linux-kernel - Re: PROBLEM: MacBook makes whining noise when usb-uhci active

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Date:	Sun, 8 Jul 2007 13:58:14 +0200
From:	Carlo Wood <carlo@...noe.com>
To:	Tim Hull <thully@...ch.edu>
Cc:	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Gerald Britton <gbritton@...mcom.org>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-kernel@...r.kernel.org
Subject: Re: PROBLEM: MacBook makes whining noise when usb-uhci active

On Sun, Jul 08, 2007 at 12:41:55AM -0400, Tim Hull wrote:
> After reading the ThinkPad wiki link, I've found that the problem has
> to do with the C3 and C4 ACPI states.  I'm guessing that the 2.6.18
> kernel I was using on Debian Etch just happened to not support full
> power management on my MacBook - hence, the problem didn't occur.
> 
> Sorry for all of this - I guess I'll pass this info on to Apple and
> see if they may be able to fix this with a firmware update (it occurs
> on OS X too).

The most likely source of a noise as you seem to describe is a
ceramic capacitor. An alternative is some coil, but that you
usually only hear in cases where a high frequency is used inside
a voltage convertor (in order to reduce transformator or coil
sizes) and I doubt that anything like that is possible in a
laptop... I'd have the hear the actual sound to know what it is.
99% chance it's a ceramic capacitor that has to absorb some
pulsed current.

If you'd replace the capacitor with another one of a different
type (same capacity, of course), for example a styroflex one,
then the noise would go away. It's very difficult to find out
which it is however ;). The only method that I know is by
touching each capacitor (ie with pliers) while it is making noise,
which will cause the sound to change a little if you have the
right one.

-- 
Carlo Wood <carlo@...noe.com>
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