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

[Calvin Harrigan]

James P. Kinney III wrote:

>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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The whinining is a physical noise in the flyback, yoke, or some other 
coil (typically used for pincushion correction).  Sometimes the noise is 
caused by  a loose
ferrite core or lamination in the these devices.  A lot more times you 
have a high voltage capacitor who's value is changing and causing the 
circuit to detune.  It will eventually get to a point where it will 
cause the wave form appied across/through the coils to distort and this 
distortion (noise) causes the device to vibrate.
Or something like that.

Calvin...