Sucking life out of cmos battery

[Paul]

Hi all,
I AM BAFFLED BY THIS ONE MY FOXCONN MOTHERBOARD CMOS BATTERY IS DISCHARGING EVERY COUPLE OF WEEKS HAVE CHANGED CMOS BATTERY TWICE WITH KNOWN GOOD ONES AND THIS IS THE THIRD ONE THAT HAS THE LIFE SUCKED OUT OF IT AGAIN. I HAVE CHANGED THE POWER SUPPLY THAUGHT THAT MIGHT BE THE PROBLEM. STILL THE SAME SANEREO.DON'T KNOW WHAT ELSE TO TRY?. YOUR INPUT TO THIS ONE WOULD REALLY HELP ANY IDEAS TO WHATS GOING ON. I KNOW IF I CHANGE THE CMOS BATTERY AGAIN AFTER A FIEW WEEKS I WILL HAVE A CMOS CHECKSUM ERROR AGAIN. I REALLY NEED TO KNOW WHATS CAUSING THIS PROBLEM SO I CALL ON ALL OF TECHNIBBLES TECHIES ON THIS ONE, THANKS GUYS AND GALS.

 

[NYJimbo]

Is this a new board?. If not how long into its life before it started doing this ?

First take out the suspect CMOS battery and check it with a voltmeter to be sure it really is the culprit. Checking isnt always valid as some bad batteries will show near 3.x volts because they are not under load. But at least you can get an idea. If you leave it wired to the meter for a little while it should not start draining quickly.

Second be sure your motherboard CMOS/BIOS jumpers are not set to "clear" or "reset". A machine can boot and run on many mobos even with this set wrong.

Often a short will cause this, buts its usually with a new board.

 

[Paul]

It's not a new motherboard i got this board- computer as a trade in about 5 months ago and have been changing cmos battery every fiew weeks.i will take out cmos battery and check voltage last two cmos batterys when checked with metre gave a reading of 0.73 volts even though when checked before inserted gave a reading of 2.98 volts.
Will check cmos jumpers and get back to ya nyjimbo. Will try all you said. Thanks

 

[NYJimbo]

It's not a new motherboard i got this board- computer as a trade in about 5 months ago and have been changing cmos battery every fiew weeks.

But that technically makes it a "new motherboard". I mean since you have owned it you have had to replace the battery, is that right ?.

 

[Paul]

YEP THATS RIGHT EVER SINCE I GOT IT HAVE TO CHANGE CMOS BATTERY.

HERES THE SPECS OF BOARD
Manufacturer Foxconn
Model 965X7AA
Version FAB1.2
Serial Number UYAF64101192

North Bridge Intel P965/G965 Revision C1
South Bridge Intel 82801HB/HR (ICH8/R) Revision C1

CPU Intel(R) Pentium(R) D CPU 2.80GHz
Cpu Socket Socket 775 LGA

System Slots 4 PCI

Memory Summary
Maximum Capacity 4096 MBytes
Maximum Memory Module Size 1024 MBytes
Memory Slots 4
Error Correction None

 

[Paul]

is this a new board?. If not how long into its life before it started doing this ?

First take out the suspect cmos battery and check it with a voltmeter to be sure it really is the culprit. Checking isnt always valid as some bad batteries will show near 3.x volts because they are not under load. But at least you can get an idea. If you leave it wired to the meter for a little while it should not start draining quickly.

Second be sure your motherboard cmos/bios jumpers are not set to "clear" or "reset". A machine can boot and run on many mobos even with this set wrong.

Often a short will cause this, buts its usually with a new board.

ok i have checked the cmos jumpers on motherboard and are on pins 2-3 which is in normal position, took out cmos battery and checked the voltage which gave a reading of 0.12v as i said when this and the other two i put in were all reading 3v to 2.89v and then got the life sucked out of them????????

 

[PcTek9]

Paul,
this is the capacitor at the end of the power supply. As it starts to short internally the resistance lowers, and it drains cmos batteries like mad. You can replace the power supply, or if you are a certified electronics technician, and / or have degrees in electronics. (LOL) you can obviously open the psu and replace the cap, of course making sure it's unplugged. These caps toward the end of the pc's power supply are called filter caps, they filter any remaining ripple out of the wave form to make a good solid dc signal with no ripple on the scope.

That's why there are several and why they go progressively downward in size all clumped up together. The smaller ones generally have lower MicroFarad storage ratings to clip the peaks of progressively smaller waves and remove any ac signal altogether to provide a solid stable straight line at whatever voltage is on the busbar at that point.

When you changed the psu did you use a known good one? Some of these coming from china and taiwan all have this issue. Did you use a 'different' brand of psu (good quality?)

If you really do have a good psu then it could be the cap right next to the cmos battery on the motherboard leaking internally, and not even showing any popped top or external leakage. Its possible the cap backing up cmos is ruptured or leaking internally. If you feel comfortable desolder it, and take a capacitance meter to it and see if it maintains its rated uF or if it's leaking. If it's leaking voltage internally, it will be like placing a small resistor directly across the battery terminals so that the battery slowly discharges, yet still much faster than anticipated. Instead of years it lasts a month.

But usually we always see this on the cheaper power supplies. * I dont know if you saw the article but there was a huge kadoo about a ton of bad caps being sent to the u.s. of a..... in power supplies. Goodluck.

 

[cecox]

Sucking life out of cmos bettery

I've seen that problem once before. In my case it turned out to be a shorted capacitor. There is a small electrolytic capacitor that is insereted in parallel to the CMOS battery. I believe its there to hold the charge long enough to let you replace the battery. It looks like a tiny beer can and is typically very close to the CMOS battery. IF you feel confident using a soldering iron and have a the equipment need to remove solder (solder sipper) the capacitor can be removed. Its not that difficult and it's better than replacing CMOS Batteries.

 

[Paul]

paul,
this is the capacitor at the end of the power supply. As it starts to short internally the resistance lowers, and it drains cmos batteries like mad. You can replace the power supply, or if you are a certified electronics technician, and / or have degrees in electronics. (lol) you can obviously open the psu and replace the cap, of course making sure it's unplugged. These caps toward the end of the pc's power supply are called filter caps, they filter any remaining ripple out of the wave form to make a good solid dc signal with no ripple on the scope.

That's why there are several and why they go progressively downward in size all clumped up together. The smaller ones generally have lower microfarad storage ratings to clip the peaks of progressively smaller waves and remove any ac signal altogether to provide a solid stable straight line at whatever voltage is on the busbar at that point.


When you changed the psu did you use a known good one? Some of these coming from china and taiwan all have this issue. Did you use a 'different' brand of psu (good quality?)

if you really do have a good psu then it could be the cap right next to the cmos battery on the motherboard leaking internally, and not even showing any popped top or external leakage. Its possible the cap backing up cmos is ruptured or leaking internally. If you feel comfortable desolder it, and take a capacitance meter to it and see if it maintains its rated uf or if it's leaking. If it's leaking voltage internally, it will be like placing a small resistor directly across the battery terminals so that the battery slowly discharges, yet still much faster than anticipated. Instead of years it lasts a month.

But usually we always see this on the cheaper power supplies. * i dont know if you saw the article but there was a huge kadoo about a ton of bad caps being sent to the u.s. Of a..... In power supplies. Goodluck.

I used a good known psu: Colorsit switching power supply: Model 400u. Intel 1.3 version p4 i have used another known good psu with same results to cmos battery, must be the cmos capicitor leaking internally no sign of external leakage. Thanks again for putting me out of my misery.well done to all for your help.