Why the screen Shaking

If the picture is actually shaking or moving around on a CRT, I’d first check whether there’s a magnetic field near the TV. Speakers, power adapters, other electronics, or even another CRT nearby can cause the image to wobble or distort.

If nothing nearby is causing it, the problem could be inside the TV, such as a failing power supply, bad capacitors, or an issue with the deflection circuitry. I wouldn’t open the CRT unless you know what you’re doing, since they can hold dangerous high voltage even when unplugged.