Problems with Ground Loops and Vido HUM Bars
Doug Shuffield
I am having a problem isolating where my ground loop problem is coming
from. The symptoms I see are Bars on my TV which scroll up the screen.
The problem is these bars come and go, and when they are present they
vary in intensity. I have verified that the cable ground is connected
to the earth ground on the outside of the house, but the problem still
remains. This problem is also screwing up any attempts to do video
electronics experimentation. I am really tired of seeing these bars and
any help you could give would be appreciated.
IF you could respond via email to dshuf...@symtx.com and here to the
group to help out any others with this same problem.
All Hummed out...
- Doug
Mark Kinsler
Doug Shuffield <shuf...@symtx.com> wrote:
>I am having a problem isolating where my ground loop problem is coming
>from. The symptoms I see are Bars on my TV which scroll up the screen.
>The problem is these bars come and go, and when they are present they
>vary in intensity.
I'll bet you've got severe rf interference coming from somewhere.
Investigate with an AM transistor radio tuned to a blank spot down towards
the low end of the band. First, just listen. Does it sound, for example,
like an electric shaver? It might be. Then, take your radio for a stroll
through the neighborhood and see if you can find the offender. Might be
the thermostat on an aquarium heater (a rich source of rfi--these could
wipe out communications satellites) or it might be an intermittent arc
atop an electric pole. If you suspect a particular pole, give the suspect
pole a swift couple of kicks and see if the nature of the sound changes.
Then call the power company with your story and the pole number and
location.
If the interference seems to be coming from a neighbor's house, you'll
need to use a lot of diplomacy and hope that the rf isn't coming from the
thermostat of the heaters that he's using to dry his crop of marijuana.
I am not making this up.
A fellow named Jack Darr, who might be the best electronics writer who
ever lived, wrote a swell book about rf interference. See if you can find
a copy--I don't have a title or publisher, I'm afraid.
Mark Kinsler
--
.............................................................................
Interpretation and instruction in physical science and technology.
Athens, Ohio, USA. http://www.frognet.net/~kinsler
Paul Grohe
On Sat, 28 Feb 1998 20:44:17 -0600,
in the newsgroup sci.electronics.basics,
Doug Shuffield <shuf...@symtx.com>
from PSINet thoughtfully posted:
> I am having a problem isolating where my ground loop problem is coming
> from. The symptoms I see are Bars on my TV which scroll up the screen.
> The problem is these bars come and go, and when they are present they
> vary in intensity. I have verified that the cable ground is connected
> to the earth ground on the outside of the house, but the problem still
> remains. This problem is also screwing up any attempts to do video
> electronics experimentation. I am really tired of seeing these bars and
> any help you could give would be appreciated.
1. Do these bars show up on other TV's connected to the same
cable?
2. Is your TV connected to anything else? A/V receiver? VCR?
If so, unplug *all* the equipment and plug it in one-at-a-time
until the hum appears. If you have an AV receiver in the system,
try running a jumper wire from the incoming CATV ground at the TV
to the receivers chassis ground (usually the "phono ground
screw").
If you have any devices with un-polarized plugs, unplug them and
rotate them 180 degrees, and plug them back in.
3. If you connect a temporary antenna and view "off-the-air"
signals, are the bars still there?
If you still cannot eliminate the hum, try building a simple
"ground isolator" out of two 75-300 ohm baluns, as described in
the below link:
http://www.hut.fi/Misc/Electronics/docs/groundloop/antenna_isolator_building.html
Place it as close to the TV as possible.
Good Luck!
Cheers,
Paul Grohe
---------------------------------------------------------------
Paul Grohe National Semiconductor Corp.
Sr. Electronics Technician Santa Clara, CA. USA
http://www.national.com
NORTH AMERICA EUROPE
1 (800) 272-9959 +49 (0) 180-532 78 32
mailto:sup...@nsc.com mailto:europe....@nsc.com
Usenet Disclaimer: Any opinions expressed are mine, not NSC's
---------------------------------------------------------------
Steve
I have an idea. Disconnect anything that you have hooked up, house amps,
wire, splitters, etc. Then if you still have the problem call the cable
company up and have them come out and fix it for free! If the problem goes
away when you disconnect everything then you know the problem is in your
stuff!
Jerry G.
I would check out the main powersupply for any failing electrolytic filter
capacitors...
I would also try the TV in another AC outlit, or a similar one in the same
AC outlit to make sure you don't have a ground fault in the AC outlit
feeding the power to the TV.
--
You must remove the NOSPAM from my internal
address to reply to me. Sorry about that...
Reply To: jerryg...@total.net
If It Works, Don't Fix It !
If It Don't Move, Slap It !
If It Don't Make Noise, Shake It !
If It's Broke, Then Fix It ... !
If You Don't Know How To Fix It, Give It Out !
W-Site http://www.total.net/~jerryg
-----------------------------------------------------------------------
Doug Shuffield wrote in message <34F8CB...@symtx.com>...
|I am having a problem isolating where my ground loop problem is coming
|from. The symptoms I see are Bars on my TV which scroll up the screen.
|The problem is these bars come and go, and when they are present they
|vary in intensity. I have verified that the cable ground is connected
|to the earth ground on the outside of the house, but the problem still
|remains. This problem is also screwing up any attempts to do video
|electronics experimentation. I am really tired of seeing these bars and
|any help you could give would be appreciated.
|
Jon Garver
In article <34F8CB...@symtx.com>, shuf...@symtx.com wrote:
>I am having a problem isolating where my ground loop problem is coming
>from. The symptoms I see are Bars on my TV which scroll up the screen.
>The problem is these bars come and go, and when they are present they
>vary in intensity. I have verified that the cable ground is connected
>to the earth ground on the outside of the house, but the problem still
>remains. This problem is also screwing up any attempts to do video
>electronics experimentation. I am really tired of seeing these bars and
>any help you could give would be appreciated.
>
>IF you could respond via email to dshuf...@symtx.com and here to the
>group to help out any others with this same problem.
>
>All Hummed out...
>- Doug
lightning. At the time I didn't make the connection and thought it was in a
bad cable ground. After going thru the splitters checking connections etc., I
come to the conclusion that something in the shop was radiating a spurious
signal. Well to make a long story short, it was my bench circuit surge
protector. It has a relay in it that developed bad contacts after the
lightning strike. This probably isn't your problem but I thought that I would
share this little tid bit. - Jon
Jon Garver
Heritage Television Service
Monticello,IN
Michael Caplan
Some sets have an isolation box between the tuner and the rear panel
cable F connector. The box isolates the tuner (i.e. chassis) ground
from the cable ground (which you confirmed) at low frequencies.
There are two modular networks inside. Each is a pFd range capacitor
in parallel with a megohms + resistor. One is connected from the
tuner coax cable shield to the isolation box case, the other is in
series with the center conductor. If the cap shorts, especially in
the network between the tuner coax cable ground and the isolation box
case, a 60 Hz ground current is established when the cable is
connected and the video symptom is exactly as you indicated.
(I have also seen instances where the F connector, which is probably a
press fit into the isolation box case, comes loose and is twisted when
a cable is connected (or disconnected). This can wreck the wiring
inside as well as affect the signal. If it is just a loose connector
the symptom usually is a noisy signal.)
You didn't indicate what type of set you had so it's difficult to be
more specific. The example I am using is from a Samsung CT 5071XVC,
(that also had a polarized plug) but I have seen several makes with
these isolation boxes.
Michael Caplan CET
-------------------------------
On Sat, 28 Feb 1998 20:44:17 -0600, Doug Shuffield