Another 3458A on board

[chris_11]

Helll,

hope that I can hijack this thread. otherwise I will open a new one.
Got an used HP3458A yesterday. Serial is 2832A04913. CAL all and ACAL all work. However the strange thing is, that the DCV reads about 0.15% too high. Which is way out of spec. With the assumption that somebody had played with the CAL I did put in a CAL value with some agreement with my Keysight 34461.
Measuring a 9V battery has even on NPL10 only the last digit move by one digit. You can literally see the battery discharge over the combined input resistances. With a ACAL All now the DCA range looks reasonable. However I have no experience if the reference or any other thing is still faulty. So any advice will help.
Before I take it to the cal lab I like to make sure that nothing is broken. For that I am willing to build some LTZ1000 boxes if someone can direct me, where to buy the precision wire wound resistors needed.

Thanks in advance
Christian

[plesa]

Helll,

hope that I can hijack this thread. otherwise I will open a new one.
Got an used HP3458A yesterday. Serial is 2832A04913. CAL all and ACAL all work. However the strange thing is, that the DCV reads about 0.15% too high. Which is way out of spec. With the assumption that somebody had played with the CAL I did put in a CAL value with some agreement with my Keysight 34461.
Measuring a 9V battery has even on NPL10 only the last digit move by one digit. You can literally see the battery discharge over the combined input resistances. With a ACAL All now the DCA range looks reasonable. However I have no experience if the reference or any other thing is still faulty. So any advice will help.
Before I take it to the cal lab I like to make sure that nothing is broken. For that I am willing to build some LTZ1000 boxes if someone can direct me, where to buy the precision wire wound resistors needed.

Thanks in advance
Christian

What is last calibration date? What is self test result? Try to log the cal values over time
https://xdevs.com/doc/HP_Agilent_Keysight/3458A/service/3458A-18A.pdf
If you have GPIB adapter try to log the cal values by Python script
https://www.eevblog.com/forum/metrology/raspberry-pi23-logging-platform-for-voltnuts

[chris_11]

Last cal was by Fluke in 2012. However the cal seal on the side screws are broken so anything could have been swapped. Self test does pass. Have it now on for the next days and will Autocal it at least daily to get drift data. The VFD seem to be quite (too) good for such an old instrument. There is an older Agilent cal sticker from 2009 on the rear.

Christian

[TiN]

I agree on plesa's sugesstion. Test per SN18 procedure for stability , and also run meter at NPLC100 24/7 (DCV 10V range) to make sure ADC works well. Some more detail and example test result can be find here.

[TheSteve]

I would also open it up and check the date on the nvrams. If they are old you'd certainly want to replace them before having it calibrated.

[TiN]

Good idea too, I didn't mention NVRAMs because that's obvious and has to be done regardless of the chip dates.
4913 S/N unit is around 1990-1991, so it's already ancient, however I'd expect Fluke replace NVRAMs if it was serviced by them in 2012.

[chris_11]

Hello,

today I opened up my Metuselah. Those unit was last calibrated by Agilent in April 2011 and  later Fluke in March 2012. Self test passes as well as ACAL all.
CAL?72 over two days was 0.25ppm max between three ACAL ALL.
Reference board is the original with LT1013 date code 8851 which is week 51 in 1988, so that matched with the vintage of the serial. The  topside analog board where the reference is plugged on reads mostly 1990 date codes, so that will be the original too. The processor board with the Dallas NV RAMS seems to be a bit younger It still Rev A with  09-9217 USA Made and has two Dallas NVRAMs date code 0640C   below the EPROMS but has still one Dallas NVRam date code 9814D.
So the 9814D seems to be the most scary one which is the closest to the rear side.

The calibration seals on the handle screw from Agilent and Fluke were broken so there could be some change after 2012.

How can I upload pictures I have some from the unit?

Christian

[chris_11]

Here some pictures:

[Dr. Frank]

Hello,

..

CAL?72 over two days was 0.25ppm max between three ACAL ALL.
..
The processor board with the Dallas NV RAMS seems to be a bit younger It still Rev A with  09-9217 USA Made and has two Dallas NVRAMs date code 0640C   below the EPROMS but has still one Dallas NVRam date code 9814D.
So the 9814D seems to be the most scary one which is the closest to the rear side.

The calibration seals on the handle screw from Agilent and Fluke were broken so there could be some change after 2012.

How can I upload pictures I have some from the unit?

Christian

Hello Christian,

the oldest nvRAM, date code from 1998, labeled DS1220, is the calibration RAM, and really is the crucial one.
You should at once read its content into a file on your PC, and later program all these calibration constants in a replacement chip.

The other two nvRAMs DS1230 are not critical, but should be replaced also, as they are already 11 years old.

Your A/D hybrid seems to be healthy.


Frank

[rastro]

Christian,

The instrument looks in excellent shape physically.  Great find!   

[chris_11]

The NVRAMs and Eproms are now new. The Eproms used are Atmel AT27C512R-45PU  (45ns) which seem to run fine.
What is a bit strange is that the readable string in the CAL RAM around 000005D0 reads like  2823A08118 which would be a later unit than my serial 04913. My assumption is, it is strange that Agilent in 2009 and Fluke in 2012 calibrated this unit with a 9814 CAL-RAM which the unit had when I bought it. That is an explanation too why the calibration was way off.

Christian