This is a problem which is not going to be easy to identify. One possibility
is a drive problem. The messed up sync resulting from swtiching channels,
or changing input connections might be resulting in an excessively long scan
time for just one scan line. However, this may be enough to cause a current
spike in the horizontal output circuit or an excessive voltage spike on the
collector of the horizontal output transistor. Normally, the HOT current
ramps up during scan. During flyback, the current is turned off. This
current is normally limited and the voltage spike on the collector of the
HOT is also limited by the snubber capacitors to a safe value. If scan time
is too long, current continues to increase. At some point, the flyback core
saturates and current goes way up. In addition, the voltage spike will be
much higher - perhaps destructively so.
|NotTaR of Television Sets : Fuse blows or TV blows up when sync is d..
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Troubleshooting these sorts of problems is going to be tough. However,
a likely area to investigate would be:
Drive circuitry for the HOT including the coupling components.
The chip that generates takes the sync input and generates the horizontal
A bad low voltage regulator might permit the B+ to rise to excessive levels
during black scenes (i.e., video mute during channel changing).