[sdiy] EMC mains filter failure - why?

[Oakley Sound]

 > Now can anyone tell me the point of this filter?

Its a RFI filter. That is, it gets rid of high frequency noise on the 
supplies that could affect or infect the audio circuitry. HF noise on 
mains lines comes from a variety of sources; SMPS and electro-mechanical 
devices being just two examples.

Its also prevents noise going the other way too. In a linear supply, 
this would rectifier switching spikes mostly.

 > Im told that this was probably caused by a problematic connection 
external to the device?

Yes this is possible. A poor connection made inside the IEC socket part 
of the filter would create localised heating and failure of the part. I 
have seen solder connections melt on the reverse side of an IEC inlet 
due to a faulty IEC plug. So it can get very hot.

Tony

www.oakleysound.com