NotTaR of Television Sets : Arcing, sparking, or corona from CRT HV ..  
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Arcing, sparking, or corona from CRT HV anode (red wire/suction cup)

Symptoms could include a sizzling corona or more likely, an occasional or rapid series of sharp snaps - possibly quite loud and quite visible - from the anode connection (at the suction cup) on the CRT to the grounded coating on the outside of the CRT or a chassis ground point (or any other conductor nearby). Corona is a high resistance leakage through the air without total breakdown. The snapping is caused by the sudden and nearly complete discharge of the CRT anode capacitance through a low resistance ionized path similar to lightning.

There are two likely causes:

  1. Dirt, dust, grime, around and under the suction cup on the CRT are providing a discharge path. This may be more severe in humid weather. Safely discharge the HV and then remove and thoroughly clean the HV suction cup and the area under it and on the CRT for several inches around the HV connection. Make sure there are no loose wires or other possible places for the HV to discharge to in the vicinity.

  2. The high voltage has gone through the roof. Usually, the X-ray protection circuitry should kick in but it can fail. If cleaning does not help, this is a likely possibility. See the sections: "High voltage shutdown due to X-ray protection circuits" and "Excessive high voltage".