[mythtv-users] Hum on analog audio to TV

[Allen Edwards]

They don't build them that way any more.  They used to put capacitors from
each side of the outlet to the chassis for RF suppression.  The problem was
that this put the chassis at 55 volts.  It really should not have caused
problems to short the grounds together even at that.  May be better to do it
with things unplugged thought so you don't have the charge in the capacitor
to short out.  That is probably what fried your traces.
I once had a similar set.  The little thing in my bathroom that puts the
drain down in the sink kind of wrapped abound the spout.  When you turned
it, you could see sparks.  It was caused by the grounding of the TV going
through the water pipes and somehow having a path through that sink spout.
 It was freaky.

Allen


On Fri, Oct 24, 2008 at 10:42 AM, Darrin <mtv at aperature.org> wrote:

>
>
> On Tue, Oct 21, 2008 at 5:16 PM, Robert Johnston <anaerin at gmail.com>wrote:
>
>>
>>
>> * Connect the grounds of the two devices together. This should eliminate
>> the Ground Loop, but may not be possible, as the TV may not have a
>> grounding screw/jack (The "Ground" on a PC is the case).
>>
>> * Finally, if none of those work, you'll need to get an isolation
>> transformer.
>>
>> For more details, see here:
>> http://en.wikipedia.org/wiki/Ground_loop_(electricity)<http://en.wikipedia.org/wiki/Ground_loop_%28electricity%29>
>> --
>> Robert Johnston
>>
>
> I'd look for an isolation transformer before I tried hooking the grounds
> from 2 separate devices together.  Some devices use a hot chassis, so
> attempting to connect them together could cause a short circuit.
>
> When I was young and stupid, I once connected the ground probe of an
> oscilloscope to a television set I was working on.  When I turned the TV on,
> I vaporized over 12 inches of copper traces on the board, blew several
> components in the power supply section, and set the fire alarm off in the
> building.  Needless to say, I never did that again without having an
> isolation transformer on hand.  It won't happen very often, but when it
> does....
>
> --Darrin
>
>
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