3421A CAL RAM

[Dave Frederickson]

(03-30-2017 09:14 AM)Hans Brueggemann Wrote:  currently away from my 3468 and also not in possession of a 3421, but CAL ram error most likely points to a flat CAL ram battery (at least true for 3468), and therefore, it's very likely that the CAL data are already lost. You may want to check that first. you may want to post your question in the eevblog forum's repair section. The folks over there are toying with all kinds of vintage equipment and have already helped me out many times. They can probably provide you with the proper command sequence and a set of CAL data for your 3421. That won't bring back your instrument to factory accuracy level, but would at least allow you to exercise it, before you are doing a full cal & adjustment.

Yes, the battery was dead and has been replaced on both of my 3421A's along with the 6V SLA battery. I procrastinated and did not order another battery for my 3468 and now it has a CAL RAM checksum error, too. The solution to clearing the error is to perform a complete calibration, that is, write new calibration factors to the CAL RAM. Problem is I don't have the calibration standards necessary. However, nearly half of the steps in the calibration procedure can be performed using a shorting plug.

The other way to write new parameters to the CAL RAM would be to use this undocumented CAL command. I have a pretty good idea of the default parameters.

Excellent idea to consult eevblog. That is where I got the information on replacing the battery, from an HP 3457A post. BTW, the replacement battery for the 3421A and 3468 is a 2/3A 3V lithium, available from Digi-key.
http://www.digikey.com/product-detail/en...6-ND/61161

Dave