QDK TE555 Monitor Problem 

This monitor came in with no power symptom. Upon checking found the horizontal output transistor (HOT) completely shorted between all the legs. The part number is 2SC5296 and as mentioned before do not straight away replace the part and switch on the monitor as it might blow the HOT again. You have to find out why the HOT blow. It could blow by itself (due the transistor own life span which is very rare) or some other components that link to the transistor that is faulty which is quite common. As usual I've got to check the flyback, b+ line and some other components that link to the HOT. All of the major components that link to the HOT seems to be ok.

Close inspection at the horizontal output transformer area found the supply voltage resistor to the horizontal output transformer dry joint at one leg. Due to this intermittent supply, the output waveform of the transformer definitely affected and thus the HOT would be affected as well and this blow the HOT. Replacing the HOT and solder back the dry joint solved the problem. Conclusion- first I thought it could be a faulty component that blow the HOT and it turned out to be only a dry joint. So in future do not overlook dry joint otherwise you might end up unable to solve the problem.

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Author By : Jestine Yong