Author Topic: Agilent 34401A 2w drift and high readings when power up  (Read 6491 times)

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Online yo0

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Agilent 34401A 2w drift and high readings when power up
« on: June 20, 2017, 04:00:14 pm »
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
« Last Edit: June 22, 2017, 05:14:13 pm by yo0 »
 

Offline mzacharias

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #1 on: June 20, 2017, 04:45:33 pm »
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.
« Last Edit: June 20, 2017, 04:47:14 pm by mzacharias »
 

Online yo0

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #2 on: June 20, 2017, 04:55:22 pm »
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

« Last Edit: June 20, 2017, 05:08:28 pm by yo0 »
 

Offline HighVoltage

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #3 on: June 20, 2017, 08:58:36 pm »
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

There are 3 kinds of people in this world, those who can count and those who can not.
 

Online yo0

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #4 on: June 20, 2017, 10:25:07 pm »
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
« Last Edit: June 22, 2017, 05:11:13 pm by yo0 »
 

Online yo0

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #5 on: June 21, 2017, 06:53:58 pm »
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
« Last Edit: June 21, 2017, 07:29:05 pm by yo0 »
 

Offline HighVoltage

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #6 on: June 21, 2017, 09:21:32 pm »
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.

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Online yo0

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #7 on: June 21, 2017, 10:24:17 pm »
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
« Last Edit: June 21, 2017, 10:34:55 pm by yo0 »
 

Offline carl_lab

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #8 on: June 22, 2017, 09:43:50 am »
...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.
 

Offline HighVoltage

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #9 on: June 22, 2017, 11:38:33 am »
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.



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Online yo0

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #10 on: June 22, 2017, 01:26:15 pm »
Thank you, what are the simptoms lead you to identify the relay as bad?


Best regards.


Pio
 

Offline HighVoltage

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #11 on: June 22, 2017, 02:48:00 pm »
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.
There are 3 kinds of people in this world, those who can count and those who can not.
 

Online yo0

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #12 on: June 23, 2017, 03:04:17 am »
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
« Last Edit: June 23, 2017, 04:35:44 am by yo0 »
 

Offline carl_lab

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #13 on: June 23, 2017, 05:34:32 am »
... 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?
« Last Edit: June 23, 2017, 05:36:08 am by carl_lab »
 

Online yo0

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #14 on: June 23, 2017, 05:48:14 am »
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
« Last Edit: June 23, 2017, 05:50:59 am by yo0 »
 

Offline floobydust

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #15 on: June 23, 2017, 06:01:14 am »
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.
 

Online yo0

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #16 on: June 23, 2017, 02:30:32 pm »
And at this morning this is the reading at start up



Best regards


Pio
« Last Edit: June 23, 2017, 02:44:26 pm by yo0 »
 

Offline HighVoltage

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #17 on: June 23, 2017, 05:08:07 pm »
It looks like you definitely need a new relay.
There are 3 kinds of people in this world, those who can count and those who can not.
 

Online yo0

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #18 on: June 23, 2017, 05:40:25 pm »
It looks like you definitely need a new relay.

i think so, Key$ight is waiting for me  :palm:


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
« Last Edit: June 23, 2017, 06:18:21 pm by yo0 »
 

Offline carl_lab

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #19 on: June 23, 2017, 07:40:00 pm »
And at this morning this is the reading at start up
Batteries of your Fluke handheld are OK?  ;)
 

Online yo0

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #20 on: June 23, 2017, 07:45:45 pm »
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
 

Online yo0

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #21 on: June 24, 2017, 12:16:41 am »
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
« Last Edit: June 24, 2017, 12:23:30 am by yo0 »
 

Offline Samogon

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #22 on: June 24, 2017, 04:43:23 am »
It looks like you definitely need a new relay.

i think so, Key$ight is waiting for me  :palm:


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
 

Online yo0

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #23 on: June 24, 2017, 05:30:03 am »
It looks like you definitely need a new relay.

i think so, Key$ight is waiting for me  :palm:


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
« Last Edit: June 24, 2017, 05:34:21 am by yo0 »
 

Offline Samogon

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Re: Agilent 34401A 2w drift and high readings when power up
« Reply #24 on: June 24, 2017, 12:41:32 pm »
Just bite the bullet and buy damn relay :)
 :horse:
 


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