On Sun, 2008-02-10 at 21:01 +0000, Barry Samuels wrote:
My dedicated MythTV computer has now been removed from its cardboard box and has been put into a proper case.
However when it's running it causes interference on medium wave on my wife's radio. Her own computer, which is nearer the same radio, does not cause any interference.
Did it do this when also in the cardboard case ? I presume so
What component could it be, in the MythTV box, which is causing this interference?
I have had this before with things like Studio PC's causing problems with audio equipment and have always managed to trace it down to one of the following.
Bad earthing, either mainboard to case or mains earth to case at high resistance.
Missing EMI shields in empty drive bays etc...usually they are punch out when drives are fitted so a secondhand case may have some holes here, missing pci slot blanks can also make a surprising difference (and also bugger up the airflow in your case)
The ATX connector backplate (where the audio and vga, serial, parallel connectors are) yes they are earthed to the case and it makes no sense..but they have little fingers on the inside that should touch metal parts of the connectors on the mainboard..make sure they do...if the mainboard is earthed down via the mountings you can be forgiven for making the assumption that this isn't relevant but earth paths don't always work quite like that so check em.
Cases like those with perspex windows in the side etc...it is pretty much impossible to get good EMI performance out of a PC built from generic components unless it is in an earthed metal tin
As Matthew suggested a peripheral component like your TV card.