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Thread: Why pull plug on power supply??

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  1. #1
    Join Date
    Nov 1999
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    Pittsburgh, Pennsylvania, USA.
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    Question Why pull plug on power supply??

    I just now finished making my own solution to the problem, BUT all the instructions I have read say before adding, removing or touching computer parts; turn off the PSU and unplug it!

    My concern has always been; if static discharge is a huge problem in handling computer parts, then why disconnect the PSU and the comp case from your ground source?

    I used to always use a wrist strap grounding device but I test it before use and when I found it to be defective I through it away.

    My new solution is that I got a four foot piece of heavy stranded wire and I put a small battery charger clip on one end and the other end is attached to the ground post in a replacement three prong electrical plug.

    Now, I clamp the one end to the case and plug the other end into my power strip or wall outlet and I can still do what the experts say and still feel comfortable that I can touch a real ground before touching my parts ( I mean my computer parts ).

    I'm assuming that even though I turn my PSU off that the experts still think that something is still on anyway!


    Wild Willy the Wacko

  2. #2
    Join Date
    May 2010
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    Simply shutting down the computer doesn't turn the power off. The power supply continues to provide a trickle (sometimes more than a trickle, depending on what all you have installed) of standby current to the motherboard. Not all power supplies have an actual on-off switch; it yours does, then switching it off actually disconnects the power - but likely only cuts the hot side of the line so the neutral is still connected, which is potentially unsafe if you get between that and a ground. Pulling the plug entirely (turn everything off, then just pull the IEC plug off the power supply) takes care of that problem, and if you don't have an actual switch on the p/s it also kills the standby power.

    For laptops, the equivalent is to disconnect any external power plug, then remove the battery.

    "Grounding" yourself to the chassis while messing with things inside minimizes the static potential between you and what's inside. It's not actually connecting to an earth ground. The chassis and what's inside of it, and you, may be (and probably are) at some potential to an earth ground, but that's not the concern - the issue is to prevent a static discharge through some semiconductor between you and the chassis. As long as you and the chassis are at the same potential it won't happen.
    Last edited by mikeebb; 07-16-2015 at 09:29 PM.

  3. #3
    Join Date
    Sep 2004
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    Marion, Iowa, USA.
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    Another thing to worry about is grounding to the house wiring ground, you can get feedback through the ground from other things in the house, this is known as stray voltage. It can get as high as the normal voltage in your home.

  4. #4

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    Not only should you unplug the cord, you should press the power button to discharge whatever might be left in the capacitors or you might give yourself one heck of a shock should you touch one.

  5. #5
    Join Date
    May 2010
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    Quote Originally Posted by Seluryar View Post
    Not only should you unplug the cord, you should press the power button to discharge whatever might be left in the capacitors or you might give yourself one heck of a shock should you touch one.
    Somebody with more hardware experience please correct me, but I don't think modern PC power supplies work that way. Nothing happens if you press the power button and no standby power is available, charged capacitors or not. Of course, most of us shouldn't be messing around inside the p/s cage where the big capacitors and line-voltage points are -- p/s is usually considered a non-repairable item so if you suspect it's bad you replace it as a unit. Still, you do need to isolate the chassis so you and it can be properly grounded to each other when working on other parts.
    Last edited by mikeebb; 07-18-2015 at 07:54 PM.

  6. #6

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    There are capacitors on most motherboards

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