In a message dated 01/12/2000 5:36:48 PM Eastern Standard Time,
[log in to unmask] writes:

<<

 If you really wanna know, there are no filaments in
 monitors. They use a Cathode Ray Tube (CRT)
 powered by 30,000 volts to fire 3 Electron Guns
 on color models.
 Once a monitor has logged enough hours the CRT
 can crack from the heat and begin arcing and then
 there goes your flyback.

 just thought you should know
 -yui shin >>

Hi,
  As you point out, a monitor uses a Cathode Ray Tube. However, it has a
heated cathode (i.e. filament) to give off electrons, which are then
accelerated by the 30,000 volt supply, deflected by the deflection coils, and
hit the anode (the screen face, which is connected to the 30,000 volt
supply), this causes phosphors there to glow, and give off light. A color
picture tube has 3 guns, each with a filament (red, green, and blue), except
the Trinitron, which uses a single gun to do color.
  A cold cathode can function in an arc type device (i.e. a fluorescent
light, which is under a partial vacuum, filled with a gas), but a picture
tube is under a full vacuum, and does not work on this principle, and thus
needs a heated cathode to give off enough electrons to work. This is why it
takes a few seconds (5-15) for the picture on a monitor to appear from a cold
start. The cathodes (filaments) are warming up, and until warm, not enough
electrons are given off to excite the phosphors to give off light, and
therefore a picture. If you look at the neck of an operating picture tube,
you can see the filaments glowing red. Advances in cathode technology have
lowered the operating temperature of the filament (and increased its life),
but it still needs to be heated to operate.
  While it is possible for the glass in the picture tube to crack after
extended use, the most common failure scenario for high voltage arcing and
subsequent flyback transformer demise is due to insulation breakdown, either
in the transformer itself, the high voltage lead going from it to the picture
tube, or across dust and dirt buildup on the back of the picture tube
(especially when it becomes damp or moist).

Just my .02 worth,
Peter Hogan
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