not 100% sure about the ms9, but if the ms8 (which is pretty close in design) is missing the 200v power supply off the flyback someplace that feeds power to the video amp circuit, they will do this. have to check the resistors and whatnot in that power supply rail to see if something has gone open. usually there is a broken solder joint or a blown open resistor near the flyback someplace.
if you do find an open or blown out resistor, be sure to replace it with the same type (IE metal oxide resistor or wire wound etc. they are often labeled "flameproof" resistors) or if it fails again, it will do so in a spectacular fiery fashion and will burn up so hot that they can quite literally burn your house down.