[mythtv-users] Humming Noise coming from LCD tv

Stephen P. Villano stephen.p.villano at gmail.com
Tue Apr 1 07:25:43 UTC 2014


On 4/1/14, 3:19 AM, Simon Hobson wrote:
> Philip Isaacs <showcasefloyd at gmail.com> wrote:
>
>> Okay, so this is slightly off subject, but I've hooked up my Myth PC to my LCD TV via a DVI to HDMI adapter. I then ran a single audio cable from the sound card on the PC into the audio port in the back of the TV.  The picture looks great but there's a annoying hum coming from the TV now. It's pretty loud too. I tried switching out the cables but I'm having no luck. Any suggestions on how to fix this?
> As Will says, first thing is make sure they are both on the same socket - not separate sockets on the same faceplate* but the same socket (ie use an extension or adapter). If the TV has a 2 pin plug, try reversing it in the socket though I don't think that will help.
>
> After that, if you can find an accessible screw on the TV chassis (and assuming it's a 2 pin plug), connect a short piece of thick wire between that and the PC case. Might be worth checking that the PC is in fact properly earthed while you are at it !
>
> With many modern TVs, there is no earth to the chassis (and electronics common (ground)). There is some filtering on the mains input, and the end result of various factors usually means that there is a very weak connection between the midpoint of the mains (so about 50-60V on the US 120V system) to the chassis. Without anything connected, the chassis will literally be at an AC voltage of several tens of volts.
> Once plugged into something earthed, the chassis is earthed through that other equipment - and the signal cable. Adding a thick earth connection may avoid this aspect.
>
> If that makes no difference, try a different sound system - try plugging the PC into some powered speakers, your HiFi, or whatever and see if it still hums. It could be that the PC itself is "noisy" on the output.
>
>
> * You don't mention where you are, but I know that in the US, one wiring method involves two sockets on one plate being on separate split phases.
> _______________________________________________
>
(*My first thought*) was, *what* kind of hum is it?
Is it mains hum? For that, both advices are good.
For *other* hum, not so much so.
Hum is a relative term for non-technical people. It may well be mains
hum, it may well also be 1kh hum or other frequency.
Back when I repaired televisions, I even heard a complaint about 10khz hum!
That last was repaired by a filter, as interference caused it due to
proximity to several high power television stations. The trick was
learning what the frequency was and knowing what the other frequencies
were and her IF frequency.

In this, it's likely mains hum, but it's always good science to be sure.  :)


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