HP 34401a Self Test Fail

[lkmurdoch]

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,

Mike

[free_electron]

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?

Frank

[tszaboo]

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

[lkmurdoch]

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.

Michael

[tszaboo]

On the ohms, there are about a dozen transistor in a weird configuration. They are that way for protection. I would check if they are good.

[VK5RC]

Front -  rear different ,  2w 4w different?