aluminum powerbook and a possible electrical issue

Discussion in 'PowerPC Macs' started by TESEV, Mar 17, 2008.

  1. TESEV macrumors member


    Jun 1, 2006
    New Orleans, LA
    File this under "I have a bad feeling about...". So whenever I am on a landline phone and I have my PowerBook G4 (aluminum) sitting on my lap, I hear this obnoxious buzzing sound coming from the phone. When I take my PowerBook off of my lap the buzzing stops. I suspect this is a grounding issue because I have a 3rd party AC adapter that doesn't have a grounding pin. I used to have an Apple adapter with the pin until I destroyed it (and I think an Apple replacement is ludicrously expensive (and no, the warranty expired 2.5 years ago)).

    I'm no electrical expert, but I'm not comfortable with what I'm hearing. Am I being paranoid or....?
  2. idonotliketostu macrumors 6502

    Feb 28, 2008
    Did you try it with the powercord not pluged in?

    Maybe the magnetic field generated by the cord is messing with the magnet in the phone.

    I think its probably more to do with the wifi signals than anything else.

    Maybe not.
  3. TESEV thread starter macrumors member


    Jun 1, 2006
    New Orleans, LA
    I never had the problem with the Apple adapter; I think it was because it had a grounding pin.
  4. PeterC-7 macrumors member

    Jan 30, 2008
    This sounds like an earthing/grounding issue I've had for years going right back to my Tibook.

    The metal skin is earthed back to the power-supply but if you don't have a grounded plug - 3 pin - it stops there. When you touch the metal skin and touch the ground with your feet, it earths through you.

    I used to work on a concrete floor with bare feet and had constant trouble with pin-prick, high-tension/low amp shocks when sensitive underside of my forearms rested on the front corner of the TiBook.

    The Powerbooks had the same problem and I'm suspecting the MBP's do too.

    As far as I know, since only low voltage DC goes to the laptop, there is no danger of lethal shock. I think there must be some sort of electrical energy being carried by the metal outer skin, because - on my PB's at least - if you had a non-earthed plug and were earthed yourself, you could feel the same sort of slight stickiness on its surface that you get on a touch-activated table-lamp. The stickiness disappeared when the power-supply was earthed.

    It still concerns me that this type of emission can be sitting on my lap - or close to it.
  5. DOBM macrumors newbie

    Aug 8, 2008
    Earth problems

    Hello, I suspect the buzzing noise is indeed an earthing issue. I have a MacBook Pro (2008 latest model) and was using this in my car attached to a Kensington power inverter. All was powered and working, but I was getting a buzzing noise from...

    the end of my elbow!

    Which was resting against a rubber strip between the door and window.

    When I removed my elbow, the buzzing stopped and when I touched the strip I received an electric shock.

    After a bit of research and testing I discovered that the 'long' mains lead which plugs into the Apple PSU DOES have an earth connection to the PSU from the 13A plug, however, the little Mac 'Travel Plug' which connects to the same place on the PSU, does NOT have an earth connection.

    Using the travel plug means that the voltage to the MacBook 'floats'. Any extraneous voltage often caused by spikes, which are near impossible to measure, (a DVM is far too slow) are leaked through the chassis of the laptop and then through you!

    Using the long mains cable with an earth resolves the problem, the 'leak' goes to earth not you.

    I spoke with Apple support and they do not make an earthed travel plug which I find rather odd really.

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