[ale] OT: Question regarding whining monitors (for you EEs out there)

James P. Kinney III jkinney at localnetsolutions.com
Mon Mar 21 10:58:30 EST 2005


On Mon, 2005-03-21 at 10:36 -0500, dale.h at wa4dsy.net wrote:
> On Monday 21 March 2005 09:57, James P. Kinney III wrote:
> > On Sun, 2005-03-20 at 23:47 -0500, Jeff Hubbs wrote:
> > > Bad flyback transformer?
> > 
> > Nah. Transformers don't run at high frequecies. It is likely a bad
> > capacitor about to blow.
> 
> Exactly what a Comp USA tech would say ;-)
> 
> But seriously, Flyback transformers DO run at high frequencies - like 15.75 khz
> in TV sets.  Also, capacitors do not make noise.

Yep. My mistake. Flyback transformers do run in the low kHz range. If
they are whining, there is physical motion happening somewhere that is
making sound. In general, that is not good. The normal 60 Hz hum is
tolerable by touch. There should be nothing audible.

Capacitors do not make noise under normal operating conditions. However,
one that is about to fail can physically flex the walls and/or end of
the can and make it whine. Many transistors can also whine under powerup
stress. I'm one of the (un)lucky few who can hear electronic equipment
turning on.  Most systems work with harmonics that are out of the normal
hearing range. Some systems have very high frequency sound output. Watch
the dog next time the laptop is turned on and see if his ears twitch and
stay up a second or so after the power switch click. :)
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James P. Kinney III          \Changing the mobile computing world/
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GPG ID: 829C6CA7 James P. Kinney III (M.S. Physics)
<jkinney at localnetsolutions.com>
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