Why is it that old CRT box TVs would be totally ruined by a decently strong magnet rubbed on the screen?
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Old CRT (Cathode Ray Tube) box TVs would be ruined by magnets because of the way the CRT technology works. Here’s why:
1. Electron Beam and Magnetic Fields
In a CRT TV, the display works by firing an electron beam at the phosphor-coated screen. The phosphor lights up when hit by electrons, creating the image you see on the screen. This electron beam is precisely controlled by magnetic fields created by coils inside the TV.
- The electron gun emits a beam of electrons that is directed towards the screen.
- To properly direct the beam, the TV uses magnetic deflection. The horizontal and vertical deflection coils inside the TV use magnetic fields to guide the electron beam to specific points on the screen, creating an image by lighting up the phosphors in the right spots.
2. The Effect of an External Magnet
When a strong magnet is introduced near the screen, it disturbs the precise magnetic fields controlling the electron beam. This interference causes the electron beam to be misdirected, leading to various issues:
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Color distortion: The electron beam, which is responsible for the color and brightness of the image, can be altered by the external magnet, causing color bleeding, warped images, or distorted colors on the screen. This is because the magnetic field from the magnet would pull the beam off its correct trajectory.
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Permanent damage: In some cases, if the magnet is strong enough and held in place for a long period of time, it could cause permanent degaussing or even damage to the CRT's components. The screen itself could become permanently distorted, with patches of discoloration that would not go away.
3. Degaussing:
Older CRTs were equipped with a degaussing coil to counteract the magnetic field buildup from environmental sources (like nearby speakers or electronics). However, a strong external magnet could overwhelm the degaussing coil's ability to correct the interference, leading to permanent color distortion.
4. CRT Technology and the Risk of Magnets
- Magnetic fields are essential to the functioning of the CRT, but when they are disrupted by an external magnet, it can lead to irreversible changes in the display's ability to show a clear image.
- Over time, if a magnet was constantly rubbed on the screen, the image quality would degrade dramatically.
Conclusion
In essence, old CRT TVs were highly sensitive to external magnetic fields because of their reliance on precise magnetic deflection to guide the electron beam. A strong magnet could interfere with this process, causing color distortions, misalignment, or even permanent damage to the TV. This was one of the reasons why magnets were considered dangerous to CRT displays.