The cathode ray tube is a giant capacitor. During operation it is charged to 20+ kilovolts, and it takes a long time to discharge even after being unplugged fr

The cathode ray tube is a giant capacitor. During operation it is charged to 20+ kilovolts, and it takes a long time to discharge even after being unplugged from the wall. (Some but by no means all TVs have a circuit which discharges the tube). There are also large capacitors in the power supply which maintain hundreds of volts even after being unplugged. When the TV is connected to power, the flyback transformer (a large circular device soldered to the main board) generates a range of voltages from hundreds up to 20+ kV which are wired to various parts of the tube. Some of these are present on the neck board which is exposed at the pointy end of the tube. US TVs are extra spicy because they sometimes have no earth, so if the power is wired backwards (either in the plug or more insidiously from the wall), everything metal inside the set can be live. If you overvolt the tube (a worry with this replacement board actually) then it can emit x-rays. Most "modern" CRT main boards have a circuit which detects this, but maybe older ones or cheap knock-offs don't. In short, if you don't know what you're doing, stay away.