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CRTs, or Cathode Ray Tubes, operate at very high voltages (some in the range of +50,000VDC). This voltage is required for the CRT to form a picture on the screen of your monitor. Even with the power turned off and the plug removed from the wall outlet, the CRT can retain these high voltages for a while.

When working on a monitor or television, you will need to avoid the heavy wire going to the side of the CRT. This is the wire that supplies the high voltage from the flyback transformer to the CRT. It is generally suggested that you discharge the voltage before working on the monitor or TV. Note that you must have the unit unplugged from the wall outlet.

To discharge the CRT:

  1. Either purchase a shorting probe or make one. If this is not an option, use two well-insulated screwdrivers.
  2. If using a probe, connect the wire and clip to the metal chassis surrounding the CRT. If using screwdrivers, place the end on one screwdriver on the metal chassis surrounding the fromt of the tube.
  3. NOTE: Make absolutely sure that you are not touching any metal parts during the next steps.
  4. If using screwdrivers, slip the end of the other screwdriver under the protective rubber grommet on the side of the CRT, where the high-voltage wire is attached to the tube.
  5. Note: When you discharge the tube, there may be a very bright flash and a loud snapping noise. Try not to look at the point where the flash will appear. Also, be aware of the snapping noise, as it may cause you to jump.
  6. Now, either slip the end of the shorting probe under the rubber grommet or cross the two screwdrivers together to create a path for the electricity to arc across.
  7. Remove the screwdrivers or probe.

Note that this just removes the high voltage at the CRT. There can still be large voltages on the motherboard in the CRT, especially around the large filter capacitors. Also, avoid the area around the fuses.

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