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RE: That's the, aptly named, death cap. Nt

Posted by JURB (A) on October 29, 2016 at 11:21:45

In Reply to: That's the, aptly named, death cap. Nt posted by viridian on October 28, 2016 at 20:46:17:

That cap should not be of a high enough value to deliver a lethal electric shock. It is there to reduce AC noise between the chassis and ground, and you'll find many of them to be a capristor, meaning it has about a 2.2 meg ohm resistor in parallel with it to discharge static electricity.

Music equipment is different. Remember the movie "Far Out Man" with Tommy Chang after Cheech and him split up ? "That roadie tried to kill me with his guitar". I also remember bands playing outdoors on top of sheets of plywood to insulate them from earth ground. They had to hard ground the equipment because it was in an electrically noisy environment. You could have 100s of florescent lights, and look up limelight, maybe even arc lamps. That's why they use XLR (totally balanced) cables for microphones.

If you are getting a shock, that capristor or something else is shorted. Regular home audio equipment is not hard grounded like pro stuff was. But there has to be something to keep it from picking up a 100,000 volt static charge in the dead of winter when the humidity is almost in the negative numbers.

You can do what's called a static (not electricity but I mean not live) line leakage check with an ohmmeter. With the unit unplugged and the power switch on, put one probe on BOTH prongs of the power plug and then check every exposed metal part on the unit, this includes the grounds on the RCA jacks on the back of course. It should measure over one meg ohm. It should measure something though unless your highest scale is only like 10 meg ohms. If it measures less than one meg ohm there is probably a problem, and on older equipment it could be corrosion somewhere, possibly even inside the power transformer. A problem like that should be addressed because it is likely to conduct more with a higher voltage applied than your ohmmeter. Then a live line leakage check should be performed and that is probably beyond the skill set of the hobbyist. Actually there is an easier way if you happen to have a spare GFCI outlet laying around. But we'll burn that bridge when we come to it.

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