[SOLVED] HP 34401a - Error 612, 613, 615, 617, 618, 619, 621

[ua4yhz]

The measurement of resistance and "cont)))" does not work. I checked your voltage map and all the voltages were approximately the same as yours. Those that are written in black squares.

When the inputs are disabled, the readings slowly show increasing resistance. The reading stops at about 800 ohms over the entire range of the resistance measurement.

[Dr. Frank]

The measurement of resistance and "cont)))" does not work. I checked your voltage map and all the voltages were approximately the same as yours. Those that are written in black squares.

When the inputs are disabled, the readings slowly show increasing resistance. The reading stops at about 800 ohms over the entire range of the resistance measurement.

The faulty values are inside the black squares, my correct ones are the hand written values. That's a first indicator that this OpAmp U201 is defect, again.

Maybe you can copy your own measurements inside this graph, also, but please apply a resistor and state, which measurement mode you're using.

I do not understand what you mean with  "inputs are disabled".
Are you using 4W Ohm mode and simply leave the jacks open??

Please make measurements only in proper configuration.   

Uh yes, and of course all this has nothing to do with U101, up to now.

Frank

[ua4yhz]

I just leave the nests open.
OK, thanks Frank.
I will look for the u102 chip and change it.

[Dr. Frank]

I just leave the nests open.
OK, thanks Frank.
I will look for the u102 chip and change it.

nests?
If you use 4W Ohm and let the jacks open, then the sense lines will simply drift to a random bias voltage, so that's no correct modus operandi.

Although U 201 (!) is a good guess,I would first make sure, that it really fails, by posting your voltages here.

Frank

[ua4yhz]

I just leave the nests open.
OK, thanks Frank.
I will look for the u102 chip and change it.

nests?
If you use 4W Ohm and let the jacks open, then the sense lines will simply drift to a random bias voltage, so that's no correct modus operandi.

Although U 201 (!) is a good guess,I would first make sure, that it really fails, by posting your voltages here.

Frank

I repaired the device today. Q201 and Q202 are broken. U201 does not seem to be working either. I will order these three items and then unsubscribe after replacing them.

[ua4yhz]

Today I changed Q201 (MMBF4392), Q202 ( MMBF5461) and U201 (AD706). Tests-pass. 2W mode worked. 4W mode worked.

[bitseeker]

Good progress.

[calin]

Well, i have to thank everyone  .. or brag about it
Thanks to this thread I revived my "gamble" 34401A that I scored on ebay for 180$ (shipped !!!)  . At arrival it was not looking very bad, power supplies all dandy but it was showing the usual errors 612, 613, 618 and 619.

After I replaced the famous U201 and Q201 bah still no luck .. same failures. I started to go component by component and after super careful inspection of the mainboard (under microscope) i found the culprit .. R122 which had left the magic smoke escape. Most likely it was fried by some voltage spike applied at input since that seems to be on the DCV measurement path if I read the schematic correct.
Anyways after that no more errors, all self tests pass  with success. I tested as much as i could and everything seems to be working correct as far as I can tell. It even looks like still being in calibration even if it seems that was last calibrated in 1995. I need to search for a cal lab to get it calibrated. I kind of remember that I saw somewhere on the forum someone saying that there is a cal lab in Phoenix, AZ (my town) which does not charges an arm and a leg for a calibration. Does anyone know the name of the company ? or find that post somewhere ?
Again, thanks all for the good info on this thread !!!

EDIT: I found them !!! https://4gte.com/products/75-calibration-special/
The thread is here - https://www.eevblog.com/forum/metrology/$75-calibration-with-adjust-and-data-for-a-variety-of-multimeterscountersetc/

[Dr. Frank]

Hello,

I bought this defect 34970A with the same error codes.
It has the same DMM circuit inside, like the 34401A, but on a separate board.
In the picture you see the infamous U201, AD706, which also was defective in my case.
The measurement on the constant current circuit revealed that the 2nd OpAmp, pin 5, 6, 7 broke down as usual.
I've written down the voltages before and after  '=>' repair .

What I was not aware of before is the fact that the bipolar input transistors break down in such a manner, that they source fault currents from the positive supply (+18V) into the +/- inputs.
The -input therefore drives an additional current via pin 40 backwards into the FET switches of ASIC U101, which raises the voltage on the Source of j-FET Q202 to these 12.6V.
One can measure this excess current of several mA by attaching a current meter in its mA range from the Source of Q202 (pin 1) to AGND, when selecting a low test current of 5µA or 500nA in the 1 or 10MOhm ranges.

After repair, the DAQ 34970A operates correctly again. It's from 2000, has still its first factory calibration (CAL COUNT = 32), and deviates by about +30ppm in all DCV and Ohm ranges, pretty good for that time period.
What's really nice, compared to the 34401A, that the Firmware features temperature measurement, and OFFSET COMPENSATION for the Ohm mode, which I'm missing on my old 34401A from 1993.

Frank

[bitseeker]

Thanks for including the analysis schematic, Frank. My 34970 just needs a new battery, but I'll know where to come back to if it misbehaves beyond that.

[Dr. Frank]

Thanks for including the analysis schematic, Frank. My 34970 just needs a new battery, but I'll know where to come back to if it misbehaves beyond that.

No problem.
Nobody asked about the T-sensor, so far.
Frank

[JohnAH]

Hello Gentlemen,
  Thank for all the great information about the Hp34401 errors 612, 613, 615, 617, 619 ect. But so far none of the solutions have solved my meter's failure.
Hoping you can help me or at least point me in the right direction. 

I have swapped out U201, q201, and q202. Looked for shorts and opens but have found nothing out of order. I have a good meter to compare it to but still can't seem to figure it out. Attached is Dr Frank's Current Source sheet with my values in blue. 

Thanks for any light you can shed on the problem.

John

[Dr. Frank]

Hello Gentlemen,
  Thank for all the great information about the Hp34401 errors 612, 613, 615, 617, 619 ect. But so far none of the solutions have solved my meter's failure.
Hoping you can help me or at least point me in the right direction. 

I have swapped out U201, q201, and q202. Looked for shorts and opens but have found nothing out of order. I have a good meter to compare it to but still can't seem to figure it out. Attached is Dr Frank's Current Source sheet with my values in blue. 

Thanks for any light you can shed on the problem.

John

John, your voltages are partly ok, if you compare it with the latest diagram I have published for my 34970A. The slight differences probably occur due to different supply voltages and a different zener diode.
It's not clear, what mode you use, and in which state you took the measurements.. i.e. open circuit in Ohm modes, or 4W, or which resistor was attached?

Which error messages do you get, when you are doing the full self test?

Please measure the constant current values e.g. in 4W mode out of the "Input Hi / Lo" jacks, for 100 Ohm to 10MOhm ranges.

Frank

[JohnAH]

Error codes 612, 613, 615, 617, and 619
blue ink measurements were 2 wire ohms auto

4 wire in respective ranges against high accuracy resisters .1%
R            I             Range
100ohm .998mA    100 range
1k ohm  .998mA    1K range
1k         .o991 mA  10k range
1k         .0096 mA  100k range
80k       .0095mA   1M range
80k       .0046mA   10M range

The ohm readings were quite close. I didn't calculate them out but all probably within 1%.

[Dr. Frank]

Error codes 612, 613, 615, 617, and 619
blue ink measurements were 2 wire ohms auto

4 wire in respective ranges against high accuracy resisters .1%
R            I             Range
100ohm .998mA    100 range
1k ohm  .998mA    1K range
1k         .o991 mA  10k range
1k         .0096 mA  100k range
80k       .0095mA   1M range
80k       .0046mA   10M range

The ohm readings were quite close. I didn't calculate them out but all probably within 1%.

1M and 10M ranges have the wrong currents, if you didn't mix up the ranges / measurements.. should be 5µA and 500nA instead of 10µA and 5 µA.. a pity that you can't measure the low currents with higher resolution.
Anyhow, this would partly explain errors 612, 613 but not the others, as these currents or compliance voltages seem to be ok.

Another question:
What have you done with Q201, Q202, U201:
Did you swap  them, i.e. really swap Q201 and Q202,  or have you replaced all 3 components with new, compatible ones?

Would it be possible for you to check all these ranges at near Full Scale, i.e with the appropriate resistors, like 10k, 100k, 1M and 10M?

Did your instrument fail, or have you bought it as defect?

The current sources seem to be work, maybe partly, but something is wrong at the output stage Q202 and behind.
Maybe the switches inside the ASIC are steered incorrectly...
I have to think a bit more, in the meantime.

Frank

[JohnAH]

yes, i just checked, i mixed them up
R            I             Range
100ohm .998mA    100 range
1k ohm  .998mA    1K range
1k         .o991 mA  10k range
1k         .0094 mA  100k range
80k       .0043mA   1M range
80k       .00012mA   10M range

u201 was new. QS

[Dr. Frank]

All right, now the 500nA seems NOK, but already the 5µA might be just an error from your other DMM, due to lack of resolution. What other DMMs do you have?
Please try to measure with an appropriate  1% shunt, to decide, whether the sources are ok, or not.
What about Q201, 202? Have you changed anything with them?
Or what's the meaning of to "swap out"?

In which range and mode did you measure the voltages in your diagram?
Open jacks, or something connected?

[JohnAH]

Sorry it looks like half the message I sent last was truncated.

We don't have any better DMMs.
both Qs were known good used stock. They were not swapped with each other.

The diagram was 2 wire auto range, open jacks. 
I can probably get high ohm precision resistors but it going to take a little time.

The meter has been working for a long time. It died when a customer borrowed it. It is being used to verify accuracy in a ICT machine via IEEE program.
 

[Dr. Frank]

OK, under these circumstances, at first please measure the voltages with a load connected, e.g. 1k resistor in 1k range.

I assume, that U201, Q201, Q202 are fine, as the currents might work ok, as far as one can tell from your measurements.
If you have a 2nd 34401A, then you might measure the 80k resistor precisely, use it as a shunt, and measure 10µA and 500nA, using the 2nd DMM in its 1V and 100mV range, i.e. about 800mV @ 10µA and 40mV @ 500nA, but with much higher resolution. Simply use a calculator, and set the 34401A to R > 10¹⁰ Ohm. The absolute accuracy is not important, 1% is fine, but I just want to get rid of offsets and alike.

I assume that the transistor array might be damaged, or the 3rd FET which goes to GND.

Didn't we have that here, recently?

Sorry, need to sleep a bit now, continuation by tomorrow.
Frank

[Dr. Frank]

Another idea: Please check if a 10V dc signal is read correctly in the 100V range, compared to the 10V range. maybe the relay is damaged, as it's used also for all these failing tests.


I assume, that the Ohm circuit was not damaged at all, initially (have you checked the correct function before you changed the components?).

Only the 5 tests for current source compliance failed, but that could also be caused by components in a completely different section, like this relay, or other components inside the DCV path.
Therefore please check all DCV ranges also.

Frank 

[JohnAH]

That might be it. The 10V scale is slowly to rises to 9V. It really never gets there.
The 100V scale measures 10V.

Using Fluke Calibrator.

[JohnAH]

Got it! C

[Dr. Frank]

Got the fault?

[JohnAH]

I don't know what is going on with my posts but a lot of them are getting truncated.

Yes found it. R105 had a cracked solder joint. It is passing everything now.

Thank you Dr Frank.

[shaohu.tang]

In a few days I will also plan to repair a few of them, and then release them to ask everyone!