Electronics > Repair
Agilent 34401A Bubble on PCB ... can it be saved ? (SOLVED)
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Kleinstein:
The 10 K range looks like it works. To check if the sum really works Ok one would need to measure both resistors separately to really add the numbers. The expected difference that may show up would be in the 6 th maybe 5 th digit.

For the problem with the low current one would need to do the similar test with larger resistors, like 4.7 M or a chain of 6-8 x 1 M. The 10 M range where a larger error is expected.
The_Spectrum.A_idiot:

--- Quote from: Kleinstein on September 20, 2024, 09:11:44 pm ---The 10 K range looks like it works. To check if the sum really works Ok one would need to measure both resistors separately to really add the numbers. The expected difference that may show up would be in the 6 th maybe 5 th digit.

For the problem with the low current one would need to do the similar test with larger resistors, like 4.7 M or a chain of 6-8 x 1 M. The 10 M range where a larger error is expected.

--- End quote ---

Okay lets say hypothetically , all these tests show that we are kind of working, in certain / most ranges.

is there a chance to even calibrate and keep the instrument error free ? or this is just a sanity check to make sure that we are measuring true regardless if the instrument is not passing it's self tests ?

Do you think was a mistake that I've changed every components all at once ? and most probably some components are not "matched" per say ?

Just so that I would know IF i have to live with it or hope for a trustful future

Because is all about trust. If I can't trust it , I can't use it.
coromonadalix:
that's why you use the meter self tests. if it fail you have a problem

and when you don't get any fails, the ultimate answer reside in dmm calibration,  and you'll know it is perfect

But i'm not sure how the self test may handle bad calibration, or out of calibration ??

and just a comment, for future(s) purchase(s) if any,    always ask to see an passed self test picture, or ask the seller to do it
The_Spectrum.A_idiot:

--- Quote from: coromonadalix on September 20, 2024, 09:39:31 pm ---that's why you use the meter self tests. if it fail you have a problem

and when you don't get any fails, the ultimate answer reside in dmm calibration,  and you'll know it is perfect

and just a comment, for future(s) purchase(s) if any,    always ask to see an passed self test picture, or ask the seller to do it

--- End quote ---

I agree. It was a kind of deceptive practice as he listed it as {tested good} and at the very bottom of the description, 'continuity and resistance not operable' ... and you guest it I found out to read the fine print before looking as good deal.

On his defence it was mentioned. I didn't read it.

Anyway lesson learned. Now back to trying to get this **** working.

I would like to thank everyone for their help and input I very much appreciate it !!

Regarding bad calibrations well I've changed components that were supposed to be paired and verified with other non paired but original close enough components.

whether or not a proper full calibration will make/force the meter to pass it's self tests as at the moment in essence I don't have any faulty components that I hope someone will let us know.
Kleinstein:
The parts that were replaced don't need to be paired and most of them should not even effect the calibration / scale factors. From the changed parts it is only the offset of the OP-amp that has a small effect on the scale factor of all resistance ranges. The OP-amp bias and leakage currents can also effect the high resistance ranges (10 M + 100 M and a little 1 M) . The others should not be effected enough to get much of an error.

It looks like the PCB is not yet fully clean / dry. If there is some conductive flux residue or similar it can take quite some cleaning to get rid of the leakage.
Worst case there is leakage from the overheated PCB part or dirt inside the bubble.
one may have to close the case for the tests, so that light would not effect some of the SMD parts - some can be a bit light sensitive.

Changing all the parts was not such a bad idea. The OP-amp was very likely bad from the tests and the other parts are not that expensive and possibly damaged.


The voltage and current ranges should not be effected by the repair, unless there is PCB contamination.
There are a few additional tests that one can do with relatively little effort / instruments to check a few more points no checked so much in the self test.
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