[volt-nuts] HP 3458A CMOS RAM

Rob Klein rob.klein at smalldesign.nl
Thu Aug 26 16:55:52 UTC 2010

  I've seen the subject of HP 4358 CMOS RAM come up umpteen times now.

Sadly, I do not own a 3458 myself and I do not know what exact type of
memory is used, but I've always wondered if it would be at all feasible to
use FRAM as a replacement. That would certainly put an end to all the
hassle and uncertainty of the battery back-up.

Just a thought.


Op 26-8-2010 17:25, Poul-Henning Kamp schreef:
> In message<949887D3866942A3857625622A0587AF at LapTop>, "Roy Phillips" writes:
> I found a HP3458A (on ebay for EUR1390) which had appearantly spent
> its entire life with a german manufacturer of electromechanical
> relays.
> The only problem were a dead bit in the GPIB port, and a fresh
> driver-chip solved that.
> To say the CMOS RAMS were old would qualify for understatement of
> the year award:  They were 5 year models (Suffix Y) datecoded in '89.
> I used the "MREAD" GPIB command to make a backup copy of the CALRAM
> chip to my computer, before unsoldering all three CMOSRams and
> mounting new ones (in sockets).
> Afterwards I checked the old CMOSRAM's battery state, by measuring
> the voltage over the GND and VCC pins in  10GOhm input mode and
> found a healty 2.9something volts.
> This is a point I think many of us overlook:
> If the meter has been turned on 24/7, the lithium cell does not do
> anything but sit there, and the reverse current of the diode that
> separates it from the chip is often enough to keep the battery in
> fine shape, despite the fact that it is not in any way shape or
> form intended to be rechargeable.
> And I think it is pretty safe bet that most HP3458A's are left powered
> 24/7, because that avoids the entire issue of warm-up etc.
> But yes, eventually you will run out of battery, but it was probably
> the easiest chip I have ever unsoldered: the holes were suprisingly
> large.
> So I would recommend you make a backup of the CALRAM with the MREAD
> command (I described how to in a post some time back) and let your
> batteries run out.
> If like me, you keep the meter powered, it may never happen.
> Poul-Henning


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