I have a dead colour TV that I'm finally having a go at fixing - no expert on these things though.
The chopper transistor on the switch mode supply has shorted out. Replaced it and same again (very quickly fails), so there is a problem somewhere. I have a couple of questions:
- Anyone know a good online description, in detail, of the operation of these supplies. For example, the feedback from the output side of the supply that apparently controls the chopper transistor is through a single four pin IC that I can't identify. I suspect it may be an optoisolator but not certain. It carries markings OA . P621 . 4 G., The manufacturer logo looks like a "T", but don't recognise it (its not an SGS Thomson logo).
- I can think of at least two possible generic causes of the failure: a) Failure somewhere in the actual TV circuit that is causing excessive current drain and overloading the power supply, eg horizontal output transistor (but this looks OK). b) Failure in the switchmode supply itself such that the chopper transistor is forced permanently on, or is being driven at a much higher duty cycle than it can handle. Are there any other possibilities, and testing strategies?