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I did it ! I replaced the memory battery in my 3457A.
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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 :
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- 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?
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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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Show quoted text
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
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Hi Joel,
Since you're able to read out the contents of the RAM, would it be possible to write it to an EPROM and swap it?
I never use the save and recall commands... could this work or will it refuse to start up? Advantage would be to never bother with batteries again.
Just a firther thought, as I have the same DMM but did not yet even look inside :-/
cheers
Martin
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Show quoted text
On 30 Mar 2025, at 18:00, Joel Setton via groups.io <setton@...> 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?
<cardboard_shield.jpg> <All done.jpg>
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Hello Martin,
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The EPROM idea is interesting, I have explored it but I don't think it could work. The main issue is that the 8Kbyte RAM chip which holds the calibration data (TC5564APL-15) is also used to store the processor stack, firmware variables, user's memorized measurements etc.
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From the schematic, we know the RAM is used as follows :
- Calibration RAM data is from 0040 hex to 01FF hex with a special hardware mechanism to prevent accidental overwrite of this area.
- General storage RAM (processor stack, miscellaneous variables, user measurement FIFO etc) from 0200 to 1FFF.
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?.... In summary, replacing the RAM chip with an EPROM would not work. One (strong) reason is that the processor stack and RAM storage would not be writable.
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Cheers,
Joel?
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Hello Razvan,
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You are right, the original battery has 1 pin on the (-) end, and two pins on the (+) end. However, I found that the PC board has three plated holes on the (+) side including one in the middle, which makes it perfect for a standard battery holder with 2 wires. Please see the attached pictures.
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Have a great day !
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Joel
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"Joel Setton via groups.io" <setton@...> writes: Hello Martin,
The EPROM idea is interesting, I have explored it but I don't think it
could work. The main issue is that the 8Kbyte RAM
chip which holds the calibration data (TC5564APL-15) is also used to
store the processor stack, firmware variables,
user's memorized measurements etc.
From the schematic, we know the RAM is used as follows :
- Calibration RAM data is from 0040 hex to 01FF hex with a special
hardware mechanism to prevent accidental overwrite of
this area.
- General storage RAM (processor stack, miscellaneous variables, user
measurement FIFO etc) from 0200 to 1FFF.
.... In summary, replacing the RAM chip with an EPROM would not
work. One (strong) reason is that the processor stack
and RAM storage would not be writable. Using an FRAM might be a possible solution. A quick search showed that there's a FM1608B vom Cypress - 8Kx8 and available in DIP.
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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.
Another option is to ignore trying to save the calibration constants, replace the battery and send it to Keysight and let them calibrate it. Then it will be as good as you will get it. I did that, and they replaced the battery. There were before and after measurements - they made no attempt to save the constants. So everything was better after calibration. In contrast if you send it there are calibration constants about right, if it's in spec they will not adjust it. In contrast, by putting them all wrong, everything needs adjustment.?
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David,
everytime I walk past the delivery section in my company I wonder what "sending from and to" of these quite sensitive instruments will do to the calibration. There are always some instruments sitting on the shelfs waiting to be picked up for calibration. Naked, not packed in some special purpose container or such. If I was the instrument :-) I would prefer having me calibrated on-site, with nothing more than a trolley to be put upon and back in the rack when finished.
cheers
Martin
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My standard approach for replacement of batteries that support NVRAM containing instrument calibration , etc. is to connect either another battery or external power supply **with floating outputs** through a 1K ohm resistor to the PWB traces elsewhere on the board, usually after a reverse flow blocking diode in the battery circuit if it is present. Then removal of the old battery is easy without losing the contents of the RAM. The 1K resistor is just a precaution to keep from drawing high currents or other possible issues if you happen to connect to a wrong part of the circuit with the external power supply.
If one chooses to try the instrument power-up approach as you had mentioned make certain that you use a soldering iron that is not connected to third wire ground or has the tip grounded otherwise or else you will short out the battery and kill the RAM contents. Use of a battery powered soldering iron also allows safe removal of the battery. But that offers no help if a vacuum desoldering iron is required of which it frequently is.
Greg
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Hello Joel,
I was thinking it is the version with 4 holes. I found the same design
in 2 of my Meinberg GPS167 units. One had a battery holder with 2 pins
and one had a battery with 3 pins.
I looked around for 4 months for a battery holder for the BR2/3A or
CR1/2AA with 3 pins for my E4418B and found nothing. The Agilent EPM
series have the same battery type BR2/3A but the PCB only has 3 holes
exactly how the battery is. There is no 4th hole between the two (+) pins.
Can I ask which model of the battery holder you bought? Do you have a link?
Thanks for the pictures and details.
Best regards,
Razvan
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Show quoted text
On 31/03/2025 10:48, Joel Setton via groups.io wrote: Hello Razvan,
You are right, the original battery has 1 pin on the (-) end, and two
pins on the (+) end. However, I found that the PC board has three plated
holes on the (+) side including one in the middle, which makes it
perfect for a standard battery holder with 2 wires. Please see the
attached pictures.
Have a great day !
Joel
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Hello Dr. Kirkby, This would work in the case you can send it via some company. Keysight is not working with private persons anymore and I didn't find other labs that work with private persons at least in the EU. I tried to get some calibration services for a few power sensors and nobody wanted to work with me as a private person. Also, I tried to order from them the test leads for a multimeter and they requested a VAT ID and a company name. You don't have that you cannot order services or parts. Best regards, Razvan On 31/03/2025 13:18, Dr. David Kirkby, Kirkby Microwave Ltd via groups.io wrote: On Sun, 30 Mar 2025 at 17:00, Joel Setton via groups.io <
groups.io> <setton@... <mailto:[email protected]>> 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.
Another option is to ignore trying to save the calibration constants,
replace the battery and send it to Keysight and let them calibrate it.
Then it will be as good as you will get it. I did that, and they
replaced the battery. There were before and after measurements - they
made no attempt to save the constants. So everything was better after
calibration. In contrast if you send it there are calibration constants
about right, if it's in spec they will not adjust it. In contrast, by
putting them all wrong, everything needs adjustment.
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If one chooses to try the instrument power-up approach as you had mentioned make certain that you use a soldering iron that is not connected to third wire ground... Or the other way round? Put the instrument on an isolation transformer. cheers Martin
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Hi Razvan,
I used a Radiospares 185-4654 socket, which sells for one Euro or so. It turned out to be a no-brand Chinese import, you can find the same socket on Epay or other sellers. I could not find this type of socket from "premium" brands, like Keystone and others.
By the way, the same type of battery is sold as "ER14250" by some vendors, and is available from some vendors with leads and a 2-pin female connector. You may also want to investigate this type of solution.
Cheers,
Joel
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Hello David,
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What you are suggesting is obviously a good solution. However, it is WAAAAAY above what my "hobby budget" can afford. To make matters worse, Keysight will not do any business with private individuals, at least in Europe. You'd have to find and alternative calibration lab, which would calibrate the meter but would not probably not replace the battery since HP does not document this replacement.
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Cheers,
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Joel
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Hello Greg,
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I took the option of powering the 3457A in the normal way, with an earth connection as usual. At the same time I floated the soldering iron by powering it from a car battery and a DC-to-AC converter (the type which is commonly used in campers and similar vehicles). Another option is to use line power and an isolation transformer, if you have one. A portable, battery-powered or soldering iron would work just as well.
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Cheers,
Joel
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On 3/31/25 22:12, Martin via groups.io wrote: Or the other way round? Put the instrument on an isolation transformer. I've got nice isolation transformers for sale if anyone needs one. MGE Ultra Isolation 2.4 kVA and smaller.
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Thanks, I will order a few pieces to have them just in case.
Best regards,
Razvan
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Show quoted text
On 01/04/2025 12:01, Joel Setton via groups.io wrote: Hi Razvan,
I used a Radiospares 185-4654 socket, which sells for one Euro or so. It
turned out to be a no-brand Chinese import, you can find the same socket
on Epay or other sellers. I could not find this type of socket from
"premium" brands, like Keystone and others.
By the way, the same type of battery is sold as "ER14250" by some
vendors, and is available from some vendors with leads and a 2-pin
female connector. You may also want to investigate this type of solution.
Cheers,
Joel
|
Martin
Patricio A. Greco
Dr. David Kirkby, Kirkby Microwave Ltd