NotTaR of Television Sets : Horizontal output transistors blowing at..  
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Horizontal output transistors blowing at random intervals

The HOT may last a few months or years but then blow again.

These are among the hardest problems to locate. It could even be some peculiar combination of user cockpit error - customer abuse - that you will never identify. Yes, this should not happen with a properly designed TV though newer horizontal processor chips are quite smart about preventing HOT killing signals from reaching the horizontal driver.

However, a combination of channel changing, loss of sync when switching video sources, and frequent power cycles, could test the TV in ways never dreamed of by the designers. It may take only one scan line that is too long to blow the HOT.

On the other hand, the cause may be along the lines of those listed in the section: Horizontal output transistors keep blowing (or excessively hot) and just not as obvious - blowing in a few days or weeks instead of a few seconds but in this case, the HOT will likely be running very hot even after only a few minutes.

Another possible cause for random failures of the HOT are bad solder connections in the vicinity of the flyback and HOT (very common due to the large hot high power components) as well as the horizontal driver and even possibly the sync and horizontal oscillator circuits, power supply, or elsewhere.