[mythtv-users] Hum on analog audio to TV

Tom Lichti tom at redpepperracing.com
Wed Oct 22 17:43:10 UTC 2008


James Crow wrote:
> On Wed, 2008-10-22 at 08:48 -0400, James Crow wrote:
>   
>> Several great ideas so far. Let me fill in a few details. 
>>
>> 1) TV does not have digital audio input and this is in the bedroom, so
>> no receiver, etc. TV has built in DVD player and has S/PDIF _out_ , but
>> not in.
>>
>> 2) The is a slave FE. No BE, no tuners, no coax connection. Master BE/FE
>> does not have some problem so it is not on the recordings.
>>
>> 3) TV and Myth box connected to same outlet. I rewired most of the house
>> to add ground connections and I know this outlet is properly grounded.
>>
>> 4) Coax is grounded to same grounding stake as house power at point of
>> entrance to house.
>>
>> 5) Coax is connected to TV only.
>>
>> 6) I think TV has only two prong power plug not grounded plug.
>>
>> Things I will try tonight.
>>
>> 1) Flip TV power plug over to swap hot neutral.
>>
>> 2) Disconnect coax from TV. Maybe it still has ground from there.
>>
>> 3) Connect wire from PC chassis to coax outer braid.
>>
>> 4) Build isolation transformer.
>>
>> Thanks for all the ideas I will let everyone know what fixes it.
>>
>> Thanks,
>> James
>>
>>     
> During lunch I tried a few of the suggestions from the list. Here is the
> outcome:
>
> 1) Flip TV power plug over to swap hot and neutral.
> -Not possible because it is a polarized plug. I would have to wire an
> adapter to try this.
>
> 2) Disconnect coax from TV.
> - This fixed the buzzing with the downside of losing live tv through the
> tv set.
>
> 3) Connect a wire from PC chassis to coax outer braid.
> - This decreased the volume of the hum, but it was still present.
> Perhaps a soldered connection instead of my fingers holding it would
> produce better results. Would connecting the coax braid to house ground
> accomplish the same thing as chassis ground to coax? I have an unused
> ground plug in the outlet I could wire to the coax braid.
>
> Any thoughts on this, or am I pretty much at building an isolation
>   
These were my EXACT symptoms, and it was solved by grounding the cable 
coming into the house. I know you said it was, you might want to just 
verify that.

Tom



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