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I've got a nearly 3-year-old MacBook Pro 15" 2.16GHz (MacBookPro2,2). When I am not using the extended, grounded adapter for the power supply, just using the simple, two-prong plug, I can hear a buzzing when I use very sensitive earbuds. This goes away if I touch a metal part of the laptop.

Also, I can feel a weird, fuzzy feeling when I brush the metal parts of the laptop lightly with my fingers/skin. Somewhat similar to feeling of a touching hair or a balloon that's charged with static electricity. But I'm not getting sparks or anything. And if I'm touching a metal part of my laptop solidly (not just brushing it) and then I touch someone else's skin I can feel the same effect and so can my victim.

I've noticed similar effects with an ungrounded electric blanket. But with that the buzzing can be easily heard without headphones.

Is this a defect, normal, or something else? And what exactly is happening?

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What happens with the laptop is running just on batteries and not plugged into a LAN cable, PSU or anything else? Do you still get the effects? –  Matthew Lock Feb 1 '10 at 3:37
    
Nope. There are no problems just running on battery. –  donut Feb 2 '10 at 6:07
    
My ipod touch (the one with the aluminium back) does the same thing when it is plugged into the charger. I just figured apple failed at grounding it correctly. –  Jamie Penney May 9 '11 at 1:11
    
Related question and answer: apple.stackexchange.com/questions/10545/… –  Memming Jul 14 '13 at 18:10
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5 Answers

up vote 4 down vote accepted

I am an electronic engineer, living in Korea, and thought I don't have/own a Mac, I use a number of USA electroinc items in my electronics lab. I have indeed seen this problem frequently. I'm not a power supply expert, but it appears to be related to the way 220V outlets are powered here versus how they are powered in the USA. Here, one of the two "hot" prongs is actually a neutral (nominally at ground potential), just like our 110V outlets in the USA. In the USA, however, our 220V outlets both prongs are "hot", neither one is at ground potential.

I haven't worked out in my mind exactly what's going on. Without getting deeper into circuit design theory, the fundamental problem is that the power supply, having no ground reference. has to guess where ground should be for the DC output. Some do a better job than others. I've measured supplies whose outputs floated from 30 to 90 volts above ground. In most of these cases, the extra voltage was enough to prevent other connected equipment from working, and often enough to "feel", as you are feeling on your laptop.

I would recommend finding any buying a three-prong, grounded third-party power supply. It's unbelieveable that the manufacturer would just say "oh, that's normal". Yikes!

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The manufacturer didn't say that, a third-party Apple authorized dealer in Korea said that. The adapter Apple sells for Korea is only 2 prong. But it does have a three prong US adapter but I haven't seen a three prong US to Korea adapter yet. I'll look harder next time I'm in Korea. And thank you for explaining more about this, I really appreciate it. –  donut May 23 '11 at 3:57
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This is NOT normal. It sounds like a wiring fault somewhere.

You shouldn't be using ungrounded 'two-prong' plugs.

Have it checked by a qualified person.

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The power supplies for Macbooks come with two prong and a (extended) 3 prong adapter. So my guess is that it should normally be okay. I've used other laptops as well with only 2 prong adapters (for use in other countries) and have had no troubles. –  donut Jan 26 '10 at 8:15
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Likely to be a fault in the power adapter. Try a different one if you can, or at least only use the laptop when not charging it. –  Martin Jan 26 '10 at 8:26
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Yes, the third GROUND pin isn't essential in a properly wired appliance, but it's a good idea and causes some wiring errors to blow fuses when they would otherwise go unnoticed (or perhaps cause 'weird sensations') –  pavium Jan 26 '10 at 8:45
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I got a new charger and this happened. So I returned the charger and got another and the problem went away. –  mechko Feb 28 '10 at 20:04
    
It sounds as if a very high-voltage, high-frequency, low-amp current is being conducted by the aluminum shell. I wonder if the MacBook uses the shell as a ground for its circuits, similar to the way cars use the body as a ground. –  CarlF Sep 1 '10 at 18:43
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So, I went to a reputable authorized Apple service center here in Korea and they basically said that this is normal and happens with every ungrounded, aluminum bodied Macbook. I was able to feel the effect with other laptops in the store. I'm currently living in Korea. I don't think Apple manufactures a grounded plug adapter for their external power supplies for Korean plugs. Really, it only seems that in the last two years that Apple has really regarded Korea seriously, so maybe they'll come soon.

I guess that's that. I'd still like to hear an explanation for what's creating this effect. Also, they said that some people can feel it more than others.

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So you're shocked any time you use your Mac? That is both weird and troubling. –  alex Feb 1 '10 at 11:42
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Not shocked, at least I don't think. Just a very light almost fuzzy feeling. I really don't know how to describe it accurately. –  donut Feb 2 '10 at 6:08
    
Never been there, but the internet just told me that these are the only grounded outlets in use in South Korea, and they don't seem to be exceedingly common: electricaloutlet.org/type-f –  Hasaan Chop Mar 21 '10 at 5:00
    
Actually, most wall outlets and many power strip outlets are grounded. But yeah, in the world they are not that common. I guess that's what you mean and Apple doesn't make a grounded adapter for their power supplies. –  donut Mar 21 '10 at 11:04
    
There's another good description of the effect here: boards.straightdope.com/sdmb/showthread.php?t=592727 I have two power supplies - one mac, one cheapo aftermarket. I only get the effect with the latter one. –  Steve Bennett Dec 15 '11 at 23:23
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I have the unibody aluminum Macbook too and the same thing happens to me when I have the adapter plugged in w/ the two prong Macbook charger. Youre not getting shocked but you can feel the current if you slide your finger on the body of the laptop while it's charging. Its very odd and I agree it should not be happening. My Macbook is about 1 1/2 years old. It was the first unibody aluminum laptop and I noticed that this was happening about 6 months ago.

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It's weird, but apparently this is normal. At least it seems all the aluminum bodied Apple laptops do this when not grounded (using the 2-prong adapter). Wish I could get a clear answer from someone on what is causing this sensation. –  donut Mar 21 '10 at 11:05
    
That's not current you're "feeling", it's the Macbook vibrating. –  user47585 Feb 7 '13 at 0:54
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You are getting AC current on the negative DC pin out from your charger.

This is not normal and is a serious risk to your safety, it can cause damage to other items when you connect them (wired) if the conditions are right. The feeling you describe is an AC cycle with 60 Hz or 50 Hz and if you ever feel that then it's potentially lethal in the right combination of circumstances.

I suspect a large batch of faulty cheap design AC adaptors are to blame. Contact your electrical standards board for your country to confirm this, they will want to test the adaptor themselves.

This is a clear violation of electrical industry standards and is not "normal" by any means. It means the AC is leaking into the negative of the supply and making metal ground parts potentially lethal.

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