Re: CRT static charge

Ed Breya

I second Eric's suggestion, especially regarding the "back of the hand" test, which makes a great static charge detector. With a small CRT like in a scope, you can just place your knuckles against the CRT face.

If the CRT lights up and seems to operate normally, then eventually the sound should go away as the static charges in the materials equalize. The root cause may be that you did too good of a job cleaning the face parts. I have often said that dirt and grime can be your friend, when it comes to static electricity problems. After a CRT has been in service for a while, ambient moisture and particles form a natural static discharge path on the surfaces. If you've used an anti-static wipe on the plastic shield, that should have similar effect. Maybe try the same on the CRT glass face too, and be sure both sides of the plastic shield are treated.

Of course, this all assumes the sound really is just discharge at the face. If it's something else inside, then it's a different story. Try looking at the scope, opened up, in the dark. Sometimes you can see discharges around the HV parts. Also, if there's enough, you can smell ozone and nitrogen oxides in the vicinity.


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