Hello,
I just want to give notice, that I also have replaced successfully those
3 NVRAMs in my HP3458A from 2000.
The cal data had been saved by the MREAD command (thank you again,
Poul-Henning).
Both 32k*8 and the CalRam DS1220Y with date code 9935 were still alive,
but it was not possible to measure the internal battery voltage over the
protection diode reverse current.
A fellow volt-nut (not active here on this list) programmed the fresh
DS1220AD for me.
He owns an HP3458A from 1989, which had 2 exhausted 32k*8 DS1235Y, but
the Cal Ram, DC 8840 (!) was still ok.
In 2009, I had lowered the LTZ1000A temperature in my 3458A to about
55°C, for a quasi opt. 02.
The long term monitoring of the 3458A against a Fluke 5442A and two
other LTZ1000 references (@ 7,147V, running 24/7) still shows, that the
whole group of 4 references agree within +/-1.5ppm after that 4 years
period.
The recent comparison to the (obviously freshly calibrated) gear of my
fellow volt-nut agreed within < 1ppm.
So, my 3458A (opt. 01+02) should be healthy for the next 15 years.
Frank
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