Hotwiring a computer isn't a particularly useful skill. But sometimes, it's nice to be able to start a computer that has a broken power switch. Especially if it's your only computer, and you've got to write some code for an impending launch.

I came to work on Monday morning, and turned on my computer1. The power LED and cooling fan came on for about three seconds before dying again. I tried pressing the power button to no avail; it was jammed.

Not only was the power button jammed, but I actually took the whole case apart trying to get at the back of the switch. No good; the back of the switch has the wires glued into it, and it's just a solid assembly. No user-serviceable parts here...

I was frustrated now. I'm a software engineer, so I don't usually crack open the cases of computers, and it's especially frustrating when it doesn't even fix the problem. I was talking my situation over with a coworker. He asked, "What's the switch connected to?" And then inspiration struck.

At this point, it's worth going into detail about how these switches work. In the old days, this might have been a dangerous operation: the switches are actually part of the power supply, and those things are plastered with warnings about electrocution risk. Then again, those switches tend to be of a sort that I wouldn't really expect to break.

These days, motherboards have advanced power management features. Among other things, this means that the motherboard somehow controls whether or not it gets turned on. This means that it can do interesting things like be connected to an Ethernet and wake up when another machine pings it on the network. It also means that modern power switches are allowed to be more complicated (and therefore exponentially more likely to break2). They're typically switches that just close the circuit momentarily.

It turns out to be pretty easy to turn the machine on. I already had the case off, so I could get at the motherboard. Then, disconnect the power switch from the motherboard (it's useless anyways, right?) Now, take a jumper off a hard drive or other device that isn't in the computer you're trying to turn on (I happen to have a clock made out of a hard drive sitting on my shelf at work...3)

Attach the jumper to the pins that the switch used to be connected to. Wait a few seconds. Take the jumper off.

Watch the computer whirr to life.

You could probably use most anything that conducts electricity for the magic step above, but using a jumper has the advantage that you won't accidentally connect two pins that aren't supposed to be connected as the computer starts powering up, which might cause something strange to happen.

And of course, the obvious solution (why do obvious solutions never occur to me?) is to wire up the reset switch to the power switch, since in an ATX machine (and most machines these days are) the power switch and the reset switch are wired the same. (Thanks, lj, for this suggestion.)

  1. I don't do this often. I usually keep myself logged in. But I was just moved into a new cube, and my machine was powered down to make things easier on the movers.
  2. KISS. I'm thinking here of the difference between power switches on the IBM XT, (which was this large sturdy red thing which I could never see breaking in any way) and the switches on all of my recent computers (which are these things that you push in, and are spring loaded to come back out, and only close the circuit when they're pushed all the way in.)
  3. It runs backward, too.

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