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Original post by rickwag,

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I worked on a lot of CRT screens back in the 80’s. That rubber cap on the back of the CRT is where the voltage from the fly back transformer comes in. WARNING: THIS VOLTAGE IS HIGH ENOUGH TO REACH OUT AND TOUCH YOU! Do not try to measure this voltage with a standard multi-meter; you have to have a special hi-voltage probe, which is long and insulated. That extremely hi voltage is needed to push the electron stream across the vacuum space in the CRT; I have seen in excess of 40KV on some systems. We used to use a long flat blade screwdriver with a ground cable attached. Push the screwdriver tip under the edge of the rubber cup, you may see a spark. Then it would be discharged. If you are disposing the CRT it should have the vacuum pressure released. To release the pressure there is a metal connector under the rubber cup. Once the CRT has been discharged, disconnect the connector under the rubber cup. You will see the little metal connector nub underneath. You can cut that with diagonal cutters and you will hear the vacuum hiss; that is air rushing in the CRT tube. After that you can safely break the back of the CRT tube if that is your plan.

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