Capasitors 2

[living4jesus]

We have an HP Pavillion xt963. Last night it was working fine and then we shut down and went to bed. This morning it wouldn't come on when we pressed the power switch. After checking the power cords and power strip it was plugged into, I did a search online and came across a thread from this group. The Thread # is 602-1224302. A man was having the same problem that I am having. He stated that he could hold the power switch down for 2 - 3 minutes and it would come on, so I tried it and it did come on. However, I would like to fix the problem. The man tried a suggestion from another user and said it fixed his problem. These are quotes from the thread:

"Last night/this morning I was up until 2 A.M. playing some online games. I shut down my computer a little while later. It wasn’t showing any problems. I woke up around 9 hours later and the computer wouldn’t start when I pressed the power button. Nobody had touched it while I slept. Whereas it won’t start up if you press the power button and let go immediately, I’ve found that if I hold the power button down for a while (2-3 minutes) the CPU fan starts and the rest of the computer starts within a couple more minutes. "

And later: "Hmmm. I drained the capasitors and it starts up now, which is great news."

My question is how to drain the capasitors. Any help would be greatly appreciated.

 

[SaishuHeiki]

Capacitors in computers are generally very small (in the range of nanofarads), and need recharged every ~50 ms (IIRC from my digital circuits classes).

Any larger capicitor will need less frequent recharging.

Therefore, just turning off the power and waiting a few seconds will be sufficient to let the charge drain from the caps.

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It is easier for an intellegent person to "play dumb" than for an unintellegent person to "play smart". - gbaughma

 

[edfair]

Power on requires the start key depression to activate the power up circuit on the board.
So far as I can recall there are no capacitors in the power up circuit that would fail in the way described.
I would consider the power supply the more likely culprit. That soemhow it is losing standby power.
You may have a board that indicats standby power with a LED. If so, you could know whether it is losing that supply.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[living4jesus]

Thanks SaishuHeiki. I did turn off my power stip overnight and the next morning the computer started right up at the first touch of the power switch. That was sure a relief!

Also thank you Edfair for your post. I have a follow up question. My pc's clock is not keeping the correct time and I need to change the battery for that. Could that be the problem with losing standby power? Also, is there a way to know what battery I need without taking it apart first?

Thanks again to both of you. This group is awesome!

 

[edfair]

The clock and the power up problem are not related.

Most modern M/Bs use a CR2032 coin type lithium battery. Most are mounted in a holder flat to the board and look like a nickel being held down by a strap.

Changing the battery may, or may not, fix the time problem. The clock chip uses a crystal for timing. I've had several problems over the years where the crystal was the problem. Not often, and fortunately several years ago, before the multi-layer boards.

Ed Fair
Give the wrong symptoms, get the wrong solutions.