[volt-nuts] HP 3458A CMOS RAM

Robert Atkinson robert8rpi at yahoo.co.uk
Thu Aug 26 18:41:05 UTC 2010

I also don't have a 3458A, but I do have experience with early battery backed up CMOS RAM. FRAM is an option. Can someone tell me the part number of the CMOS units currently used and I'll do a comparison. An other option that I've used before is external (to the module) back-up. Add a schoktty diode in series with the Vdd and use an external lithium (with an other diode) or rechargeable too keep the module powered. Or you can carry out surgery on the module and replace the cell. This problem is also common on video games and Sun SparcStations. See http://www.jmargolin.com/rdy2k/hdzram.htm and http://cmheong.tripod.com/work/mk48t02.html
Robert G8RPI

--- On Thu, 26/8/10, Rob Klein <rob.klein at smalldesign.nl> wrote:

From: Rob Klein <rob.klein at smalldesign.nl>
Subject: [volt-nuts] HP 3458A CMOS RAM
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Date: Thursday, 26 August, 2010, 17:55

  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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