[R-390] thanks

[Shoppa, Tim]

Don writes:
> Tim wrote:
>> Line filter caps have this tendency to begin failing on line voltage 
>> peaks. So what you get is a 60Hz or 120Hz noise coming from the 
>> capacitor as the layers begin to arc over. If it's not in a metal 
>> can, it is very very common to see wax or fumes coming from a wax 
>> capacitor at this point, and sometimes you can see little sparks 
>> inside if the arc-over is happening near the surface. It is also 
>> actually audible, either hearing a 60Hz/120Hz buzz or a curdling 
>> noise as wax melts or vaporizes. In a metal box there's much less to 
>> see but I can believe that a 60 Hz or 120Hz buzz could be heard.

> This is a plausible source of mechanical buzzing, but in this case it 
> may be inconsistent with the reported finding of 60 volts on the 
> ungrounded chassis.  Unless all four capacitors were failing in 
> exactly the same manner at exactly the same rate (which is highly 
> unlikely), one would expect that the voltage divider formed by the 
> caps would become unbalanced and there would be a different, and 
> likely varying, voltage on the ungrounded chassis.

I don't think we're talking about the same thing. A perfectly good, 100% new, line filter will put 60VAC on the chassis if you lift the ground. You don't need any failure of any component or subcomponent at all.

Tim.


































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