Question Cmos battery dying in few days Asus tuf b550m

[terminator1983]

I have Asus tuf b550m motherboard its cmos battery is dying in few days what is the problem is it because of motherboard or something else.

 

[jay32267]

If it is dying in a few days I would think it would have to be the motherboard and possibly some sort of current leak.

However I find it odd. It's not something I normally come across.

 

[TommyTwoTone66]

Sounds like a short on the motherboard.

 

[jay32267]

If it takes a few days...it is not a short.

If it was a short it would die instantly.

 

[TommyTwoTone66]

If it takes a few days...it is not a short.

If it was a short it would die instantly.

Depends what is shorted. If it’s an LED then it could work for weeks. If it’s a MOSFET or something then maybe a few minutes.

 

[terminator1983]

If it is dying in a few days I would think it would have to be the motherboard and possibly some sort of current leak.

However I find it odd. It's not something I normally come across.

Yes i have owned different computers but never encountered such problem. My last pc is working for more than 10 years and the cmos battery is still working fine.

 

[terminator1983]

Sounds like a short on the motherboard.

Any way to check that ? like with multimeter

 

[TommyTwoTone66]

Any way to check that ? like with multimeter

If you had about 50 hours to spare and the worlds steadiest hands, sure.

I would throw the board out and buy a replacement personally.

 

[jay32267]

Depends what is shorted. If it’s an LED then it could work for weeks. If it’s a MOSFET or something then maybe a few minutes.

No.
A short will drain the battery almost instantly.
If an LED is truly shorted it will also drain the battery almost instantly.

 

[TommyTwoTone66]

No.
A short will drain the battery almost instantly.
If an LED is truly shorted it will also drain the battery almost instantly.

can you describe what a “current leak” is without using the word “short”?

 

[jay32267]

Any way to check that ? like with multimeter

Maybe.

The capacity of a CR2032 is 235mAh.

For it to drain in a few days....it would have to drain at about 4mA.

The voltage is 3.

I would set the multimeter to resistance and take the battery out and measure across the battery terminals.

It's important to use the correct polarity on the meter.

When meters measure resistance....one probe is positive voltage...you need to know which....it isn't always the red one. This goes on the positive battery terminal.

If you see around 1000 ohms (which is near what you would expect for 4mA)....I think that would confirm motherboard problem.

 

[jay32267]

can you describe what a “current leak” is without using the word “short”?

The current involved in a "current leak" is usually orders or magnitude smaller than the current involved in a "short".

 

[TommyTwoTone66]

The current involved in a "current leak" is usually orders or magnitude smaller than the current involved in a "short".

What is a current leak though? How would one occur?
The only way for one to occur, to my (electronic engineering qualified) mind, is for there to be a short, somewhere in the curcuit.
If the short was directly on the battery, sure, it would drain it very quickly. But if it was on some lower powered component then likely not.

 

[jay32267]

What is a current leak though? How would one occur?
The only way for one to occur, to my (electronic engineering qualified) mind, is for there to be a short, somewhere in the curcuit.

Think of a current leak as "slow".
Current leaks are usually measured in millamps.
The resistance involved in current leaks are usually in teh order of kohms to Mohms.

Shorts are "fast".
Very high currents.
Very low resistances near zero.

A current leak can occur due to many things.
...breakdown of material is very common.

Think of a short as a really really bad current leak.

 

[drea.drechsler]

...
I would set the multimeter to resistance and take the battery out and measure across the battery terminals.

It's important to use the correct polarity on the meter.
...

And equally important to disconnect power and remove the PSU connections to the motherboard. Probably also remove USB devices.

This is mainly to be safe and avoid possibility of spurious readings.

 

[drea.drechsler]

...
Shorts are "fast".
...

Terminology is funny...a resistive short wouldn't be fast, but you call it a 'leak', which I never heard used in this context in any of my technical schooling. It was always called a resistive short.

 

[jay32267]

And equally important to disconnect power and remove the PSU connections to the motherboard. Probably also remove USB devices.

This is mainly to be safe and avoid possibility of spurious readings.

^^^^Agree.

But also....the whole idea may not work regardless because we really don't know what's between B+ and ground. It was just something to try.

 

[jay32267]

Terminology is funny...a resistive short wouldn't be fast, but you call it a 'leak', which I never heard used in this context any of my tech schooling. It was always called a resistive short.

"resistive short" isn't a term I come across and I've been an EE for 40 years.
I also did not come across the term "resistive short" while obtaining my BSEE or BSPhysics.

I think it is a confusing term.

It uses two words that basically mean the opposite of each other.

 

[drea.drechsler]

"resistive short" isn't a term I come across and I've been an EE for 40 years.
I also did not come across the term "resistive short" while obtaining my BSEE or BSPhysics.

I think it is a confusing term.

It uses two words that basically mean the opposite of each other.

LOL...and we used it extensively in my EE schooling as well as tech school training and my job...funny.

Well, have a good one. Maybe you should write a book to standardize it to your liking.

 

[jay32267]

LOL...and we used it extensively in my EE schooling as well as tech school training and my job...funny.

Well, have a good one. Maybe you should write a book to standardize it to your liking.

Maybe you had an instructor that like that term.

In the real world automotive industry, on schematics and prints that specification is almost always referred to as the "leakage current specification".
The terms leakage and leakage current are used extensively in many technical documents throughout the industry.
The hipot industry.....which specializes in this...also refers to it as leakage and leakage current.
The term "resistive short" is extremely rare.
.

 

[drea.drechsler]

Maybe you had an instructor that like that term.

In the real world automotive industry, on schematics and prints that specification is almost always referred to as the "leakage current specification".
The terms leakage and leakage current are used extensively in many technical documents throughout the industry.
The hipot industry.....which specializes in this...also refers to it as leakage and leakage current.
The term "resistive short" is extremely rare.
.

I think the difference is in the context of reference...

In my experience, we refer to it as a resistive short when it's undesireable in the circuit, as would be the case with OP's problem. Leakage currents may flow, or indicate on an ohm meter as high resistance, as a function of circuit design...or possibly a defect until diagnosed. This was in aerospace, mainly bed-of-nails in-circuit testing where distinguishing the two conditions is desireable. Actually, three if mixing 'dead short' in with it.

 

[jay32267]

It's just preference.
I don't care for the term because I think it conflicts with itself.
I spoke with a bunch of the other EEs here where I work and they don't care for the term either.
...but I don't think in a practical sense it much matters. I understand what is meant by it.

 

[egda23]

Could it be a matter of 'american english' versus 'english english' versus 'australian english' versus 'rest of the world english' ?? 😳

 

[drea.drechsler]

Could it be a matter of 'american english' versus 'english english' versus 'australian english' versus 'rest of the world english' ?? 😳

Very possible..I've never 'earthed' a darn thing in my life for instance (except maybe my face sliding into home plate in 6th grade). But they do that all the time in england. I ground myself before picking up a microprocessor, though, and would check facility grounds on a daily basis in the test labs.

But funny, to me calling it 'leakage' is very confusing as leakage is a normal element of circuit design and inherent in all semi-conductors even if undesireable. It's something the TE has to characterize at each node for in- circuit testing. So to say 'there's leakage at that node' means nothing beyond a simple statement of fact. But to say there's a short...a resistive short if not a dead short...is descriptive of it's defective state and can serve to avoid confusion in conversation between the TE and the tech who'll effect rapair.

 

[InvalidError]

Coin cell batteries have a short-circuit current of 10-50mA and will take a few hours to fully discharge even when shorted out, that is how key-ring LED lamps can work without bothering with current-limiting resistors, so you can add an intermittent short to the laundry list of potential causes.

Under normal circumstances, the clock/CMOS circuitry would run from 5VSB. For the battery to die, something must have gone wrong there unless you are hard-switching the PSU off between uses. If you leave the PSU connected with 5VSB available, the clock/CMOS battery should last 10+ years - I have yet to change the battery in my 17 years old P4 which I last turned on a couple of months ago to use my scanner.