discharging capacitors

[teddythemonster]

I've been told holding the power button in on my pc after it is turned off will discharge the capacitors on the motherboard.
Can any one verify this?

 

[Demon82]

More than when turned off, when disconected from AC power (through cable pull off of PSU switch), but yes, that's the concept.

 

[SerpentRoyal]

Disconnect power from PSU and hit the power switch. This should instantly discharge any power stored in PSU. Note that you're not discharging the caps on MB. To completely clear CMOS, you'll need to remove the battery and put the CMOS jumper in clear position. Wait 1/2 hour before re-assembly.

 

[Crusty]

Originally posted by: SerpentRoyal
Disconnect power from PSU and hit the power switch. This should instantly discharge any power stored in PSU. Note that you're not discharging the caps on MB. To completely clear CMOS, you'll need to remove the battery and put the CMOS jumper in clear position. Wait 1/2 hour before re-assembly.

If all you want to do is clear the CMOS then there should be no need to wait 30 minutes.....

 

[SerpentRoyal]

Some boards may need up to several hours to clear CMOS, especially if there is BIOS corruption. 1/2 hour should be a good for most. If there is no issue with BIOS, then the jumper method should do the job without the need to discharge the PSU.

 

[Crusty]

Any links to back that up? I've never had to leave the jumper set more then a few seconds. Long enough to put it on, take my fingers off, and then move it back...

If for some reason you really need all the caps on the board to be drained then yes you would have to wait... but not to clear the CMOS.

 

[SerpentRoyal]

No link...just personal experience. I'm sure other experienced overclokers will support my claims. There's quick CMOS clear, and deep CMOS clear.

 

[Crusty]

All the jumper is doing is breaking the circuit that provides power to the CMOS chip, once the power is cut the CMOS is cleared. It might take second or two to fully clear, but 30 minutes is a waste of time.

For instance, look at all of the articles on the Main page about over clocking all the latest mobo/chipsets, do you honestly think that they sit there for 30 minutes between every OC attempt? By the time they got all the tests done the technology would be outdated.

If you really screwed up your BIOS so much that you need a "deep CMOS clear" then chances are you are going to need a new BIOS altogether.

 

[SerpentRoyal]

You have your scientific explanation. Can you guarantee that there are no other caps on the MB that could be connected to the CMOS IC?

Why don't you start a poll to see if clearing CMOS for about 10 seconds is 100% effective? No need to go into a pissing contest.

 

[Crusty]

There shouldn't be any caps between the jumper and the CMOS, if there are any needed for the circuit it would be before the jumper. The jumper is just a manual switch, the only thing that needs to discharge once the switch is flipped off is the CMOS itself.

 

[SerpentRoyal]

So why not start a poll to prove your theory?

 

[MetaDFF]

Some ASUS motherboards have an LED to indicate that power is connected to the motherboard.

I wonder if that LED is sufficient to discharge the PSU and motherboard capacitors. I notice that when I unplug and turn off the PSU (via switch on the back of the PSU) that it takes a few seconds before the LED turns off, which to me seems to indicate it must be discharging the built up charge on the caps.

 

[Crusty]

Originally posted by: SerpentRoyal
So why not start a poll to prove your theory?

There is no need to "prove" myself, but there IS a need to stop the spreading of misinformation.

After some more research, from what I can tell there are two ways to clear a CMOS. First way is by using a control signal to force the erase, the other way is by basically connecting the CMOS to a Ground and letting the charge leave it thus erasing it.

The latter method could potentially take a few seconds to happen, whereas the signaling method would perform the reset on the next power on cycle.

There is no need to wait 30+ minutes.