Pulling the plug out for 10 seconds

When calling support the other day he told me to reset my DSL modem by pulling out the power, leave it out for 10 seconds, and then plug it back in. This is something I have heard many times with different kinds of equipment. I have also heard it in relation to computers. That when you turn it off, you should wait at least 10 seconds before you turn it on again.

Why not just plug it in again right away?
Why 10 seconds, instead of, say... 3 or 30?
Should you really, always do this; just with certain types of equipment; just in certain circumstances; or is it just a "myth" thing that people have said so often that they believe it to be fact?

power-supply

Svish

Posted 2009-12-19T11:27:39.393

Reputation: 27 731

Answers

A lot of modern technology contains capacitors! These are like energy buckets, little batteries that fill up when you put a current through them, and discharge otherwise. 10 seconds is the time it takes most capacitors to discharge enough for the electronics they're powering to stop working. That's why when you turn your PC off at the wall, things like an LED on your motherboard take a few seconds to disappear. You probably could wait a different time, but 10 seconds is the shortest time you can be sure everything's discharged.

Phoshi

Posted 2009-12-19T11:27:39.393

Reputation: 22 001

1<3 It's important to know capacitors are in there - there's a lot of poor ones out there. If a capacitor breaks... bad things can happen, and some capacitors do just break, sometimes very quickly. It's a serious issue, but also an incredibly fixable one. Capacitors, unlike most modern technology, are pretty big, and easily replacable with a soldering iron and some wire cutters. – Phoshi – 2009-12-19T11:49:25.307

@quack; Well, unless you plan to pull the capacitors out with your bare hands... :P @Idigas; Yeah, but icky stuff happens :( My mum had a laptop with a load of popped Cs, nothing was wrong, except she couldn't write to the boot sector of her HDD (Which meant no reformatting), it puzzled us for quite a while until I looked inside and saw... goo, basically. – Phoshi – 2009-12-19T15:35:29.563

1@phoshi: i'll admit i haven't done it, but my first assumption is you'd remove the caps by desoldering them ... though wire cutters may be preferred to avoid damaging other nearby components. – quack quixote – 2009-12-20T15:22:46.907

I guess you could do that, actually. I've always wirecutted, THEN desoldered, because that's how I was taught it back in systems and control, in school, but just desoldering would probably work yeah :) – Phoshi – 2009-12-20T15:47:25.300

On modern boards, everything is mounted so tight that you're not going to be able to cut before desoldering. There's nothing to cut! The caps get soldered into a position tight against the board and then the legs are cut off from the other side. – Brian Knoblauch – 2009-12-21T13:23:45.373

2As far as the 10 seconds, I'm not sure that it's anymore than a "voodoo helpdesk" ritual. Most small electronics caps loose charge withing a second of power loss. Some systems may have caps that take days or even weeks to fully discharge too. – Brian Knoblauch – 2009-12-21T13:27:15.827

Well, the nature of the problem means I'm a bit behind the times. I haven't done it much, and then only on old stuff :P

I can assure you from personal experience, however, that it's not entirely voodoo. Partially, yes, but not entirely. Go on, do it now - flick your PC off at the wall, and look inside the case. If your mobo is anything like mine, there'll be a little light on it, that will stay lit for about 7 seconds - there IS some residual charge left in the system. – Phoshi – 2009-12-21T13:38:03.297

How about the practice of unplugging the device and then hitting/holding down the power button to discharge the caps? I've seen HP recommend this on their desktops... – atom255 – 2009-12-23T15:38:23.643

2I'd guess this does much the same thing - plus holding down the button makes sure you spend a bit of time waiting! – Phoshi – 2009-12-23T16:05:53.753

http://superuser.com/questions/27229/ethernet-port-troubles/27266#27266

It is by far just a myth!

– DHayes – 2009-12-29T20:24:05.880

I'd say more of a legend. It has elements of truth in it. – Phoshi – 2009-12-29T21:20:23.287

In my experience 0 seconds work just as well as 10 for restarting the equipment.

The reason in my opinion for the 10 seconds is only to ensure that the client has totally pulled the plug out of the socket. Some people just don't pull it out all the way unless they have to wait for X seconds with it in their hands.

harrymc

Posted 2009-12-19T11:27:39.393

Reputation: 306 093

1Reversing the ethernet cable also ensures that you actually have properly traced the cable. (Obviously only an issue if you have other ethernet cables--but this is quite possible even in a home environment. I have an ethernet-connected printer so it's available to machines on the Wi-Fi.) – Loren Pechtel – 2015-01-19T19:26:25.070

24More social engineering: A help desk Bob will tell you to reverse your ethernet cable. It's much more reliable than taking the user's word that it is, in fact, plugged in. :) – Richard Hoskins – 2009-12-19T17:49:20.697

Reverse your ethernet cable... hehe, that's brilliant :p – Svish – 2009-12-19T21:01:51.447

I think there are 2 topics going on here within this question:

The value of waiting a period of time after removing the power from an electronic device. YES, 30+ seconds is a good "average" time to allow Capacitors, hard drives, RAM memory, etc have the time to power down and be ready for the 'power on' reboot sequence.
The proper way to 'power down' an electronic device. Best 'rule of thumb' is if the equipment has an 'on and off' button or switch USE IT. It's there for a reason. As anyone with the knowledge of how a PC operates knows there are important 'startup' and 'shutdown' sequences the equipment goes thru. Allow the equipment time to power down and power up properly. These sequences are necessary for successful operation. Otherwise stress to hardware, stranded files, bloated 'page files', voltage surges, etc... can cause more problems, on top of the one you are trying to fix.

MyDWing

Posted 2009-12-19T11:27:39.393

Reputation: 41

+1 I have seen a power supply burned out by turning power off then right back on, without a pause. – Daniel R Hicks – 2015-01-17T13:33:22.327

Phoshi said well, but there could be another reason for that, a very less technical one: it is kind of related to social engineering.

The majority of customer care call center hires just...everyone! And there you could find someone that understand what you're asking, as well as someone who don't understand/don't care about, and the usual solution for every problem is (in the latter case) something like "Reboot" or "unplug and replug"! :D

Sadly, I saw that with my own eyes...

dag729

Posted 2009-12-19T11:27:39.393

Reputation: 1 894

Sometimes a reboot/unplug is used to get the customer off the phone if you contacted a call center. Call/chat center workers are graded on the time they are on calls, so for tough calls, they'll "dump" to to handle easier/shorter calls by telling you the reboot/unplug trick.

& if it works, then you both win! – tomByrer – 2013-07-29T19:42:10.040

3Often a reboot does work though. – TylerF – 2009-12-19T19:12:13.523

No doubt on that! – dag729 – 2009-12-19T20:42:28.240

2I hate it when I have to explain things to the support guy... I mean, I am calling them for help. And I often find myself having to help them figure out the problem I am having. Very annoying! – Svish – 2009-12-19T21:03:49.120

It's simple: capacitors last... And in some case more than 10 seconds. You must have heard from the cold boot attack, where they rely on just that feature of capacitors.

Tim

Posted 2009-12-19T11:27:39.393

Reputation: 243

@fixer1234 and RAM is essentially build from capacitors. – Tim – 2018-11-11T08:22:09.757