dust patterns on CRTs

[CTho9305]

I was looking at my TV and noticed that dust was not all over the screen. The corners had no dust at all - the dusty area was like a rounded rectangle. The dusty area did not cover all the area where there was picture.

Is the screen not evenly charged? Why?

Maybe I should clean it occasionally 😀

 

[Agent004]

Sometimes the screen doesn't charge evenly, since the screen is a bad/non conductor so the electrons can't free distribute themselves.

Also you got to think about the physcial geometry of the screen, sometime it seems flat but actually it's not, with the middle part been the 'outer' most and the corner(since it's where the screen is mounted) been the most inners part.

The 'gun' inside the tv isn't as accurate as you think, with the corners been the hardest to reach (at certain angle ), not like the centre most part which is just straight ahead.

 

[CTho9305]

drawing. imagine that is the TV screen. outside the lines is no dust, inside is dust. why would proximity to the electron gun result in less charge?

 

[Bozz]

I honestly dont know the answer to your question but i'll speculate - Is your TV's cabinet made of plastic? The front surface of the CRT is non conductive however when you initially switch on the television, the inside of the tube between the viewable front and up to the deflection yoke is covered in conductive material (as is the outside) which creates a large capacitor. This area is called the Aquadag (funny name, i know 🙂 ). One thing I've found from years of television servicing/repairs is that dust tends to attract itself far more around the EHT plug/socket of the tube, there's about a 5" radius from where the socket is to where the external conductor of the aquadag is. Since the inside charges to approximately 26KV and the outside is connected to the chassis earth, I simply assume the area where the aquadag is not coated on the outside of the CRT to have an unshielded 26KV DC attraction to dust...

How does this apply to your situation?

I reckon that the static electricity buildup on the surface of the front of the CRT is higher in the centre of the CRT because the CRT is mounted with four metal bolts/screws to the plastic cabinet in all four corners. The corners may have a lower static charge due to being connected to the cabinet.

That's my guess, do not hold me responsible as to the accuracy 🙂

 

[CTho9305]

Originally posted by: Bozz
...
That's my guess, do not hold me responsible as to the accuracy 🙂

you lost me 🙂

maybe i'll do what other civilizations/religions would do: declare a dust god that chooses to not dust the corners of CRTs 😀

 

[Agent004]

Originally posted by: CTho9305
drawing. imagine that is the TV screen. outside the lines is no dust, inside is dust. why would proximity to the electron gun result in less charge?

Like I said, the gun isn't as accurate as you think, it's less accurate -> less chance of electron (correct me if I am wrong, it's been some time I deal with CRT) hitting the desire postion. Hence the misplaced electrons will build up the charge else where and less charge on the corners (since it couldn't distribute itself in a bad/non conductor).

 

[Howard]

Could somebody with an LG Flatron monitor check out their dust patterns? I think I've got a theory.

 

[CTho9305]

Originally posted by: Yucky
Could somebody with an LG Flatron monitor check out their dust patterns? I think I've got a theory.

I would imagine most people clean computer monitors - i can't stand any dust on my computer screen.... unlike the TV 😉

 

[Flyingcool]

dust sucks, I have to clean my TV every week with a wet nap