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BlackRabbit 1st February 2009 10:41

CMOS battery keeps draining
I have had this problem for a while now, and it just keeps me annoying more each and every day.

One of my shuttles (SN G45 2) keeps forgetting CMOS data. After checking the first CMOS battery, it appeared to be empty. I replaced it but again - just a bit later - this new battery seems to be empty. This clearly isn't normal, but I can't figure out what the problem might be.. (note that no problems arise as long as the power cable is plugged in).

The CMOS-reset jumper appears to be put on the correct pins. However, I was wondering what would happen if I just left it out.. Can this cause harm to the system? What happens if you boot the system with the jumper in 'clear CMOS' mode?

Any other ideas as of what might cause this issue?


jmke 1st February 2009 10:44

did you email Shuttle support yet?
regarding clear CMOS jumper, some systems don't boot up if you have it on "reset"....

BlackRabbit 1st February 2009 18:59

I haven't emailed Shuttle Support (yet).
I was hoping to get some ideas here before doing that ;-)

Allow me to complete my story: problems began one day after the system had been running too hot for too long. Inside the case was a Ti4600 that got overheated as well (showed artefacts afterwards). My first guess was that the high temps in the case caused the battery to 'break'.

Now I'm guessing something - somewhere - did indeed break down, causing a minor short circuit (or something like it).

wutske 1st February 2009 22:34

There are a lot of components that don't like heat, so it won't be easy to find out which might have suffered from the heat.

The first thing I'd say is a damaged capacitor, they can get damaged by high temperatures which causes greater leak currents than normal. However, it's not easy to find a broken cap (except if it's realy broken and is about to burst :) ).

That's the only component I could suspect. A CMOS battery does nothing else but powering the CMOS and a crystal oscilator.

Kougar 2nd February 2009 04:31

If you have a multimeter or voltmeter, test out those batteries just to be sure they are actually drained.


regarding clear CMOS jumper, some systems don't boot up if you have it on "reset"....
There was one time I suspected a battery issue, but after testing the batteries were okay I realized I had the CMOS jumper set to clear CMOS by mistake and had gotten the position reversed.

I didn't realize it was in the wrong position because (as JMke said) in almost all cases motherboards I have used refuse to boot with the clear CMOS jumper set.

BlackRabbit 2nd February 2009 11:09

Yes, both batteries (the old one and the new one) are really drained (checked with voltmeter).

I was thinking that keeping the CMOS-jumper on 'reset' could drain the battery as well. The markings on the motherboard aren't very clear, so I figured I might have messed up this way. However, according to the manual, the jumper was installed ok (in default position).

Btw: already checked the motherboard for (visibly) broken capacitors, but found none.
Is there another way to check them? Measure resistance between pins?

Kougar 2nd February 2009 15:30

Plug in a new cell and start poking/measuring everything until something reads the same voltage as the cell?

Would guess it was shorting to ground, tried removing the motherboard completely from the case, too? Is just a guess. :)

BlackRabbit 19th February 2009 20:58

Is it normal that the BIOS mentions 3.05V for the VBat, even when there is no battery installed??

wutske 20th February 2009 09:33

Never tested before, but I guess VBatt refers to the 3.3v line running to the CMOS battery ?

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