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
|NotTaR of Television Sets : Arcing, sparking, or corona from CRT HV ..
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There are two likely causes:
- 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.
- 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".