"Rutro" wrote in message
lkaboutelectronicequipment
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Seems to be from the HV circuit. I was considering changing the flyback.
Any thoughts?

Not familiar with the model but sounds like it could a be crt flashover.
Measure cathode and grid voltages of the crt when the fault is not present
and then see what changes when the fault occurs. Finding out whether it is
an increase in grid volts, or a decrease in cathode volts, should narrow
things down a bit - if it's not the crt.