Did you check the clear cmos jumper?

A bit of a wild guess. I don't know if it is possible that a misplaced clear cmos jumper can be guilty of this.

Hi. Unfourtanely that 's not it. This board only has two pins near the battery instead of the usual three with a jumper plugged in two of them. If you want to clear the cmos you shorth them with either a screwdriver or a spare jumper.
Apart from the board having some faulty component, i can't figure anything else that i could do to easly fix it 🙁

Used to have a Pentium II that did this and never have fixed it... Yeah, I still have it but had to retire it because I got landed with a better board and the bug annoyed the hell out of me.

As I've just discovered that a connection to ground seems to trigger the reset, maybe it's a faulty capacitor that's gone short? Otherwise it could just be faulty CMOS RAM and I dread to think of replacing it on a board like that.

I don't care that much about my P2 as I just use that board as a testbed now, but I'll be watching in case you fix it.

You mean the bios chip? This one is socketed and the replacement would be easy but i don't have a equal spare board to try it out. As for shorts, i'll test with a multimeter later at night and feed you guys back if anything new happens.
This board was actually recapped around the cpu area, maybe a capacitor with the same brand near the cmos battery is dead shorted as well.

No not the BIOS chip - it is flash memory that only stores the executable firmware, not settings. Reseating it won't do anything except loosen the socket a bit every time you do it, so don't do it unless the motherboard does not boot because of loose or oxidized connection with BIOS chip.

The RTC the accompanying CMOS RAM that is used to store the settings are integrated into the chipset. Taking a look at the picture here http://static.kupindoslike.com/Asrock-775V88- … a_O_3344441.jpg, the battery is most likely connected to the big chip with VIA logo (and the cylindrical crystal just near SATA1 connector is most likely the 32768 Hz crystal for real-time clock so it also hints the CMOS RAM is there).

It could be that the battery or socket is dirty and cleaning both with a cotton swab dipped in some solvent like isopropanol could solve it.

It could also be a component failure, but the battery backup circuit rarely has big electrolytic caps involved so it must be something else.
So check the copper trace from battery to VIA chipset if there is anything out of the ordinary involved. Sometimes the battery power might go through some components (diodes and/or resistors for UL approval) and might also have some kind of capacitor to ground. If you have a multimeter you could measure the connectivity or if the battery voltage can reach its destination.

Now, a stupid question, but when you enter the BIOS settings screen to set time etc, does the time actually advance or is the clock halted?

Jepael wrote:

So check the copper trace from battery to VIA chipset if there is anything out of the ordinary involved.

I did it and there was!
The small resistor shown in the picture bellow connects directly to the positive of the battery and measured on circuit 999 ohms instead of 100\102 ohms, which is a dead give way of a resistor failure. Most likely it's completely open.

I've added axial 100ohms resistor just to check how it did and it worked! The bios now stays with it's settings even when unplugged from the wall like it should.

I would assume two options to justify this resistor failure:

1-Someone placed the wrong battery in the motherboard;
2-Most likely someone placed the battery backwards and turned the computer on, shorting this little resistor do ground.

Now i guess i just need to find a 100\102 ohm smd resistor in my motherboard graveyard..

Jepael wrote:

Now, a stupid question, but when you enter the BIOS settings screen to set time etc, does the time actually advance or is the clock halted?

The clock was working fine anyway 😀

Er. SMD resistor codes. 2 first digits * 10^(3rd digit). 102 = 10*(10^2) = 1kOhm.
That resistor has the correct value at 999Ohms. Best guess is that it's there to prevent the battery from draining too fast when clearing CMOS settings. (goes battery --> resistor --> right anode of that SOT-23 diode --> one pin of the jumper)

K45 is a standard SMD ID code for BAS40W-5 diodes.

The jumper shorts to ground. The diode likely works as a simplistic switch between 'system power' and 'battery power' when the system is on/off, preventing the battery from backfeeding into the rest of the system and prevents system power from backfeeding into the battery (which would be 'spontaneous combustion' kind of bad).

Have you checked the replacement battery itself when under load? It's possible its voltage was low to start with.

Ah, good, you got it working.

Guess what;

Seems to be the diode on mine actually, as putting the probes directly onto it yields the same thing in both directions; no continuity. The resistor also comes back as being dead though, so I'll replace both... Kinda wondering if I have a spare ATX case to hand now.

Edit: Diode in question is hidden behind the red probe in that image. It's not surface mount, which makes things easier.

Maeslin wrote:

Er. SMD resistor codes. 2 first digits * 10^(3rd digit). 102 = 10*(10^2) = 1kOhm. That resistor has the correct value at 999Ohms […]
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Er. SMD resistor codes. 2 first digits * 10^(3rd digit). 102 = 10*(10^2) = 1kOhm.
That resistor has the correct value at 999Ohms. Best guess is that it's there to prevent the battery from draining too fast when clearing CMOS settings. (goes battery --> resistor --> right anode of that SOT-23 diode --> one pin of the jumper)

K45 is a standard SMD ID code for BAS40W-5 diodes.

The jumper shorts to ground. The diode likely works as a simplistic switch between 'system power' and 'battery power' when the system is on/off, preventing the battery from backfeeding into the rest of the system and prevents system power from backfeeding into the battery (which would be 'spontaneous combustion' kind of bad).

Have you checked the replacement battery itself when under load? It's possible its voltage was low to start with.

Oh that's my bad, i really thought those were the actual values, to make things worse that 221 smd resistor also near to the battery socket actually reads 220 ohms on my multimeter so it made sense for the 102 to be the actual resistor value. But in your link 221 really means 220ohms.

I'm confused now if that takes me to square one or not because of i remove my axial resistor my bios settings are lost when i unplug the computer from the wall...

The battery reading while under load or not, with either the axial resistor i added or not measures always 3,02V so it should be ok. It's a brand new battery 😁

Yup, 221 does mean 22*10=220 and 102 does mean 10*100=1k, otherwise you could only have pretty unusable range of resistances between 000-999 ohms with three numbers.

The resistor is necessary to limit charging current towards battery in case of diode failure. Or in fact, since it is a schottky diode, it could leak some smallish amount of current towards battery from 5V supply if there were no resistor, so it is a standard safety requirement for lithium batteries (unless such a mechanism is built into the chips they are connected to).

Anyway, you measured the voltage at the battery, but you did not measure the voltage before the diode or after it. So you don't know if there is a short circuit which the resistor limits to max 3mA. However, when pulling 3mA of current from such wimpy battery, its voltage should be much less than 3.02V, so I think you don't have a short circuit. Maybe the battery voltage never passes to chipset (blown diode? battery socket has bad soldering?).

Measure the voltage from the diode pins with mains plugged in so you have standby supply, measure with mains unplugged so you know there is no other power source, and you could even measure it when you have the PC turned on. This way you know if the diode is blown. The diode is simple, battery voltage comes in, some 5V voltage comes in, and higher of those two input voltages comes out (minus voltage drop caused inside the diode which should be less than 0.3V).

Well i want to thank you both for your knowledge and explanations because it made me understand much better the "workings" of the cmos battery and cmos clear circuitry.

I've made this small schematic according to what i was able to pinpoint with my multimeter.

I measured 3,02v right before the "102" resistor and about 2,98v after it (give or take a few mV on these voltages). Then after that unmarked resistor that feeds the VIA chip i got about 2,66v. One thing that i would notice was that when the board was turned off and unplugged from the mains, if i shaked it even if a tiny bit, the voltage getting to the VIA chip after that unkarmed resistor dropped considerably to 1,5v or even less, and then back to 2,66 (it was all over the place sometimes). If i did the same thing but measured the voltage before that "102" resistor it was always above 2,5\2,7v, but in extreme cases it would get even lower than 2,5v, meaning that nearly no voltage was getting to the chipset.

Well, the only thing before that "102" resistor was the battery socket but i already had it cleaned with alchool a few times. Then i pressed the positive of the battery socket really hard with a screwdriver and the voltage wouldn't drop anymore with minor shakes of the board.
I couldn't believe, it was the battery socket all along?...I cleaned it again with KONTACT spray and bended the contacts really hard, tested it and the bios settings weren't being lost anymore!... I felt a bit bad for so much work and in the end it was a oxidized battery socket. D0H

But it doesn't end here...after i assembled the board in the computer case and turned it on the bios settings were LOST again -_-
I decided to replace that socket with one from a dead motherboard and now everything working has it should.

Incredible, so much work and it was so simple in the end 🙁
I know that you suggested dirty battery contacts but man...i had them cleaned with achool 97%...i could swear that the problem wasn't there.

I think that by adding that 100 ohm resistor in parallel with the "102" smd resistor i was involuntary able to "alleviate" the voltage drop caused by the oxidized(?) battery socket.

Btw pardon my ugly hand writing and have a laught about how my schematic looks like some weird robot from the 80's.

That's actually a pretty damn good schematic.

As you've learned, alcohol is unfortunately not all that great a contact cleaner. Won't help at all for corrosion, only for some forms of gunk (on other types of gunk, I've had to use brake cleaner before it had any effect!).

Something that may be useful for such situations is a combination of emery board (small nail file) and nail polish remover/acetone but you have to be careful with the latter because it will also do a mess of most plastics. The emery board is perfect for scarping corrosion off contacts.

Another alternative is a simple popsicle stick with a piece of super-fine sandpaper glued to it.

From the tests you've done, resoldering that unmarked resistor might also help. Dry or cracked solder joints on SMD components can be a pain to find and it can't hurt to touch things up a bit.

Maeslin wrote:

From the tests you've done, resoldering that unmarked resistor might also help. Dry or cracked solder joints on SMD components can be a pain to find and it can't hurt to touch things up a bit.

Will do, i just need to google a bit about ideal temperatures for the soldering iron when resoldering these small smds.