Electronics > Repair
[SOLVED] HP 34401a - Error 612, 613, 615, 617, 618, 619, 621
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abnormalalien:
Took some time to get the AD706s from Newark but I finally replaced both U201 and U400 and now the multimeter passes all self-tests. I also tested various functionality: DCV, ACV, and 2WR are all great. Tested 4WR with a handful of resistors and found that the values seem reasonable. The only oddity is that when nothing is connected to the inputs and 4WR is selected, it does not read Overload. I believe it should read OL when there's no inputs right? Is that a sign of another problem?

Haven't tested ACV yet (too many researchers not enough machines) or ACI (how does one even go about sourcing ACI?).

Thanks again for all your help!
Zucca:
BOOM, Enjoy your repaired meter.

What does it read then in 4W with nothing connected? Remember the floating Voltage on Sense + and sense - is interpreted by the DMM as a resistance value.
I'm out from my lab so I can not check, but to me it's not a problem.

Now you should calibrate that puppy, self test passed doesn't mean it will works 100% right.

In USA a 34401a can be calibrated for cheap, do it.
abnormalalien:
When I first turned it to 4wire, it was around 0.2Mohm but it looked like it was climbing. Now, it seems to be varying between 0.37Mohm and 0.38Mohm. You mean it is better to pay to get it calibrated rather than do it myself?
bitseeker:
abnormalalien, any stray voltage on the sense inputs will register as a resistance value. Remember that the DMM sends current through the device under test, measures the voltage across it, and then calculates the resistance. Rub your finger across the input jacks while in 4W mode and you may be able to alter the apparent resistance that the meter sees.

On my 34401A in 4W mode, sometimes it goes up to around 0.3M and stays for a while or goes down to zero. However, even if it goes up for a while, it eventually ends up at or near zero. Switching to other modes and returning will display a resistance for a little bit and then returns to zero.

It's best to check that it's zero with a 4-wire short and measures known resistors correctly.
Zucca:
Thanks bitseeker, that's what I was thinking.


--- Quote from: abnormalalien on July 11, 2018, 09:45:07 pm ---You mean it is better to pay to get it calibrated rather than do it myself?

--- End quote ---

If you have some calibrators and you trust them, well good luck.
I will put 75$ now 99$ on the table and considered it done, no brainer:
https://www.eevblog.com/forum/metrology/$75-calibration-with-adjust-and-data-for-a-variety-of-multimeterscountersetc/
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