Hummmmmmmmmm (feed back loop ) ....
 

I am getting a humming sound in my boat TV, new installation, maybe
someone has solved this before.

I have a standard Sony 19" LCD TV, and a automobile 12 VDC DVD player.
They are connected to each other via a cable with 3 RCA jacks (left,
right, video)

When I plug the TV into shore power, everything works perfect. Great
sound & picture.

When I plug the TV into 12 VDC (via an 12vdc to 18vdc step up
transformer), I get a light humming sound in the TV, picture is still
great.

As I go to debug this I notice:
1) Moving wires, has no effect on hum. (neither louder or softer)
2) If I power off DVD player only, hum remains.
3) If I unplug DVD player (from 12vdc), hum disappears. (even with RCA
connected)
4) If I unplug the RCA cables, hum dissappears

So clearly the DVD is the source of the hum (not the 12-18vdc step up
transformer), or is it ?

Any thoughts ?
Dan

Hummmmmmmmmm (feed back loop ) ....
 

whenever i have any kind of a problem like this i always try three
things first, in order ..

1) wrap the signal and power cables multiple turns around a ferrite
rod, then ...
2) if problem persists, try another (better) ground, then ...
3) if problem persists, re-route signal cables so they aren't following
beside other wires, especially a/c power wires or wires from electric
motors ...

then once i've satisfied those superstitions i try to actually figure
out what is going wrong, what the real trouble is .. lol

if i had to guess i'd say it's the inverter ...

b393capt wrote:
I am getting a humming sound in my boat TV, new installation, maybe
someone has solved this before.
[snip]

Hummmmmmmmmm (feed back loop ) ....
 

No Inverter is in use. The TV (thru a 12V to 18V converter) and the
DVD (natively) are connected to 12VDC. At the time, the boat was also
disconnected from shorepower.

Hummmmmmmmmm (feed back loop ) ....
 

Shut your battery charger off, see if it goes away.

Hummmmmmmmmm (feed back loop ) ....
 

"Capt John" wrote in message
ups.com...
Shut your battery charger off, see if it goes away.

Or the 12-18V converter, which also contains an HF switcher.

Meindert

Hummmmmmmmmm (feed back loop ) ....
 

The battery charger was not on (I was also disconnected from shore
power)

In one of my tests I did remove the 12V-18V converter which powers the
TV. When I plug the TV into shore power, everything works perfect.
Great
sound & picture.

Hummmmmmmmmm (feed back loop ) ....
 

Help ... don't forget me

Hummmmmmmmmm (feed back loop ) ....
 

Help ... don't forget me

Hummmmmmmmmm (feed back loop ) ....
 

b393capt wrote:
As I go to debug this I notice:
1) Moving wires, has no effect on hum. (neither louder or softer)
2) If I power off DVD player only, hum remains.
3) If I unplug DVD player (from 12vdc), hum disappears. (even with RCA
connected)
4) If I unplug the RCA cables, hum dissappears

Sounds like a ground loop on the 12 VDC side to me. A galvanic isolator
in the audio RCA cables might fix it. This leaves the video signal
unisolated, but it might be enough for getting rid of the audio hum.
Note that this device is not the same thing you can put on your shore
power line, to prevent electrolysis on your boat's underwater metal parts.

This picture shows what the device I'm talking about might look like:
http://www.biltema.fi/osteri/data/Kuvat/31_441iso.jpg . There are small
audio transformers inside the box, they break the galvanic connection
between the DVD player and TV, but let audio frequencies pass. It should
not cost much more than 20 dollars/euros. You might find one in an
electronic parts store or in a shop that specializes in audio equipment.

Tapio

Hummmmmmmmmm (feed back loop ) ....
 

In article , Tapio Sokura wrote:
b393capt wrote:
As I go to debug this I notice:
1) Moving wires, has no effect on hum. (neither louder or softer)
2) If I power off DVD player only, hum remains.
3) If I unplug DVD player (from 12vdc), hum disappears. (even with RCA
connected)
4) If I unplug the RCA cables, hum dissappears

Sounds like a ground loop on the 12 VDC side to me. A galvanic isolator
in the audio RCA cables might fix it. This leaves the video signal
unisolated, but it might be enough for getting rid of the audio hum.
Note that this device is not the same thing you can put on your shore
power line, to prevent electrolysis on your boat's underwater metal parts.

This picture shows what the device I'm talking about might look like:
http://www.biltema.fi/osteri/data/Kuvat/31_441iso.jpg . There are small
audio transformers inside the box, they break the galvanic connection
between the DVD player and TV, but let audio frequencies pass. It should
not cost much more than 20 dollars/euros. You might find one in an
electronic parts store or in a shop that specializes in audio equipment.

Tapio

A HREF="http://www.radioshack.com/product/index.
jsp?productId=2062214&cp=&origkw=loop+isolator&kw= loop+isolator&parentPage=search"isolator/A