Dead Battery

[FORTRANS]

Hi,

   Anybody have some experience with a Dallas DS12887 Real
Time Clock?  The thing has the CMOS setup RAM and the battery
to preserve the RAM contents.  A computer has one with a failed
battery.  I assume that it will not recharge if the machine is left on.
How easy is it to replace or modify one of these?

   Or do I just pull the hard drives out to salvage my data?  The
larger drives are not seen, and the setup parameters cannot be
changed.

   Swapping the drives to the primary IDE controller may not be
easy if I want to boot it up.  I had a disaster with this one when
the drive configuration changed and something lunched the
partition tables on the old drive on the secondary controller.

Regards,

Steve N.

[dedndave]

the DS12887 seems to be a compatible replacement of the old MC146818
i am guessing a NiCad battery ???

the old NiCad circuits charged by using a diode (and usually a resistor) from the +5VDC source
they changed over to using lithium batteries, so many of the OEM's just left the charging parts out
lithium batteries don't like to be charged and may even explode   :P

my advice would be to remove the charging circuit and replace the battery with a 3V (# CR2032) lithium
you can get the CR2032 battery holders at radio shack, etc

[FORTRANS]

Hi Dave,

   No, it is a lithium battery.  With Google I found pictures where
they had removed it, broke into it, removed the battery, and
soldered wires to replace it with a 2032 button.  The pictures were
rotten.  I have no idea what they really did.  But that would also
require complete disassembly as I can hardly see it.  Much less
grab it and see if it is soldered to the board or socketed.  Getting
a soldering iron in there...  No way.

   If it is in a socket, and it is common enough to buy one, that
might be the way to go.  Anybody done that?  But I am thinking it
is time to free up some desk space.  It was used with a flat bed
scanner.  And that has died as well.

   So, getting the scanned pictures and image processing programs
is the main purpose of this exercise.  I was hoping to do it by
copying everything to an external hard drive.  Which would have
been relatively easy.  Too bad, yank the drives or replace the RTC
module.  Replacing the RTC might be easier if it can be yanked.

Regards,

Steve N.

[dedndave]

i don't think the programs will run - maybe - lol
if there are wires soldered in there - see if you can extend them and bring them out
if you can't solder - maybe some mini-alligator clips ?

i don't think replacing the chip gets you anything, unless the chip has failed

[FORTRANS]

Hi,

   The DS12887 is a module with a built in battery.  So replacing
it gets a new battery installed.  I will look again on google, but
the wires one mentioned were from desoldering the old battery.
Another was using a DS12887A, did in the old battery, and
soldered wires to the pins on the module before he put it back
into the socket.  But I was having problems getting tech sheets
to see if the pinouts were the same.  I was encountering bad
links, odd popups, and corrupt PDFs for whatever reasons.
Google seems to be wearing out, getting tired, or whatever.

   I guess I need to see if it's soldered to the motherboard before
I make further plans.  Is there a good way to solder leads to a
battery?  I have tried that before without much luck.  Makes a
nasty mess when done wrong.

Regards,

Steve N.

[dedndave]

close   :P

the dallas part may have all the oscillator parts internal
so - that would explain those N.C. pins
not sure about the others

[Mike Mayerhoffer]

Since I do not a clue to the age, some boards allow you to put a battery pack with a 2 pin connector or 4 pin by moving a jumper.

Any chance on what type of mother board it is. That might be easer to look up the layout for jumpers for an external batter pack plug using 2 or 3 AA battery pack made for this purpose  if it has jumpers or you can put the external battery pack with a plug, no soldering, no fuss, no mess. - just by moving a jumper - not to confuse it with the cmos clear jumper.

Just not sure -  MB number or pc model would be a good place to start looking for that info.

Don't heat or stress a lithium, they can start to burn fast and hot , no putting them out and water it will make matters worse.

Here is direct link to  the spec sheet from Maxim

http://pdfserv.maximintegrated.com/en/ds/DS12885-DS12C887A.pdf

Mike

[FORTRANS]

Hi,

   Thanks for the link to the PDF.  That got me a good copy,
unlike what I was seeing before.  If I read it correctly, then there
cannot be an external battery pack.  But that would have been
a nice idea.  Please correct me if I read that incorrectly.

   I do not see a brand name, only a serial number, probably a
part number, and made in Ireland.  I had thought it was an Intel
part using a Neptune chipset, but looking at some pictures it
might be based on the "Plato(?)" set.  Of course I can only see
part of one side of the motherboard without taking it out.

   Anyway, the RTC seems to be soldered to the motherboard.
So, that seems to answer the main question.  Oh well, too bad.
Planned obsolescence?  (Grumble.)

Regards,

Steve N.

[Mike Mayerhoffer]

Hi Fortran
you are correct - was a little tired when I posted.  FWIW Typically the internal batters on those RTC last minimum 10 years. It is just for retention or keeping the internal oscillator running and ram for the RTC time events and such it is not for running the RTC, just for sleep.

On your machine the RTC and CMOS/Bios is two different chips -the on board lithium battery actually ends up supplying the RTC VCC pin when board is powered up. If the on board lithium is dead the RTC does not work and power to the cmos is low and or missing. 

They are suppose to isolate the internal RTC battery and the on board lithium battery from an external power sources , putting power on non rechargeable lithium  is a fire hazard and  if I recall very toxic when lithium burns or the battery chemistry over all. You can not put them out it is a violent hot fire ball and very dangerous.

They get around this - buy having the onboard battery always supply the CMOS/BIOS   - when the power is on, they bias a transistor to connect a path from the on board battery to the RTC run VCC pin.
When this happens the RTC goes from sleep to full working mode supplying time to the Bios. They might have a little tickle to that on board battery, it is very  bad ideal imho.

Hope that helps.

Good Luck

Mike

[FORTRANS]

Hi Mike,

   Thanks for the response.  I was hoping someone had some
experience with one of these.  A trickle current (if it exists) might
have a recharge effect.  So leaving the computer on might help
one last time.  But that has not happened.  While the clock works,
the CMOS memory will not update.

   Ten year lifetime?  Well I guess I will just have to pretend that
I got my monies worth.  Some of the files indicate it came in
January 1995.

Regards,

Steve N.

[dedndave]

i guess i would try to disassemble it to the point where i could get at things
maybe that's easier said than done - lol

[FORTRANS]

Hi Dave,

i guess i would try to disassemble it to the point where i could get at things

   Well, next step is getting the two drives on the secondary controller
out and back them up.  Then see if getting the motherboard out
uses a finite amount of effort.

maybe that's easier said than done - lol

   Hardest part will be finding an open space to fill up with computer
parts.  Most good flat space has something on it already.  Time
to pick up a few boxes of books and DVD's and move them to
the back.

   Might be fun to try and cut the top of the RTC off and see what
that battery looks like.  Sounds like a plan of sorts.  Hope the
polarity is really obvious.

Cheers,

Steve N.

[dedndave]

you should be able to use the chip pinout to determine the polarity

as for the flat space - lol
use a piece of corrugated cardboard
you can punch the screws into it to form a "roadmap" of where they came from

[FORTRANS]

Hi,

   Well, yesterday I got the two unrecognized drives out and
revived another computer (replaced a dead battery).  Then got
one of them mounted in it.  And after the usual problems with
drive letters changed, verified the data is still there.  Only took
about ten to thirty times longer than it should have.  Getting too
slow and clumsy I guess.  Oh boy, old computers have a lot of
screws, that are not the same, but look almost the same.

   And I should have looked around a bit inside before closing it
up.  I have some network cards around, one of them should fit.
Any opinions on just putting the other drive on the cable without
any mounting?

Cheers,

Steve N.

[dedndave]

in win98 days, i had one machine with the cover off
the drives sat in there, unmounted, so i could swap fast
drives were in the 1 to 30 gb size range, at the time

i suppose some amount of "heat-sink" dissipation by mounting occurs, though