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Originally Posted by Al Skierkiewicz
James,
I work with a man who worked at Sony for many years and this is his opinion...
The high resolution Trinitron tube has a very fine shadow mask to match the small phosphor stripes on the front of the tube. The electrons from the three color guns pass through the slots in the shadow mask at different angles to energize the three color phosphors printed on the inside of the faceplate. The shadow mask is so fine that changes in temperature were affecting the beam landing so Sony introduced a support structure that compensated for the temperature and supported the very fine mask. Those are the two fine black lines you see running horizontally at about a third and two thirds of the screen height. The metal parts of the picture tube are affected by magnetic fields like speaker magnets and the earth's magnetic field. There is a degaussing coil built around the picture tube that generates a moving and variable intesity field, at turn on, that is supposed to erase the magnetic field taken on by the metal parts. What we feel has taken place is the magnet you applied has generated such a strong field, the degaussing coil cannot overcome it. There are coils that are used by service people that can erase this field. What we think is occuring is that the magnetic field on the shadow mask is causing the electrons to strike the black stripes between the color phosphors on the faceplate of the tube and that is what is causing the black vertical strips. If you look close, you should see the there is faint color at the very edges of the black lines. If this is the case, you need to see if you can borrow one of the service deguassing coils or take it to a TV shop and let them try to deguass it.
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Hmm sounds possible(from my limited understanding of CRTs). Its seems to me that if the shadow mask were this magnetized, the colors would be distorted. I don't have access ot a degaussing coil, and i don't feel like payign for somethign soo simple. From my understanding, a degaussing coil is nothign more than a big 60hz electromagnet that plugs into the wall. Anybody know how many turns of what radius i need to build one?
I just realized somehting about the vibrating patterns when i hit the screen. Its not the actual lines that are moving, but rather it seems they are casting phantom vibrating lines beside themselves. Also, Its hard to tell, but some of the lines do seem to have colors bordering them.