Hello Joel,
Thanks for sharing your repair. I have a question related to the battery
holder.
Your original BR2/3A battery had 3 pins if I am not mistaken. One on one
side and two on the other side.
Did you find a socket that also has 3 pins and matches the holes on the
PCB but takes 1/2AA battery ?
Thanks,
Razvan
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On 30/03/2025 18:00, Joel Setton via groups.io wrote:
I did it ! I replaced the memory battery in my 3457A.
My used 3457A was built in the late '80s and still had its original
lithium battery, with a 1989 date code on it. This battery obviously
needed replacement.
Unfortunately, the battery is soldered to the processor PC board and
provides permanent Vcc for a low-power CMOS SRAM chip which holds the
multimeter's calibration constants. In other words, interrupting the
SRAM supply would result in the loss of calibration data.
Thus, the battery must be replaced while the 3457A is powered up. This
is a bit of a nail-biting experience, but it can be done. One useful
trick I used is to prepare a cardboard shield which covers the CPU board
and protects it from any solder drops and shorts, while allowing access
to the battery. And of course the soldering iron must be floating.
Replacement batteries in the original size (lithium BR 2/3AA with solder
pins) are still available for a few dollars, but I chose to install a
slightly different battery, a Tadiran SL750 which has a 1/2 AA size, for
which sockets are available. Using a socket means that in 10 years, the
next battery replacement will be easier : with the multimeter powered
up, just pop out the old battery and insert a new one. Another advantage
is that 1/2 AA lithium batteries are very easy to find, there's a good
chance that your local supermarket has them.
Now I'd like to share some thoughts and questions about this battery. As
we all know, lithium batteries have a long, but finite life. Even though
the current drain on the battery is less than 0.2 uA at room
temperature, at some point in time the battery will die.
I read the 3457A user and service manuals, but I couldn't find a single
mention of the battery. Nothing about battery life, no instructions on
how to replace it, even nothing that says "contact your nearest HP sales
office". To me, this doesn't make sense, especially when considering
that this multimeter was introduced in 1986, at the time of the "old HP"
which produced high-quality instruments, not expendable stuff. I could
only think of a few possibilities :
- Maybe the engineers at that time believed that lithium batteries could
last forever ;
- Or they thought the multimeter would be scrapped when the battery runs
out, or before it does ;
- Or they decided that if a multimeter loses its calibration data
because of a dead battery, it should be returned to HP for battery or
processor board replacement followed by re-calibration. That's an
expensive proposition.
None of these options make any sense to me in the context of the "old HP".
Further thoughts and comments will be most welcome !
Joel
