Products > Test Equipment

[SOLVED] 34401a - Cal Error 707

(1/6) > >>

Zucca:
It looks like there is nothing in the www regarding this error in the 34401a.

I just got an email from the laboratory I sent my 34401a (fresh from the used ebay market  ::), it passes the self test) for the calibration service.

Here the surprising new:


--- Quote ---S/N: US361229xx
Lab Notes: Unit was unable to pass or adjust on front zero offset and Ohm tests.  Cal Error 707.  Unit drifts when in Ohm function, suspect 400K resistor and 40K resistor are either bad or starting to go bad.   Agilent reports this issue in the service notes for these units.  Unit was unable to be adjusted and failed calibration.
--- End quote ---

Since the Lab. wants extra money to fix the device, I decided to fix the problem myself, so I did my homework and here what I found in the User Manual:


--- Quote ---707 Cal signal measurement out of range

The specified calibration value (CALibration:VALue) does not match
the signal applied to the multimeter.
--- End quote ---

In the service manual it doesn't say too much, but here the schematics (pag. 9-10) regarding the suspected two R (click on it for full resolution):



Now the good news is that I have 2 others working 34401a which I can use for reference.
The bad news is that I will start to work on it in May so this post right now is just to collect information regarding this issue and for building a reference for future similar cases.

Anyone out there who knows something more about this issue?

Ah, is the "front zero offset" related to the "Ohm tests" or should I expect more than a single problem to fix?
I don't know when but if it is possible I will fix this nice unit :box:!

Many thanks in advance,

Zucca:
Back in my home now, I will start soon to work on this. Here below the two pages calibration report from the lab. Looks like the 100 Ohm Range in the Ohm-meter function is not working properly (a offset is there of about 0.08 Ohm).

Regarding the failing zero offset calibration, I am not sure if those two resistors (400K resistor and 40K) can influence that too.




BTW, I understand the zero offset as the procedure to adjust the DMM in order to get 0 when 0 is applied in the input. Since I am pretty new in the calibration process then I´m trying to do little steps to make sure that I am not going in the wrong direction.

My big hope is to get some light in this dark tunnel when I open the unit and start metering the circuits up.

Keep you posted.

Dr. Frank:
The cal report may not give the correct hint.
In 1st instance it shows, that some cal values are out of range, and that's what to be expected if the unit has not been calibrated for a long time.

Well, if Ohm function has problems with zero Ohm calibration, that might be the well known problem with the input front / rear selector switch.
After years of usage (>10..20 yrs.), it will be dirty by out-gaseous of the plastic and debris, and some contacts will be hi ohm, so that you get unstable and nonsense reading in 2W Ohm, especially by zeroing.
And if the zero reading is unstable, you will get unstable full scale readings, also, which will in turn prohibit a stable cal reading.

As the lowest Ohm range is out of cal, but not the higher ranges, that gives the an indication that the problem is buried here.
You may post the 4W cal report, if available what's been wrong there.

Make a first test, simply measure a 2W short, in fixed 100 Ohm range, note the reading and switch to the rear panel, repeat the reading there, switch back to the front, and I bet the zero reading will be very different.
All may be in the dozen Ohm range, instead of < 0.1 Ohm

With that unstable switch, a calibration is not possible.

We had an elaborate thread here, what was the error, and how to solve that:

https://www.eevblog.com/forum/testgear/hpagilentkeysight-34401a-2w-problem/

Frank

Zucca:
Thanks Dr. Frank,

It makes very sense what you are telling me. Tonight I don´t have too much time to read the thread, but I promise I will.

Regarding this:


--- Quote from: Dr. Frank on April 28, 2014, 09:10:06 pm ---Make a first test, simply measure a 2W short, in fixed 100 Ohm range, note the reading and switch to the rear panel, repeat the reading there, switch back to the front, and I bet the zero reading will be very different.

--- End quote ---

I liked the proposal a lot, here the results with a short 2W@100 Ohm Range:

Front: 0.013 Ohm (it starts with 0.015 Ohm or 0.014 Ohm and then it settle down to 0.013 after about 10 sec.)
Rear:  0.005-0.006 Ohm with the last digit jumping between 6 and 5

Now same test with same cable in a second 34401a unit (fresh calibrated):

Front: 0.007-0.008 Ohm
Rear:  0.002-0.003 Ohm

and again in a third 34401a unit (fresh calibrated):

Front: 0.004-0.003 Ohm
Rear:  0.000-0.001 Ohm

Unfortunately I do not have the 4W cal report, when the lab saw something was wrong they interrupt the calibration process so all what I have are the above pages.

PS: I didn´t wait to warm up the three DMMs, so the temperature could also cause a drift in the values... Also I did not check if the setup configuration was the same in all the three units.

Zucca:

--- Quote from: Dr. Frank on April 28, 2014, 09:10:06 pm ---We had an elaborate thread here, what was the error, and how to solve that:

https://www.eevblog.com/forum/testgear/hpagilentkeysight-34401a-2w-problem/

--- End quote ---

Beautiful post, but it looks like none of my three 34401a has a (too) bad old front/rear switch.
Interesting enough I think I have the opposite case: 4W is not working but 2W is working.

Here my test setup:

The top one is the broken one, the other two are OK and fresh calibrated.
The middle one is used as a current meter, the other two R meter@100 Ohm fixed range.

Now this is the correct situation, using the bottom one in a 4W configuration:

5.5 Ohm as sensing current resistor and about 1 mA current to get the R value.

Let´s investigate the broken one, first in 2W:

looks good.

but in 4W:

:-DD

the funny thing is that sometime it drifts between 70 Ohm and 110 Ohm and then back to open circuit.

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod