OT: Can CMOS battery on PC motherboard be hot-swapped?

Folks,

Got a Dell Vostro 200 mini tower with XP on there that seems to be a bit
off in the realtime clock lately. Around five years old so needs a new
3V coin cell on the mobo.

In order not to lose all the setup stuff, can those CR2032 coin cells be
hot-swapped while the PC is running?

Of course using ESD straps, being careful and all that.

 

the BIOS flash update utility has a backup feature which keeps settings
as well.
you back it up, swap the battery, and then re-apply the backed up flash
image.

And yes, you CAN apply an external 3V source to the MOBO. Just
remember that you will be fighting the very low internal resistance of a
dead battery for the few seconds you are under power as you remove it,
and for the few seconds you re under external power as you install the
new one.

Be very careful about polarity, and do not exceed 3 volts so you do not
begin "feeding" the battery.

As a side note, many modern motherboards have enough capacitance at
that sub-circuit location to retain things long enough for you to swap
the battery. I do not know if yours is such a design.

another side note is that RTCs in PCs are not very accurate with the
original Pc deign and crystal. Newwer designs may use more accurate
clock sources, but most do not, and your most accurate clock possible is
your cell phone, or iPad or other cell system connected or GPS enabled
device. Always bet to keep your PC's clock referenced to such a more
accurate source.

Internet updates are prone to latency errors , so do not expect better
than plus or minus about 1.5 seconds in that realm.

The phone or GPS device is the clear winner, and a good modern wrist
watch usually tracks those pretty well once set. Usually within mere
seconds per year. The phones are ALWAYS accurate as they are ALWAYS
constantly updated.

 

I've done it. The backup function of the battery means the circuitry
only draws battery power while power is OFF (and I do mean OFF,
'standby' of ATX power supplies is an ON state, even though
the computer seems powered down).

There's also a hold capacitor, usually a few seconds of power is assured while
swapping the coin cell.

 

Thanks. Now I've got to find that sort of utility, somewhere.

If I had a flash update utlity

So I assume even with a running PC one would still have to hook up a 3V
supply in order not to lose data?

No clue, I think it's a Foxconn G33M mobo in there.

Actually, without web updates the RTC in this PC was remarkably accurate
for all those years. Well, until yesterday. I rarely had to set it.

 

So maybe I should just hot-swap then.

That's odd. Because the PC here is always sent to hibernate and the
power is turned off. But it remains connected to 120VAC. Still, this
morning the RTC was off again by more than five minutes from yesterday.

And then the coin cell slips and our dog carries in to the kitchen,
"Look, ma, I found bling-bling!"

 

Done, new battery is in. Did a power-down into hibernate, came back up
like usual. The old battery still measures 3.272V but when loading it
with as light a load as 10k it collapses to 2.5V. With 1k it goes to
1.6V. So I guess the old battery was truly exhausted. It was made by
"Newsun" in Japan, never hear of that brand.

While I had the PC open I saw that I have quite a build-up of dog hair
in there, got to take it apart and clean it. Our big lab likes to curl
up down there when I am doing SPICE runs and warm air comes out. It's
amazing how tight of a space they can snuggle themselves into.

Supposedly there is a Dell tool but I haven't found it yet.

Thanks for the help, Jeff.

 

It ain't the same. In his opinion

Unfortunately on the Dells the intake is on the left side and that's
exactly where the Labrador snuggles up. Raising the PC would not help
but make it more prone to keeling over. For example when he hears the
Fedex truck and tries to travel from underneath the PC table to the
front door in milliseconds.

What makes it sweat is when you are almost done with a switcher and then
have to enter real xfmr coupling of 0.97 and such. Important to gauge
the dissipation in snubber parts. That really taxes a PC.

I guess then the digital camera is the only option. Or paper and pen

 

Joerg Inscribed thus:

Don't mess about ! Do it live. Use an anti static strap. Take care not
to damage the cell holder while removing the old battery and don't let
it flip out onto the circuit board. Make sure that you put the new
battery in the right way up, positive uppermost.

It should not take more than a few seconds to do the swap.

PS. A wood or plastic toothpic might help depending on the holder type.

HTH.

 

Joerg Inscribed thus:

A tip that might be usefull... A yellow led with the leads sprung across
the battery will give an instant indication of the battery state.

 

Well, it's already done. So not I am wondering about the laptops.
They've got to have such batteries as well. Maybe time to check those out.

 

yeah. but be careful if you drop it it could short something out,

 

The BIOS flash is not the config CMOS NVRAM

dead battery is about 50 ohms and 2.7 volts

NTP is much better than that.

 

That's $10. I use Time synchronizer from Softnik Technologies. Better yet,
it's free. http://time-synchronizer.software.informer.com/

 

Why does the change have to be quick? Isn't the circuit powered as long
as the laptop is? Because then one could solder in a new battery and
re-use the connector instead of shelling out lots of dough for a
specialty battery plus shipping charges.

Hey, it's nice, this morning the PC showed the correct time again

What I really don't understand why in this day and age they don't write
the settings into flash. I mean, we even successfully do that on totally
cheapo uC design.

 

That was not a very smart decision by the industry. Serviceablity has
suffered as a consequence.

And we know how that does. Battery is out ... cell phone rings ... oh,
got to take this one real quick ...

My iron can be operated sans ground. With a laptop it's not really that
tough anyhow because one can unplug the charger (many of those aren't
grounded anyhow). Just watch for ESD.

Whoops

Not really. Almost everything beyond 0Fh gets written once and then left
alone the next five years of so. Ok, maybe someone buys a new drive and
enters that. This would cause two write cycles to that location in five
years.

 

If you're using Windows (XP and up for sure, don't remember about 2000),
it has a built-in time sync functionality, *as long as the machine is
not part of a domain*. Just go to the time and date settings in Control
Panel and you should have an option for "Internet Time". It will
default to the server time.windows.com (which probably round-robins to
several machines at Microsoft) but you can add other servers if you
like.

If your Windows machine is part of a domain, its time is synchronized
from the domain controller as part of the networking protocol. If the
domain controller is listening to an Internet time server, then it will
propagate the correct time to its clients.

If you have old Windows or otherwise want some kind of independent
time-setting software, nistime-32bit.exe is free of charge from
http://www.nist.gov/pml/div688/grp40/its.cfm . It says: "The program
can be configured to query the server periodically and run in the
background." I have used it before on Windows 98 and it seems to work
OK; the minimum query interval is one hour. That NIST page also has a
link to a list of other time-setting software for various OSes.
(Trivia: it's called -32bit.exe, not to distinguish it from the 64-bit
version, but from the 16-bit version!)

If you have Linux, you can run ntpd. Most recent distributions do this
and provide some kind of happy clicky control panel. The real skinny is
in /etc/ntp.conf . ntpd can get its reference time over the Internet,
or from a local GPS receiver.

I don't know what OS X runs under the hood but I wouldn't be surprised
if it's some flavor of ntpd. The knobs are apparently at Applications >
System Preferences > Date & Time .

Matt Roberds

 

Same here, I think we somehow must have the same forefathers

Although my dad was a pro when it comes to programming, and so is my
sister, so maybe it's just me who didn't get the programmer's gene or
where it mutated into a circuit design gene.

Wouldn't it be a zero-cost piece of cake to at least write those to hard
disk and in case of finding a blank offer the user to restore from
there? Also, the BIOS is in flash so why not store there instead?

It would behove the industry to think about this because there is one
major reason why PC sales are slumping: The things became to darn
complicated for ol'Leroy. He does not want to face a pricey Geek Squad
call every time some obtuse "unrecoverable error" has occurred. So he
invests his money into a smart phone instead. Because that's not
complicated. A PC is complicated.

 

Internet updates are prone to latency errors , so do not expect better

Yep, though on windows you need Meinberg for NTP. Windows Time service
isn't as good. Linux real real NTP.

Tuning up NTP is a bit of work if you want to be optimal. Even though
people claim the accuracy is independent of the time reference, I make
it a point to find servers close to me (less hops) and that experience
low jitter, which can be determined via logging features of NTP.

I have found that running the antivirus check will effect the NTP
accuracy. It pays to plot the time error and then correlate it to known
time dependent programs.

You should be able to get the time error under 20ms.

 

Get it to synch to your phone and you'll get better accuracy than that.

Call NIST directly with a hard connected modem and you can get within
2ms. Regularly. Every time.. repeatably.

Your claim of 20ms is falsely based. Do it 25 times, and I'll bet you
get 25 different offsets from the real. So more likely plus or minus
about 80ms. You could probably get closer by hand synching to your phone
with the mouse click.

 

11000km in <2ms ! I don't think so.

25 times? ****! do it a million times the offset is still always under 5ms,
and that's using third tier timeservers.

These graphs are from someone else's server but are typical of a
carelessly installed NTP setup:

http://www.papy-team.org/munin/org/papy-team.org/ntp_offset.html