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I'd like a technical explanation of a fix I've seen for some HP laptops.

The user turns on their machine only to find a blank screen; the screen doesn't even turn on, but all of the keyboard LEDs and the fan are running. The computer becomes very hot. I fixed this on my laptop after finding an answer here: unplug the laptop, take out the battery, hold down the power button for about 30 seconds, plug the laptop in (but not the battery), and turn it on. Another friend of mine always has to leave the battery out for the laptop to start.

I'd like to know how this sort of thing is possible. Did something in the circuitry break or melt? Is there a logic error in the design?

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It's possible that's a forced method to reset the BIOS if anything has gone wrong with it. –  Rob Nov 30 '11 at 20:09

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This happens if the capacitors on the board are overcharged; it's either a safety mechanism (to prevent overvolting, some motherboards do this) or simply a malfunction from the extra electricity. The act of attemping to power on the machine without a power source drains the capacitors, and voila - functioning laptop. There can be a lot of causes for this - static electricity, ambient humidity, unstable/dirty power source, problems with the battery, or even a problem with the motherboard itself. It shouldn't happen with any regularity unless there's a component problem, or alternatively you make your living doing belly slides on shag carpeting.

Note that this can happen, not just on laptops, but on desktop PCs as well. Beyond that, it can happen to pretty much any sufficiently sophisticated modern electronic device, in theory. Laptops are just especially susceptible due to their design, so it's generally the only place you see this behavior.

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It has nothing to do with capacitors. –  David Schwartz Nov 30 '11 at 21:47
    
@DavidSchwartz - I'll admit I'm no electrician, but this is the explanation I've always heard from people who are and the fix most certainly does work as laid out. I'll look forward to seeing your explanation. –  Shinrai Nov 30 '11 at 21:51
    
It just doesn't make any sense. How can a capacitor get "overcharged"? Where would the "extra electricity" come from? The computer is simply locked up, hard crashed. Removing the power source drops the supply voltage to all components to zero. It can't remain in a locked state with no power at all. The capacitors have nothing to do with anything nor is there any "extra electricity". –  David Schwartz Nov 30 '11 at 21:55
    
@DavidSchwartz - You're reading me wrong (and I think you're reading the OP wrong as well, it's not "crashed" because it never took off in the first place). It's not overcharged in the sense that it's got more than the capacitor(s) or even the system is designed for, it's overcharged in the sense that there is more charge in the capacitor(s) than there should be in a powered off state, which can cause some things to act weird when you go to turn it on, like say the motherboard not POSTing. As I said, how it got there is open to debate. I am not implying some magical electricity genie. –  Shinrai Nov 30 '11 at 22:20
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@David: Do you actually read what Shinrai said? There is more charge in the capacitor(s) than there should be in a powered off state. You are also contradicting yourself. First you say that you remove all power from the laptop and then you say that power is supposed to be in the capacitors, I don't see how listing both these after each other is constructive. Please also note that comments are meant to comment on the post and are not meant for discussion or debate... –  Tom Wijsman Nov 30 '11 at 23:43

The problem is that the laptop has crashed. Typically, some piece of hardware gets into an inconsistent or locked-up state, usually the part of the motherboard chipset that controls power sequencing itself. Because the power sequencer runs off standby power (otherwise, you couldn't turn the computer on unless it was already on), simply turning the power off isn't enough.

Removing the battery would eventually solve the problem, as all power would eventually deplete. But the laptop was never designed to drop its standby power all the way to zero as that's not supposed to happen under any normal operating conditions. To force it, you have to try to power the laptop on. That will drain all residual power from everything but the circuity that sustains the CMOS clock and BIOS setup information, which will unfreeze the laptop.

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