45

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?
Sathyajith Bhat
  • 61,800
Svish
  • 39,580

5 Answers5

63

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
  • 23,383
  • 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 Dec 19 '09 at 11:49
  • @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 Dec 19 '09 at 15:35
  • 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 Dec 20 '09 at 15:22
  • 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 Dec 20 '09 at 15:47
  • 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 Dec 21 '09 at 13:23
  • 2
    As 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 Dec 21 '09 at 13:27
  • 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 Dec 21 '09 at 13:38
  • 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 Dec 23 '09 at 15:38
  • 2
    I'd guess this does much the same thing - plus holding down the button makes sure you spend a bit of time waiting! – Phoshi Dec 23 '09 at 16:05
  • http://superuser.com/questions/27229/ethernet-port-troubles/27266#27266

    It is by far just a myth!

     – DHayes Dec 29 '09 at 20:24
  • I'd say more of a legend. It has elements of truth in it. – Phoshi Dec 29 '09 at 21:20
8

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
  • 480,290
  • 25
    More 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 Dec 19 '09 at 17:49
  • Reverse your ethernet cable... hehe, that's brilliant :p – Svish Dec 19 '09 at 21:01
  • 2
    Reversing 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 Jan 19 '15 at 19:26
4

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.

Radu Murzea
  • 327
MyDWing
  • 41
3

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
  • 1,934
  • 3
    Often a reboot does work though. – TylerF Dec 19 '09 at 19:12
  • No doubt on that! – dag729 Dec 19 '09 at 20:42
  • 2
    I 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 Dec 19 '09 at 21:03
  • 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 Jul 29 '13 at 19:42
1

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
  • 1,223