In a message dated 9/6/01 11:13:48 PM Eastern Daylight Time, [log in to unmask]
writes:


> Hi friends,
>
> when I switch my monitor on, it starts with a " twung  or Dung noise",
> little louder than the normal starting indication.
>   Can somebody please tell me what it is .Is it a signal for a future
> trouble ?
> Pl advise.
> Jagpal S.Tiwana
> Dartmouth, NS, Canada

Hi,
  Monitors (and TV's for that matter), have degaussing coils around the
picture tube, to remove any stray or residual magnetism in the tube, that can
affect the color of the picture. The circuit that operates them typically has
a thermistor in series with the coil.
  The thermistor has a low resistance when cold, and a much higher resistance
when warm. So when you first turn on the monitor, the cold thermistor lets a
lot of current flow through the degaussing coil, producing the noise you are
hearing (and degaussing the screen). The current flow heats the thermistor
up, causing its resistance to increase, and effectively shutting off the coil
after a few seconds (and it stays off as long as the monitor stays on).
  Then when the monitor gets turned off, the thermistor cools down, and the
cycle repeats the next time the monitor gets turned on.

HTH,
Peter Hogan
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