Composite Black and White monitor dead

You were somewhat lucky. Sometimes the horizotnal output transsitor just fials (as yours did), but sometimes it's killed by some other fault (shorted turned in the flyback transoformer being the worst, but shorted/leaky diodes and capacitors in that circuit can do it too). I haev learnt by bitter experience to always order a few spare transistors when fixing this kind of fault in case the new one fails instantly at switch-on. Worse still is when there's a fault component i nthe drive circuit, often a capacitor in the base netowrk of the horizotnal output tranistor itself. If this causes the transistor to swtich more slowly, then said transistor will dissipate more power (think about it like this : If the transisotr is staturated, the volage across is it low, so it doesn't dissipate much power. If it's cut off, it's passing next-to-no current, so again the power dissipated is low. But between those states, it can have a significant voltage drop and still be pssing current). Anyway, if there is a fault which causes it to switch mroe slowly, the monito can still appear to work fine, but the transsitor will run hot. And it might well fail after a few hours of continuous operation. NAsty, beacue averyything looks fine until you've got the case on and you've returned it ot the customer... Dno't feel the transistor case to see if it's getting hot. The case is the collector connection and there are high voltage spikes 9kV range) there. Not enough to do you serious damage, but cetainly enough to make you jump. -tony