Agilent 34401A 2w drift and high readings when power up

[yo0]

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 luck

heat 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

[mzacharias]

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.

[yo0]

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.

i hope the relay is good, i am kind of newbie in this hobby, how to test/check the relay?

best regards


Pio

[HighVoltage]

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

[yo0]

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 session

best regards


Pio

[yo0]

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 regards


Pio

[HighVoltage]

Congratulations on finding the problem.

The relay is made by COTO (P-0214)
Agilent / Keysight part number: 0490-1914

http://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_22

I 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.

[yo0]

Congratulations on finding the problem.

The relay is made by COTO (P-0214)
Agilent / Keysight part number: 0490-1914

http://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_22

I 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.

thank 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

[carl_lab]

...by the way, is common relay failure in this DMM model?

We 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.

[HighVoltage]

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.

[yo0]

Thank you, what are the simptoms lead you to identify the relay as bad?


Best regards.


Pio

[HighVoltage]

Thank you, what are the simptoms lead you to identify the relay as bad?

Best regards.
Pio

You 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.

[yo0]

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 decrease




best regards.


Pio

[carl_lab]

... 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?

I also think it's not normal.
How does it react when you knock on the relay?

[yo0]

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 regards


Pio

[floobydust]

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.

[yo0]

And at this morning this is the reading at start up



Best regards


Pio

[HighVoltage]

It looks like you definitely need a new relay.

[yo0]

It looks like you definitely need a new relay.

i think so, Key$ight is waiting for me 


thank you to all for all your help and opinions.

ps.

@HighVoltage do you think this could work?

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.

best regards


Pio

[carl_lab]

And at this morning this is the reading at start up

Batteries of your Fluke handheld are OK? 

[yo0]

And at this morning this is the reading at start up

Batteries of your Fluke handheld are OK? 

yes i think, at least the battery icon is off, i will put a fresh one just to be sure the readings are ok.

good point 


best regards


Pio

[yo0]

And at this morning this is the reading at start up

Batteries of your Fluke handheld are OK? 

yes i think, at least the battery icon is off, i will put a fresh one just to be sure the readings are ok.

good point 


best regards


Pio

Same reading with fresh battery. And with another fluke 87v


Pío

[Samogon]

It looks like you definitely need a new relay.

i think so, Key$ight is waiting for me 


thank you to all for all your help and opinions.

ps.

@HighVoltage do you think this could work?

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.

best regards


Pio

In theory
1 This relay has conductive maybe even ferromagnetic casing
2 Alternating magnetic field will  induce Eddy  currents in the casing which then cause heating of casing and will not reach internal components

[yo0]

It looks like you definitely need a new relay.

i think so, Key$ight is waiting for me 


thank you to all for all your help and opinions.

ps.

@HighVoltage do you think this could work?

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.

best regards


Pio

In theory
1 This relay has conductive maybe even ferromagnetic casing
2 Alternating magnetic field will  induce Eddy  currents in the casing which then cause heating of casing and will not reach internal components

Thank 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/37392



Pio

[Samogon]

Just bite the bullet and buy damn relay
 

[Samogon]

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.

[yo0]

Yes, waiting Monday to call keysight

[HighVoltage]

I took the relay of my 34410A apart
Here are the tear down pictures again, since we talk so much about this relay.

[yo0]

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.

ops! when you say corporate account do you mean ANY company? and no sells to individuals?

best regards

Pio

[Samogon]

Yes, no sales to individuals

[yo0]

Yes, no salas to individuals

thank you, i need to be creative when talk with them. 

best regards


Pio

[Samogon]

Not gonna fly
They will ask for payment method and delivery address to be a company

[yo0]

Not gonna fly
They will ask for payment method and delivery address to be a company

yes i know that, let see Monday

i´ll keep you informed


Pio

[yo0]

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 3540-05-91x

update: Feb 5, 2023,  unit still working fine! 

best regards


Pio

[pete99]

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
 

[HighVoltage]

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

Steve
I 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.

[pete99]

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

[HighVoltage]

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.

[pete99]

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