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

Hummmmmmmmmm (feed back loop ) ....
 

"b393capt" wrote in
oups.com:

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.



Bad house battery cell.....The charger is pulsating its high resistance,
causing a pulse at the AC line frequency on the DC power supply of
everything aboard....sorry.

It could also be corroded contacts between the charger and the battery
post. I hope it is for you.

Chargers don't put out DC. They put out pulses of DC at the AC line
freq. Superchargers with computers put out pulses with measuring times
in between pulses to see how they are doing. That'll really drive
everything crazy if there's a resistance from corrosion or a bad battery
cell with low specific gravity caused by cell sulphation. Cell
resistance from the low gravity is effectively in series with the cell's
"battery". So, when you shove a 10A pulse through a bad cell, the
resistance in series drops some of the drive voltage, causing it to add
to the cell voltage during the pulse. If the gravity is really low, the
pulse can go over 20 volts on some chargers.

The series resistance is also easy to spot in DC cabin lighting, either
type. When you turn on another load, without the charger on, the lights
dim that are already on. When the bilge pump cycles, the lights dim, for
instance.

Finding which one of these problems is quite easy. Bypass the
connections the house has by putting a DC voltmeter (prefer a DVM)
directly across the battery posts (not the clamps on the battery posts).
Load the battery down without the charger running by turning on your big
loads while monitoring the meter. Good batteries hardly drop at all, a
few tenths of a volt. Batteries with poor cells drop more because the
series resistance inside the cells drops the voltage when you pull heavy
current through it.

Are all the cells full of DISTILLED water? I regularly am asked to
troubleshoot problems like this. Way too many times I open the caps on
the batteries, especially batteries some idiot or idiot boat company has
made really hard to get to, and find the batteries way low on electrolyte
because noone ever topped them off. The guy at the boat shop said they
were "maintenance free", to get them to buy them. Bull****. No such
battery exists. Some just make it difficult or impossible to top off the
lost electrolyte, like gelcells and AGM overpriced crap.

If you must add water, and the water is below the plate tops, give the
batteries a week to recover from the abuse before trying the testing
again. Sometimes they do...sometimes it's gone too long and they are
sulphated, the bottom of the plates eaten away.

Many "hum problems" are cured with DISTILLED water....(c;

Hummmmmmmmmm (feed back loop ) ....
 

Thankyou !!

This did the trick, no more humming !!

Dan

Hummmmmmmmmm (feed back loop ) ....
 

Tapio,

A galvanic isolator in the audio RCA cables might fix it.

Thankyou !! This did the trick, no more humming !!

Dan

Hummmmmmmmmm (feed back loop ) ....
 

"b393capt" wrote in
ups.com:

A galvanic isolator in the audio RCA cables might fix it.


Hmm...you should try finding it in a big stadium with 100 mic jacks, 24
speakers in the vaulted ceiling all hooked to 12 different AC circuits.

Ground loops drive PA system technicians crazy.....