Weird audio problem with home theatre setup

[Agentbolt]

So today during a brief outage from my Cox cable, I heard an awful humming noise coming from the TV. I also noticed (due to a pure black screen) very light horizontal bars moving slowly up the TV. I have a 32 inch LCD HDTV and a Cox set top box. Normally I can't hear it because there's other sounds coming from whatever's on, but the hum is still there and I can hear it if I turn up the TV loud at all, and the rolling bars are definitely noticeable.

I googled this stuff and everything seems to point to something called a ground loop feedback, or something. Basically there's a bad ground somewhere. So I've done about 3 hours of troubleshooting and come up with the following info:

#1. The humming disappears if I unplug either the Coax cable from the set top box, or the Green component cable from either the set top box or the TV.

#2. The humming disappears if I only plug in, say, a DVD player. With either component or composite cables, as long as whatever box I'm plugging into the TV doesn't have a Coax cable running into it, there's no hum.

#3. The humming happens whether I have my digital cable set top box plugged in, or a VCR, so long as a Coax cable is running through the box.

#4. I've tried switching electrical outlets, plugging it into a surge protector, plugging it into a different Coax outlet in the wall upstairs, and none of those do anything, the humming/bars continue.

#5. If I plug the coax line directly in the TV, there's no humming.

So what the hell is it? I feel like I've elimated everything it possibly could be. It's not the cables, because they work fine if plugged into my DVD player. It's not the electrical because there's no humming if I'm using a DVD player or like, my N64. It's not the Coax cable because it works fine when plugged directly into the damn TV. It's not the set top box because the same thing is happening with a VCR.

Someone help me, please!

 

[The Boston Dangler]

is the cable grounded as it hits the house?

 

[Agentbolt]

I have no idea. I am not 100% sure how to even check that.

 

[Modelworks]

Go outside where the cable connects to the house and there should be a thick wire connected to the splitter that runs back to your houses electric meter.
check and make sure the connections are tight, not corroded, etc.

 

[Agentbolt]

I've searched everywhere and cannot find where the cable goes into this place. I live in a townhouse, so there's 3 houses connected to mine, all with fenced in back yards, so I can't check the perimeter in the back, but I couldn't find the damn wire ANYWHERE. From the coax outlet in my wall it goes through the wall to an outside closet, and then goes through the ceiling of my closet into the wall of the building and goes into the upstairs bedroom, but it doesn't come out of the wall up there so it must continue to wherever it's going inside the wall.

Is there anything else I can do to test the cable line coming in? Is there a filter or something I can screw it onto to attempt to fix this problem? In my head I'd already ruled out the coax line because there's no hum or picture distortion when the coax line is plugged directly into the TV, only when it's going into a set top box or VCR first.

 

[Modelworks]

There are ground loop isolators for cabletv but they will disrupt any digital signals on the line. So if you got digital channels you could lose them with the isolator.

I would contact the cable company and have them fix it.

If they are not willing there is another fix, although I don't really recommend it as its not the best way to solve the problem.

get a grounding block like the one pictured here.

http://www.partsexpress.com/pe...D=7&Partnumber=090-338

get a short peice of small gauge wire, about 20awg or so.
Attach the block to the cable line, then attach the wire to the screw on the block and attach the other end of the wire to the screw on the faceplate of an electrical outlet.
That will ground the cable line.

The preferred way though is to get the cable company to fix the ground connection.

 

[The Boston Dangler]

call the cable company and tell them you are getting 60 Hz hum from the cable.

 

[spidey07]

Originally posted by: The Boston Dangler
call the cable company and tell them you are getting 60 Hz hum from the cable.

Agreed. You've got groundloop hum and since you've isolated it to the cable service...call them. This is a safety issue as well.

Somebody else could have been messing around with the wires outside your townhouse (cable service was out and another joe-blow was messing with the entrance. Specifically tell the cable company they need to check the ground as the service enters your townhouse.

 

[Agentbolt]

I will do that. In the meantime I've hooked up a Phillips surge protector with coax inputs and that's taken care of the issue for now.