Another 34401A Repair Question

[smgvbest]

Hi I got a deal on eBay (of course) for an as-is 34401A.
After getting down on my test bench I cleared the previous messages and ran a full self test which is passed.
Ok so good.  surprised but good.    Next I started testing it out and on DCV the 0-10V ranges are off by as much as 700mv
but greater than 10V (up 30v far as my power supply will go) is't dead on. 
I'm thinking maybe a failed Cal?   but could be a real problem
Is it possible to calibrate only the 0-10V ranges or do you have to cal the entire unit?

[ManateeMafia]

Could be a failed cal. Have you tried shorting the inputs on all DCV ranges? They should read close to zero. The calibration manual lists the specs in Chapter 4.

The 10V range has the offset cal (shorted input) and gain cal (10V). There is also a -10V cal that is recommended after a/d servicing or replacement of cal ram. Perhaps the cal ram has a problem? I think there have been a few members with the bad U505.

I can't tell you about doing individual ranges but you can probably find an answer in one of the several 34401A repair threads.

[deadlylover]

You can adjust the individual gain ranges no problem, except the zero offset adjustment, which will do it for all ranges automatically.

[Dr. Frank]

Yes, I also can confirm, that the different ranges of the 34401A can independently be calibrated, regarding gain factors.

Anyhow, the -10V calibration affects linearity for all ranges.

Linearity and polarity inversion should be checked before attempting to re-calibrate the instrument, especially the -10V item; afaik, this is required only after A/D replacement, and should not be done routinely.

Frank

[KSP]

I can also confirm that you can calibrate individual ranges at full scale. As stated before, the zero cal will automatically run for all ranges. Just apply a good 10V source, set cal range to 10V and press enter. Manuals are available on the Keysight website if you need more info, but getting to the cal menu is simple enough

[smgvbest]

Thank you all for the replies.  I'll do the zero cal then the gain for up to 10V and see if that resolves the issue.
now to go re-read the procedure on how to cal it.

[smgvbest]

Just wanted to give an update
I've done a zero cal and the DCV from 100mV to 10V front and rear and those ranges are now atleast as accurate as my DM3068.
No cal errors and its been working well since.   I was unable to do a cal on the DCI as it looked like I missed the fact there is no 3amp fuse in the rear holder.  as well as no fuse cap that should be there.   so will need to order from keysight.

[ManateeMafia]

  Good to see you got it fixed.

[siggi]

I was unable to do a cal on the DCI as it looked like I missed the fact there is no 3amp fuse in the rear holder.  as well as no fuse cap that should be there.   so will need to order from keysight.

I got a replacement from Digikey, see this thread for the part numbers that fit: https://www.eevblog.com/forum/index.php?topic=49877



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[smgvbest]

Thank you
I already order from keysight,  had no trouble actually it's part number 2110-0869 @ 14.79.   I had a few other cosmetic things I wanted to order so worked out with keysight,  free express shipping over $50 which I had.