "zinc-oxide" type of coating had formed. Cleaning these and applying De-Oxit fixed the problem. Any type of series resistance will cause this problem on Ohms function, but will not affect voltage readings. Oh - and don't rule out a relay issue.

author: yo0
author_rank: Regular Contributor
timestamp: June 20, 2017, 04:55:22 pm
content: Quote from: mzacharias on June 20, 2017, 04:45:33 pmi hope the relay is good, i am kind of newbie in this hobby, how to test/check the relay?best regardsPio

author: HighVoltage
author_rank: Super Contributor
timestamp: June 20, 2017, 08:58:36 pm
content: Search the forum for "Agilent 34401A Ohm"There is lots of really good info around from others who had a similar problem.Like this one:https://www.eevblog.com/forum/repair/34401a-2w-ohm-strange-phenomenon/msg516253/#msg516253

author: yo0
author_rank: Regular Contributor
timestamp: June 20, 2017, 10:25:07 pm
content: i discover k101 relay, tapping it several times with a pencil (rubber side) the readings go down and down with every tap received to a minimun of 0.013 ohms, will check all nearby solders, hope relay is not the culprit, think is no easy available, maybe a substitute with a fixture in the worst case?i think i will remove it and make extentions with wires for the next tapping sessionbest regardsPio

author: yo0
author_rank: Regular Contributor
timestamp: June 21, 2017, 06:53:58 pm
content: relay K101 the culprit, now i need find a suitable replacement, if i pull it up, the resistence goes up and if press down goes down, probably relay internal damaged solder. anybody know a good suitable replacement?best regardsPio

author: HighVoltage
author_rank: Super Contributor
timestamp: June 21, 2017, 09:21:32 pm
content: Congratulations on finding the problem.The relay is made by COTO (P-0214)Agilent / Keysight part number:0490-1914http://www.keysight.com/my/faces/partDetail.jspx?partNumber=0490-1914&_afrLoop=320964009740000&_afrWindowMode=0&_afrWindowId=oyi344oef_10#%40%3F_afrWindowId%3Doyi344oef_10%26_afrLoop%3D320964009740000%26partNumber%3D0490-1914%26_afrWindowMode%3D0%26_adf.ctrl-state%3Doyi344oef_22I gave up on sourcing this relay somewhere else and bought it directly from keysight, because nothing comparable was available.May be you have better luck, let us know.

author: yo0
author_rank: Regular Contributor
timestamp: June 21, 2017, 10:24:17 pm
content: Quote from: HighVoltage on June 21, 2017, 09:21:32 pmthank you, already search at digi-key and mouser, no luck haha, so i think no option other than Key$ight, by the way, is common relay failure in this DMM model?ps.attached related datasheets...best regards.Pio

author: carl_lab
author_rank: Frequent Contributor
timestamp: June 22, 2017, 09:43:50 am
content: Quote from: yo0 on June 21, 2017, 10:24:17 pmWe had some relay failure (the smaller yellow ones) in this DMM and other models.But they are much cheaper and better available than the COTO relay.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 22, 2017, 11:38:33 am
content: This relay usually does not fail, probably only when the voltage is far too high, like 2000 Volts applied or so.I had 2 defect relays over the years, one in a 34401A and one in a 34410A. Both of these DMMs I bought used and broken, so I am not sure, what the cause of failure was.But after endless searching, the only source was from Keysight.Meder was not allowed to sell this item, since it was exclusive to Keysight.

author: yo0
author_rank: Regular Contributor
timestamp: June 22, 2017, 01:26:15 pm
content: Thank you, what are the simptoms lead you to identify the relay as bad?Best regards.Pio

author: HighVoltage
author_rank: Super Contributor
timestamp: June 22, 2017, 02:48:00 pm
content: Quote from: yo0 on June 22, 2017, 01:26:15 pmYou can read it all here:https://www.eevblog.com/forum/repair/agilent-34410a-repair-attempt-of-2-dead-meters/These relays are very special, made for the 1000 V range.

author: yo0
author_rank: Regular Contributor
timestamp: June 23, 2017, 03:04:17 am
content: thank you again, i already remove the relay, i feed it with my ps at 5vdc and to my Fluke dmm, it measures aprox 0.13 ohms after aprox 30 minutes the reading reach 1.6 ohms, i think it is not normal, do you agree with me? we can say now it is defective?ps.if i hold it with my hand the body heat make the reading decreasebest regards.Pio

author: carl_lab
author_rank: Frequent Contributor
timestamp: June 23, 2017, 05:34:32 am
content: Quote from: yo0 on June 23, 2017, 03:04:17 amI also think it's not normal.How does it react when you knock on the relay?

author: yo0
author_rank: Regular Contributor
timestamp: June 23, 2017, 05:48:14 am
content: No change, but mounted in pcb de readings change, maybe the near smaller relays (3) or other component are affected by the tapping, but i think the others relays are not involved in 2w measurement, maybe i am wrong.Now i am confused haha!Best regardsPio

author: floobydust
author_rank: Super Contributor
timestamp: June 23, 2017, 06:01:14 am
content: I've seen reed relays get sticky contacts with age, the contacts seem to get magnetized. The DIP style ones anyway.I take a cassette tape head demagnetizer to them and they work fine afterwards. Strange but works for me.

author: yo0
author_rank: Regular Contributor
timestamp: June 23, 2017, 02:30:32 pm
content: And at this morning this is the reading at start upBest regardsPio

author: HighVoltage
author_rank: Super Contributor
timestamp: June 23, 2017, 05:08:07 pm
content: It looks like you definitely need a new relay.

author: yo0
author_rank: Regular Contributor
timestamp: June 23, 2017, 05:40:25 pm
content: Quote from: HighVoltage on June 23, 2017, 05:08:07 pmi think so, Key$ight is waiting for methank you to all for all your help and opinions.ps.@HighVoltage do you think this could work?Quote from: floobydust on June 23, 2017, 06:01:14 ambest regardsPio

author: carl_lab
author_rank: Frequent Contributor
timestamp: June 23, 2017, 07:40:00 pm
content: Quote from: yo0 on June 23, 2017, 02:30:32 pmBatteries of your Fluke handheld are OK?

author: yo0
author_rank: Regular Contributor
timestamp: June 23, 2017, 07:45:45 pm
content: Quote from: carl_lab on June 23, 2017, 07:40:00 pmyes i think, at least the battery icon is off, i will put a fresh one just to be sure the readings are ok.good pointbest regardsPio

author: yo0
author_rank: Regular Contributor
timestamp: June 24, 2017, 12:16:41 am
content: Quote from: yo0 on June 23, 2017, 07:45:45 pmSame reading with fresh battery. And with another fluke 87vPío

author: Samogon
author_rank: Frequent Contributor
timestamp: June 24, 2017, 04:43:23 am
content: Quote from: yo0 on June 23, 2017, 05:40:25 pmIn theory1 This relay has conductive maybe even ferromagnetic casing2 Alternating magnetic field will induce Eddy currents in the casing which then cause heating of casing and will not reach internal components

author: yo0
author_rank: Regular Contributor
timestamp: June 24, 2017, 05:30:03 am
content: Quote from: Samogon on June 24, 2017, 04:43:23 amThank you, i was thinking about shield in the case, but you give more info, thank you.What about applying enough heat to the terminals to reflow internal connections?I read about this ( i think risky) technic in yahoo groups.https://groups.yahoo.com/neo/groups/hp_agilent_equipment/conversations/topics/37392Pio

author: Samogon
author_rank: Frequent Contributor
timestamp: June 24, 2017, 12:41:32 pm
content: Just bite the bullet and buy damn relay

author: Samogon
author_rank: Frequent Contributor
timestamp: June 24, 2017, 01:12:31 pm
content: Btw keysight will not sell you any if you are not buying via corporate account.In my case i was politely sent into erotic hiking.

author: yo0
author_rank: Regular Contributor
timestamp: June 24, 2017, 01:14:58 pm
content: Yes, waiting Monday to call keysight

author: HighVoltage
author_rank: Super Contributor
timestamp: June 24, 2017, 01:46:10 pm
content: I took the relay of my 34410A apartHere are the tear down pictures again, since we talk so much about this relay.

author: yo0
author_rank: Regular Contributor
timestamp: June 24, 2017, 03:00:15 pm
content: Quote from: Samogon on June 24, 2017, 01:12:31 pmops! when you say corporate account do you mean ANY company? and no sells to individuals?best regardsPio

author: Samogon
author_rank: Frequent Contributor
timestamp: June 24, 2017, 04:05:36 pm
content: Yes, no sales to individuals

author: yo0
author_rank: Regular Contributor
timestamp: June 24, 2017, 04:12:30 pm
content: Quote from: Samogon on June 24, 2017, 04:05:36 pmthank you, i need to be creative when talk with them.best regardsPio

author: Samogon
author_rank: Frequent Contributor
timestamp: June 24, 2017, 04:48:36 pm
content: Not gonna flyThey will ask for payment method and delivery address to be a company

author: yo0
author_rank: Regular Contributor
timestamp: June 24, 2017, 04:55:43 pm
content: Quote from: Samogon on June 24, 2017, 04:48:36 pmyes i know that, let see Mondayi´ll keep you informedPio

author: yo0
author_rank: Regular Contributor
timestamp: August 01, 2017, 04:49:34 am
content: since the relay most common failure is mechanical related, just did a reflow on the removed from pcb k101 relay (aprox 330°c about 20-25 seconds) in both relay reed pins, reinstalled to pcb and it is working stable as should be again for several weeks, hope this help somebody.another option is the coto 3501-05-91X, the only trade off is the maximun voltage is reduced to about half (think is more than adequate for most people needs), the other functions operation limits are almost the same, but this part number is much more available than the heaftier model 3540-05-91xupdate: Feb 5, 2023, unit still working fine!best regardsPio

author: pete99
author_rank: Contributor
timestamp: November 07, 2017, 05:11:09 am
content: Hi,I also have a bad k101 relay. I tried to purchase from Keysight but I was rejected because I no longer have a company email. I am a retired test engineer from an aerospace/defense company, that purchased hundreds of thousands of dollars in HP and Agilent test equipment over my career and get rejected to purchase a $50 part. Pretty funny. I've contacted Coto in Germany and they referred me to Keysight.Do you have any other suggestions?Thanks so much,Steve

author: HighVoltage
author_rank: Super Contributor
timestamp: November 07, 2017, 07:50:23 am
content: Quote from: pete99 on November 07, 2017, 05:11:09 amSteveI have tried to buy from Coto for years and it is not working, because this special relay was built for Agilent/Keysight only. I have ended up, buying it from Keysight directly.Send me a PM.

author: pete99
author_rank: Contributor
timestamp: November 07, 2017, 08:35:15 pm
content: Thanks for the reply. I sent a message to Keysight sales, so waiting to see how they respond. In the meantime, I went ahead and ordered a Coto suggested substitute from Testco, the 3540-05-911. One of it's ratings is 500v instead of the Keysight 1000v rating which doesn't concern me. I'll let you know how it works out. Do you use the 34401 at home or at your job (or both)?All the best,Steve

author: HighVoltage
author_rank: Super Contributor
timestamp: November 08, 2017, 08:11:05 am
content: I have plenty of 34401A instrument and use them at work and at customer places installed in test stands and also a few at home for hobby use. They are great and reliable for many years, if treated well.

author: pete99
author_rank: Contributor
timestamp: November 10, 2017, 08:07:29 pm
content: Here is the current status of my 34401A Relay repair.I ordered and received the Coto relay from Testco (distributor). The part number is 3540-05-911. I think it was approx $32 US. It is rated at 500v instead of the HP/Keysight rating of 1000v. It has an extra pin between the two coil pins. Not sure what it's connected to, I just bent it over. I installed the relay and after testing and running for 2 days, it appears to be working just fine.In the meantime, I had sent an email to Keysight sales and they replied with a quotation. So I went ahead and made up a purchase order and emailed it back to them (usa_orders@keysight.com, they probably have an address for overseas orders). I was asked to call (800 829-4444) to agree with their terms and supply a credit card number. They ship 2 day delivery at no charge. They have a $50 US minimum, but this part price is $52.86 US, so all appears to be good.Thanks again for your help,Steve