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Hello,

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I have a very nice 3457A which has a 40-year old battery. New batteries are quite inexpensive and easy to find, but I'm quite scared at the prospect of replacing the battery without first dumping the calibration data to a file, and having a way of reloading it if anything goes wrong during the replacement process. Someone already tackled the problem of storing the cal data on a PC () but I couldn't find anything about how to restore the data from the PC to the 3457A if the data is lost.

Right now my 3457A is sitting there with a battery which is 40 years old, and counting ...

Any help or pointer(s) would be sincerely appreciated !

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Joel

Apparently there are security countermeasures in place to prevent the cal data being written back in via GPIB (Understandable for this sort of equipment, can't have bad actors poking around ruining critical measurements...), so for now the only way to restore the cal data is to write to the NVRAM chip directly in a chip reader.

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My skills are very much not in decompiling firmware, so I'm of no help, but if anyone out there were to figure out how to restore the cal data via GPIB, a lot of us would be quite happy...

I wonder if there are some secret commands, or if the replacement of an NVRAM by Keysight is always followed by a full calibration anyway, making the whole thing moot for them?

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Jared

Hi Jared,

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Thanks for your inputs. The 3457A doesn't use an NVRAM chip (as other HP instruments do), it uses a low-power CMOS static RAM with a permanent supply provided by a lithium battery. The problem is that the battery has a finite life, and its replacement is made difficult by the fact that it is soldered to the PCB and doesn't have a socket. After a few decades, the battery must be replaced while maintaining an uninterrupted supply to the SRAM.

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Of course, performing this replacement without interrupting the SRAM supply is tricky and carries some risk of losing the calibration data in the SRAM. Getting some protection from this risk was the reason behind my question to this group. Apparently, dumping the precious calibration data from the SRAM to a PC file can be done, but I couldn't find any information on how to reload the data from the PC to the 3457's SRAM if the data is lost. I'm sure there must be a way of doing this via the HP-IB, since this is the way HP performed the full calibration in manufacturing. This would be via a set of special HP-IB commands, which are likely to be documented in the calibration software which HP made available at the time the 3457A was manufactured, but which I couldn't find.

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There could be similar HP-IB commands for other DVMs, for example the 3478A or the 3458A. These commands would enable a successful reload of the calibration data from a PC file to the SRAM.

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Thanks again,

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Joel

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