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Old Jan 21, 2013, 12:29 PM   #1
PavelT
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2012 iMac still on, even when shut down?

when i shut down the new 2012 imac. i still hear a electrical current /frequency inside of it. the same frequency sound it makes when it is on. if i unplug it from the wall outlet, it stops of course. it also stops when its been turned off for several hours...also i do have a external usb 3.0 hd plugged in at all times, But when i unplug it, noise is still there...any thoughts? thanks.

note: the electrical buzzing noise is present whether computer is on or off, just as long as it is plugged in.

Last edited by PavelT; Feb 10, 2013 at 08:52 PM.
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Old Jan 21, 2013, 01:37 PM   #2
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How are you shutting it down? If you are using the power button on the back, you may have the System Preferences set to simply put the computer to "sleep" rather than totally shutting down. That may also explain the delay as it goes from "sleep" to "deep sleep" after a period of time (do iMacs do this like laptops do?).

It may be the fan on idle.

Use the "AppleLogo/ShutDown" in the upper left corner to really shut it down ... or change your settings if you like to use the power switch.


If that doesn't work ... it may be the ghost!

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Old Jan 21, 2013, 01:57 PM   #3
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any thoughts? thanks.
Every modern computer is still on even when 'powered off', you have to yank out the plug to turn them of completely

Anyway, your iMac shouldn't output any hearable noise when turned off. This suggest a faulty capacitor or such. I'd return it if still possible or at least tell Apple about it.
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Old Jan 21, 2013, 02:35 PM   #4
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How are you shutting it down? If you are using the power button on the back, you may have the System Preferences set to simply put the computer to "sleep" rather than totally shutting down. That may also explain the delay as it goes from "sleep" to "deep sleep" after a period of time (do iMacs do this like laptops do?).

It may be the fan on idle.

Use the "AppleLogo/ShutDown" in the upper left corner to really shut it down ... or change your settings if you like to use the power switch.


If that doesn't work ... it may be the ghost!
i use the normal "AppleLogo/ShutDown" method to shut it down. always.
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Old Jan 21, 2013, 02:53 PM   #5
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Lightbulb Maybe I am way off here...

...but I have a Powermac G4 MDD that also makes noise when it is off (not sleeping!)

Because I regulary open it up to do things inside (ad memory change HD and so on), I stumbled upon the cause in my case by coincidence

... the main fan was running (at low rpm) although the machine was off?!

After a while and some plugging and unplugging I found the cause;
I have a Kensington 7 port powered USB hub and this hub mysteriously 'injects' power into the mac causing the main fan (controlled by the motherboard) to run as if it was powered with 5 Vdc.
Now let that be the voltage on an USB bus by coincidence...

As I said, maybe the cause is entirely different in your case...
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Old Jan 21, 2013, 02:58 PM   #6
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The iMac's +5 volt standby power is always on as long as it's connected to AC power. The buzz you hear is from the voltage inverter.
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Old Jan 21, 2013, 09:40 PM   #7
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The iMac's +5 volt standby power is always on as long as it's connected to AC power. The buzz you hear is from the voltage inverter.
so you are saying because it is plugged in, it always has buzzing current, that i am hearing. i never experianced this with previous macs...is this a mountain lion thing?
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Old Jan 21, 2013, 10:27 PM   #8
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so you are saying because it is plugged in, it always has buzzing current, that i am hearing. i never experianced this with previous macs...is this a mountain lion thing?
It has nothing to do with the OS, it's just a matter of tolerances in the power supply components, usually the power inverter coils. It might just be one coil that's slightly looser in either winding, or mounting on the circuit board. It has no bearing on the operation, or reliability of the power supply. Some Macs produce varying buzzes from the LED control circuits depending on the screen brightness settings, basically due to the same effects.

Old CRT TVs used to produce audible buzzes or whines from the high voltage power supply or deflection coils.
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Old Jan 22, 2013, 03:59 AM   #9
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If I put my ear to the top right of my iMac when it's running, I can definitely hear a very, very slight electrical current/line in the system. I have to have my ear to it, though.

When the system is powered off, though, I don't hear any electrical noise at all. Not sure why you'd be hearing anything with the system off. How's the power in your house? Are you using a line conditioner of any sort, or a UPS?
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Old Jan 22, 2013, 09:12 AM   #10
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so you are saying because it is plugged in, it always has buzzing current, that i am hearing. i never experianced this with previous macs...is this a mountain lion thing?
I have an audio engineer friend who can hear things I can't. You may be one of those who can hear certain frequencies and the new iMac falls into "your" range. But if friends/family can hear it too, maybe you have a sick component.

Also, have you tried plugging into a newer power strip/protector and/or wall outlet? Any change?
Additionally, try a test with unplugging your external drives before power down, but try these two things one at a time.

My iMac has a very slight sound when in sleep mode but not when off.
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Old Jan 22, 2013, 09:13 AM   #11
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Power Nap?
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Old Jan 22, 2013, 09:30 AM   #12
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It really bugs me that APple didn't put a small power on light on the front somewhere. I'm always not 100% sure if the unit is powered on or off fully. I can't imagine what they were thinking.
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Old Jan 22, 2013, 01:12 PM   #13
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It really bugs me that APple didn't put a small power on light on the front somewhere. I'm always not 100% sure if the unit is powered on or off fully. I can't imagine what they were thinking.
I am 100% against any lights on the front of my iMac. Yuck! So distracting.
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Old Jan 22, 2013, 05:43 PM   #14
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Power Nap?
Sadly, no power nap on iMacs.
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Old Jan 23, 2013, 12:09 AM   #15
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Also, have you tried plugging into a newer power strip/protector and/or wall outlet? Any change?
Additionally, try a test with unplugging your external drives before power down, but try these two things one at a time.
my set up is that, i have a late2012 27inch, with an external ssd running the osx on it via usb3, the internal hdd is wiped blank (i just use it for empty storage space).

now, it makes a buzzing/electrical current sound when it is on (sound varies sometimes louder, and at times very quiet), i figure that part is normal?..but that sound continues when it is shut down..there is definitely current in there when its shut down.

i have tried switching outlets, extension strips, etc and it still has that buzzing current when its turned off. as soon as imac plugged in, the noise appears...unless it has been off for several hours, then the noise is gone.

i shut mac down and removed my usb3 ssd external boot drive after and noise it still there.

i powererd the mac without my ssd external os plugged in, and then shut it down (because there is no osx elsehwere, simply speaking) and the noise is still there.

anybody else notice this on their imac? suggestions?
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Old Jan 23, 2013, 02:28 AM   #16
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PavelT, that's odd. Sorry I can't offer any other suggestions.
Might be worth a call to Apple support, so IF a component does go bad in a month or so, then they at least have you on file already.
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Old Jan 23, 2013, 01:51 PM   #17
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i called apple, have an appt with so-called genius bar, will let you guys know what they tell me. its just so odd....i suspect a faulty power supply.
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Old Jan 23, 2013, 05:35 PM   #18
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this may sound weird, or maybe not??...but i reset the v-ram, and the electrical buzzing is gone!...my genius bar appt isnt till end of the week, but i might end up canceling it....does this make any sense?
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Old Jan 23, 2013, 05:37 PM   #19
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If you're having weird problems like this already, I would definitely get it checked out by Apple.
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Old Jan 23, 2013, 10:12 PM   #20
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noise came back on. i am taking it to genius bar as planned....
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Old Jan 23, 2013, 10:25 PM   #21
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noise came back on. i am taking it to genius bar as planned....
I'd take the iMac to a friend's house to rule out the power in your house.. Or plug it into a UPS to test.
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Old Jan 23, 2013, 11:29 PM   #22
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I'd take the iMac to a friend's house to rule out the power in your house.. Or plug it into a UPS to test.
wouldnt using a surge protector rule out grouding/voltage issues from the home? i normally have it connected to a surge protector, but have also tried various wall outlets.. and the buzzing is in all of them. buzzing noise levels do vary from time to time.
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Old Jan 24, 2013, 12:07 AM   #23
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wouldnt using a surge protector rule out grouding/voltage issues from the home? i normally have it connected to a surge protector, but have also tried various wall outlets.. and the buzzing is in all of them. buzzing noise levels do vary from time to time.
It depends what kind of UPS you get.

The easiest way to make sure it's not your home power is to plug it in at a different location. It's odd that you're hearing any sound from an iMac that is powered off.. Very odd.

Given the backordered nature of your system, I'd try that just to be sure, even if it means bringing it to the Apple Store to test (assuming you can hear the noise in that environment).
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Old Jan 24, 2013, 05:57 PM   #24
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It depends what kind of UPS you get.

The easiest way to make sure it's not your home power is to plug it in at a different location. It's odd that you're hearing any sound from an iMac that is powered off.. Very odd.

Given the backordered nature of your system, I'd try that just to be sure, even if it means bringing it to the Apple Store to test (assuming you can hear the noise in that environment).
thanks. i took it to a friends house and the noise did not come in. but it didnt come in at my hosue either. its been quite all day today. last night was the last time the buzz came in. so my results are inconclusive...it comes in at random times. its best to bet, that when i take it into genius bar, the sound will probably not come in (unless it decides to) and the guy will dismiss any problems...thats my worry. or do they have other ways of checking it?..also i have the istat app. is there any ways to tell of voltage red flags on istat?
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Old Jan 24, 2013, 07:24 PM   #25
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thanks. i took it to a friends house and the noise did not come in. but it didnt come in at my hosue either. its been quite all day today. last night was the last time the buzz came in. so my results are inconclusive...it comes in at random times. its best to bet, that when i take it into genius bar, the sound will probably not come in (unless it decides to) and the guy will dismiss any problems...thats my worry. or do they have other ways of checking it?..also i have the istat app. is there any ways to tell of voltage red flags on istat?
If it's time-dependent, it may well be something to do with the power in your house. But obviously I can't prove it. That is very bizarre....

iStat Menus lists some voltages, but I'm going to bet yours are all within spec. I agree taking it into the Apple Store might be frustrating at best, given the intermittent nature of the issue.

Hmm... I'd just wait till it does it again and note the time it happens during the day, to see if it's anything to do with that...
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