imac 27' i5 sparking not sleeping and buzzing!

Discussion in 'Mac Basics and Help' started by keebs1978, Feb 8, 2010.

  1. keebs1978 macrumors newbie

    Feb 8, 2010
    hello all im very new to forums so please go easy on me and what makes it worse im very new to apple to.
    i have recently purchased a 27" i5 imac less than 2 mths ago, the start of my problems was i turn the machine off one night and i could still hear a buzzing noise ( like a transformer on a power supply, im an electrician and that best describes it!) i ignored it to begin with and some days later when i could still here it thats when i got concerned, so i decided to unplug everything and restart, thats when problem 2 showed itself when i plugged any powered device into the usb ports got got blue sparks! (im no genius but that surely isn't normal, is it?) so i got on the phone to apple and after some button pushing they asked me to take it somewhere for repair, which i did and 2 wks later it returned with a new logic board and psu??? and still sparking! also i have read on a few posts that some imacs wont wake up for sleep, mines the complete opposite it wont sleep from either the menu or tapping the power button the only way i managed to make it sleep was to unplug ALL of the usb devices including keyboard and then tap the power and it slept like a baby! having spoke again with apple for a long time they now have agreed to exchange it (in a months time due to "no stock" on the applestore so really what im asking of you guys is have any of you heard of any of the faults listed
    1 sparks from usb when powered devices are plugged in
    2 buzzing noise when imac is turned off
    3 imac NOT sleeping

    is there any thing you would suggest many thanks keebs1978
  2. Makosuke macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA
    No. A USB device should never spark visibly under any circumstances so far as I know. It's only 5V and the current limit is supposed to be 0.5A, which I don't think is even capable of producing a visible spark even if you were trying. There's almost certainly something drastically wrong that has maybe the case's ground sitting at a much-too-high voltage.

    You said you're an electrician, so you might for the heck of it put a voltmeter between something metal on the case (theoretically that should be the same as the outside shield of a USB connector, I think) and the cable on the powered device(s) causing the spark. I'm gonna guess you see something substantial there. (I had a failing VCR with the case sitting at 50V AC once, which you could actually feel when you touched it.)

    One would assume the reason only powered devices do it is that they're grounded through their own power brick. Again, since you're an electrician, I seriously doubt this is the issue, but there's a tiny chance something like that could be caused by some sort of short or incorrect wiring in the house's wiring--I saw that happen with a building that was wired so that the "ground" line on the outlets was an out-of-phase hot. That caused some damage...

    Just to ask, though, have you tried carrying it to somebody else's house and plugging it in there, just to confirm that it does the same thing? Seems like the Apple repair folks would have noticed the behavior if it was doing it after they "fixed" it.

    It's possible that the power supply could make a VERY quiet buzz when the computer is off, but mine makes no noise I can detect, and I expect it's directly related to whatever short is causing the other problems.

    Given your description of the symptoms, it's a malfunctioning USB device keeping the computer from sleeping (this is standard with any USB device that keeps "prodding" the computer), which I'm going to guess is directly related to the severe power problems. Were it only one particular USB device and/or you weren't having the other issues, I might suspect the device or something else, but as-is, almost certainly faulty hardware.

    As for recommendations, get Apple to replace it, like you're already doing, and I wouldn't even turn it on for fear of killing my USB devices. If you do, I'd also shut down and unplug it before walking away, so as not to burn your house down.
  3. keebs1978 thread starter macrumors newbie

    Feb 8, 2010
    thanks for the info, just to let you know i have checked all earthing polarity etc in my house to no avail. also i have noticed that hot plugging the usb cable at the usb device end causes no sparks whatsoever??? its just at the back of the screen, will take your adice and unplugg every thing in the mean time and i guess just wait for apple to sort me. i havent had a chance to take it else where yet to try it but am heading to friends over the weekend may take it there(just a 27" screen its the easiest to transport around!) but again i cant see how it can be here as i have loads of gadgets i.e ps3, freesat laptops (sounds like a shopping list for me to get robbed!) all with usb and all with no sparks many thanks again keebs

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