Electronics > Repair

HP 34401a Self Test Fail

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Hi everyone,

My first post so here goes.....

I have a HP 34401a that fails self test. It does measure AC volts, DC volts reasonably accurately (very close to a Fluke 45) but Ohms is way off cal.

The Ohms function measure 00.000 when the leads are shorted, but nothing else. I have checked for signs of obvious damage internally and checked the

power supply voltages which are fine. Any suggestions gentlemen?

Thanks in advance,


error code ?

Dr. Frank:
Hi and welcome..

not possible to figure out. I suggest you give more detailed hints:

- do you run the self test, and then you get an error?
- error code available?
- what does the instrument read in the different Ohm ranges, each 2W and 4W, with shorted leads and with resistors of appropriate value attached?
- did you check the same on the rear connectors?


Download service manual from Agilent. Check for your error code in that.

Hello all,

No error code was displayed after the self test.

I checked the Ohms current source opamp (U201) for correct supply and reference voltages and they are correct.

Interestingly on a whim I checked for a voltage on the test leads of any kind and the is none.....the Fluke 45 on the bench shows 1.56 volts DC.

Therefore I suspect that there is indeed an issue with the Ohms current source.

I would appreciate any insights any of you my have to offer.



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