AVS Forum banner
1 - 7 of 7 Posts

·
Registered
Joined
·
16 Posts
Discussion Starter · #1 ·
A while back, I had a ground loop problem--and solved it by putting an isolating transformer on my incoming cable line.


Recently, my old 30" Sony HDTV (CRT) died and I replaced it with a 40" XBR2 LCD TV.


Suddenly, my ground loop problem was back with a vengence.


Background: I have a bunch of A/V equipment, including my TV, connected to a surge protector in one room. I have my PC in another room and another TV in my bedroom.


I have run a composite video plus the L&R audio channels through a Radio Shack distribution amp. from the cable box to both my PC and my bedroom TV.


I don't seem to notice much problem on the bedroom TV (an old Sony non-HD CRT TV in a cabinet; yeah, it's old--but it works and was free!). However, the PC has a really nasty hum and the video picture has a scrolling band.


I discovered that unplugging the new Sony LCD TV makes the problem go away. I then discovered that ungrounding that TV also made the problem go away.


I suppose I could leave it ungrounded, but that's probably not the best solution.


Since most equipment isn't actually grounded (or is grounded through the neutral side of the power plug, since it doesn't have a third ground pin)--there aren't a lot of places for ground problems to come into play. My PC is grounded as is my TV--but that's about it.


With my TV & PC quite some distance apart, what can I do to fix a problem like that? I seem to have about 0.1 VAC trying to from the TV's ground plug to the outlet and about 1mA current flowing (according to my digital multimeter).


I don't have thousands of dollars to spend (one site sells "isolating" devices for $500-$900 or so--that's way out of my price range).


Thanks,


...Rob
 

·
Registered
Joined
·
16 Posts
Discussion Starter · #2 ·
Quick followup:


Originally, the outlet for the main TV & other equipment was powered from one side of the breaker box while the outlet for the PC was powered from the other (i.e., the "hot" sides were on opposite legs, with 240 VAC between them). Switching the breakers to put them on the same side made no difference at all.


Also, their grounds and neutral wires are connected on opposite sides of the box (the box has two columns of breakers & corresponding grounding posts).


The ground wires are tied into the grounding post towards the top while the neutral wires (white) are tied in towards the bottom of each of the columns. Yes, all of the ground wires AND all of the neutral wires are essentially connected together and all are tied to the "earth ground" that runs outside.


I measured a 1/100th VAC difference between the two neutral wires but no difference between the grounds.


Running a long extension cord through the house so the PC was connected to the same outlet as the TV seemed to help. Is my only option to drop another outlet for my PC off the same circuit as my TV?
 

·
Registered
Joined
·
1,856 Posts
Have you double checked your cable ground problem? It could also be that you have two "grounded" components running with a number of Neutral to Ground components. So esentially you're creating two distinct paths to ground, which gives you a ground loop. Instead of an isolator, can you ground your cable to the house ground? If so, and if that doesn't help, then you should probably run the PC and the TV through the same outlet or at least provide the same path to ground for both components.
 

·
Registered
Joined
·
16 Posts
Discussion Starter · #4 ·
Thanks.


Before I put the isolator on the cable line, I tried those sorts of things. The only thing that really helped was isolating the cable. I haven't re-done those experiments this time.


Also of interest: I don't seem to have a problem with the cable at the moment. All the TVs AND my PC are connected to the cable (the PC has a tuner card) and I don't seem to be getting any ground loop problems through that. It's only when I connect the video or audio into my PC's sound card that I notice the ground loop problems (and, then, ungrounding either the PC or the TV makes them go away).


What seems a bit nuts is that all the neutrals and grounds are tied together in the breaker box--so I know they all have a common ground. And, my house isn't that large so the wire lengths aren't that much different.


I wonder if it will hurt to have the TV running without a ground for a while--until I can try putting the PC on the same circuit?
 

·
Registered
Joined
·
66 Posts
I track down and fix video distribution problems for a living and I have found that some TV's, especially newer sonys have problems with feeding back Ground loop Noise through the Component and composite connections as they are all grounded together. Here's a test to do: turn the TV on the input where you're seeing the ground loop noise/hum and disconnect the Coaxial cable from the antenna connector. If it goes away, that's your culprit and that antenna cable will need to be better grounded.


let us know what happens
 

·
Registered
Joined
·
16 Posts
Discussion Starter · #6 ·
I'm seeing/hearing the problem on my PC (not my Sony TV).


But, it apprears that the problem is coming from the ground pin on my Sony TV (or on my PC), because disconnecting the TV (or the PC) from the ground solves the problem.


The cable is isolated and removing it didn't solve the problem.


Thanks.
 

·
Registered
Joined
·
16 Posts
Discussion Starter · #7 ·
A roll of 12-2 romex wire, a new circuit breaker, and an outlet box later....voila, my problem is solved.


I rewired the TV's outlet onto a brand new circuit straight from my circuit breaker box, then went across the house to the room my PC was in and installed a new outlet on that same circuit. Now, things work nicely and QUIETLY!


No need talking about the other circuit I added and the rewiring I "just had to do" (well, while I was doing some wiring, I might as well do some more :) ).


Major home-buying tip: ranch houses with unfinished basements rock! They sure make projects like this a WHOLE lot easier!


Thanks for the ideas.


PS: I wonder if the current from the groundloop problem was either 1) frying my PC's motherboard or 2) causing erratic behavior. I was having some bizarre problems with one of my IDE drive changes about the time all this was going on. I took the drive on that IDE chain out & just used my main drives. I haven't had the guts to put it back into place, but I do kinda wonder if the ground loop problem was responsible for my PC's strange behavior. It certainly isn't likely to have helped anything!!
 
1 - 7 of 7 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top