AVS › AVS Forum › Display Devices › Display Calibration › Ground Loop Question / Assistance
New Posts  All Forums:Forum Nav:

Ground Loop Question / Assistance

post #1 of 21
4/23/07 at 12:04pm
Thread Starter 
I have a question about ground loop interference on displays (that I haven't seen answered).

Should I see the horizontal line moving upward all the time?

I recently rearranged my setup and now I have the horizontal line moving upward --- but I can only see it when the image is dark. When the image is bright (or even gray), one cannot see any sign of a problem.

I'm going to try the usual things: use a single outlet, check sat/cableTV, etc. But I wanted to know whether the symptom I have matches a ground loop issue.

... Altan
Reply
Reply

AVS Top Picks

post #2 of 21
4/23/07 at 12:20pm
Yes it does. One of the most common causes is cable/sat being grounded to a stand-alone ground rod, i.e. a ground rod that is not bounded to the main electrical ground. This will cause a ground loop.

Best,
jeff
Reply
Reply
post #3 of 21
4/24/07 at 11:42am
I just answered another topic similar to this one. My problem was with cheap dimmer switches near my system. They DID NOT share the same outlet or even the same fuse in the box but they still made the lines crawl up the screen!

If you have dimmers start here!!! Turn them off to see what happens! Worked for me!
Of course YMMV.

Charlie~
Reply
Reply
post #4 of 21
4/24/07 at 6:04pm
Ok, I was looking for some help here in the website on a ground loop problem around august of last year. I had these 2 barely noticeable lines moving up my screen.
Anyway....after a while i realized they were gone....I had not seen them for a long time....until now.....
The only difference is that this time they are really noticeable thick purple lines moving up my screen. Now, I dont see them all the time but once in a while they appear and today I saw them at their biggest. I got so pissed I decided to come to this site and get some help again.

I know it has something to do with an electrical problem or something because, for exaple, I have a heater downstaits plugged to the wall....and there was one time when the lines appeared on the screen...and then i turned off the heater, they would disappear.

If someone could help that would be great.....
Reply
Reply
post #5 of 21
4/25/07 at 1:38pm
You could also be getting coupling from AC power cables, too (especially if you've bundled all your cables into a "nice" package. AC power lines should never be put in the same cable bundle with signal lines. Also, any gaps in cable shields will allow the introduction of AC noise (which is what the moving horizontal lines are).

The quick (?) way to test that is to separate your cables and see if the problem persists. Also, some Cable providers have poorly grounded RF input coax (the feed to your home). Usually a RF isolator inserted ahead of your STB will solve this problem.
Reply
Reply
post #6 of 21
4/25/07 at 1:53pm
Quote:
Originally Posted by CT_Wiebe View Post

Also, some Cable providers have poorly grounded RF input coax (the feed to your home). Usually a RF isolator inserted ahead of your STB will solve this problem.

Beware of rf isolators for coax (cable) to solve ground loop problems. Improperly grounded coax (especially sat and OTA antenna) are severe safety hazards. Proper grounding will make the coax safe as well as remove ground loops (here proper means the way I gave in my first post). The safety issue is less important for cable when the mainlines are buried. above ground ones can be dangerous with lightning strikes.

Best,
jeff
Reply
Reply
post #7 of 21
4/25/07 at 2:12pm
Thread Starter 
Thanks to all.

Yes, it turned out to be a typical ground loop problem... As was stated above, even if you only see the horizontal bar when the scene is dark, it can be caused by a ground loop.

In my case it wasn't sat or cable related. When I plugged everything into the same outlet (using an extension cord) and the problem went away.

I'm going to do some electrical wiring this weekend

... Altan
Reply
Reply
post #8 of 21
4/25/07 at 5:43pm
Ok i took some pics so you guys could see my situation....im guessing its ground loop problem, but its never been this bad....this just happend yesterday they came out of nowhere. I took these pics like 10 minutes ago...still the same:







so if anybody could help..that would be great...im getting pissed that I cant see movies or play videogames at the moment because of this...
Reply
Reply
post #9 of 21
4/25/07 at 6:21pm
That looks bad.
Reply
Reply
post #10 of 21
4/25/07 at 9:14pm
Thread Starter 
Quote:
Originally Posted by MadMyers View Post

Thanks to all.

Yes, it turned out to be a typical ground loop problem... As was stated above, even if you only see the horizontal bar when the scene is dark, it can be caused by a ground loop.

In my case it wasn't sat or cable related. When I plugged everything into the same outlet (using an extension cord) and the problem went away.

I'm going to do some electrical wiring this weekend

... Altan

Alright... didn't work as well as I hoped. Everything is now on the same circuit. However, the line is there there (although it looks a bit different). The good news is I found it goes away if I disconnect the 3 inputs to my sat box (2 sats and 1 ota -- it's a DirecTV Tivo box with 2 tuners and OTA support).

I've searched for solutions, but all I find are solutions that apply to cabletv, not sat. Any suggestions?

... Altan
Reply
Reply
post #11 of 21
4/25/07 at 10:28pm
The cable tv solution applies to sat and to an OTA antenna. Youhave to ground the coax when it enters the building. That ground has to be bonded to the same ground you use for the house electrical system. If you don't you get a ground loop. If you don't do as above, then it's not up to electrical code.

If you sat is not grounded then you have a serious safety issue.

jeff
Reply
Reply
post #12 of 21
4/25/07 at 11:15pm
Quote:
Originally Posted by greeno View Post

Beware of rf isolators for coax (cable) to solve ground loop problems. Improperly grounded coax (especially sat and OTA antenna) are severe safety hazards. Proper grounding will make the coax safe as well as remove ground loops (here proper means the way I gave in my first post). The safety issue is less important for cable when the mainlines are buried. above ground ones can be dangerous with lightning strikes.

I had this driven home a few years ago while disconnecting a cableTV coax that was hooked up to a VCR that was connected to a monitor that had a 3 prong earth ground. When I disconnected the coax while touching the metal VCR, I got the **** shocked out of me. I measured 65VAC between the coax shield and the earth grounded monitor and VCR. 65V. I traced this to a severely corroded and paint encrusted connection on the earth ground connection at the house entry junction. Cleaning this up and getting a good mechanical as well as electrical connection mostly eliminated this but I still could measure about 7V at the far end of the run relative to the earth ground in that room. I also still had the faintest background hum on the audio if I cranked the gain that would go away if I disconnected the cableTV coax from the mix. I ultimately killed what was remaining by adding an additional earth ground to the cable coax shield via the closest splitter. You'll notice a grounding screw post on an all metalized coax splitter just for this purpose. I ran a connection under the house and connected to it to the nearest cold water pipe. Voltage differential was then less than 1 volt and any feint background hum was gone.

While safety ground eliminators, isolators, and cheaters can be effective in masking the effects of a ground loop potential, I agree they aren't safe and treat the symptom rather than the cause. If I was a little ol lady in my above situation, I may have fallen and couldn't get up.

Recently I had cable service turned on at a different residence. When I called about the status, they advised me that it was ready but since it used the houses existing coax runs, that may have been installed pre-code, they needed to come out and make a ground continuity measurement and inspection to verify safety code. 65V. Yea, I bet they are concerned about unsafe ground potentials on their networks exposed coax shields.

Dave
Reply
Reply
post #13 of 21
4/26/07 at 12:32am
You guys are right. The cable inputs to the house need to be properly grounded. The RF isolator should only be used to prevent coupling AC interference on the cable shield from getting into the system. The cable box and all electronics need to be grounded too.

Some problems arrise from miswiring in the house (outlets on different circuits and wired incorrectly). Other problems arrise from poor, corroded, connections at the outdoor cable distribution box. Older cable company wiring can be really bad.
Reply
Reply
post #14 of 21
4/26/07 at 5:54am
Thread Starter 
Quote:
Originally Posted by greeno View Post

The cable tv solution applies to sat and to an OTA antenna. Youhave to ground the coax when it enters the building. That ground has to be bonded to the same ground you use for the house electrical system. If you don't you get a ground loop. If you don't do as above, then it's not up to electrical code.

If you sat is not grounded then you have a serious safety issue.

jeff

Jeff, the strange thing is that my coax is grounded to the main house ground. There are 4 sat coax feeds from the LNB and 1 from an OTA antenna. They all connect to a grounding block, which has a wire going directly to the main ground. The main ground comes out below the main breaker on the outside of the house and goes down into, well, the ground, I cannot see a stake (buried?) , but it's about a 12 guage wire. The grounding block for the sat/ota is pressed up against this main ground with some sort of box with screw thingy (turn screw, tightly presses block ground wire against electrical ground wire)

Quote:
Originally Posted by CT_Wiebe View Post

Other problems arrise from poor, corroded, connections at the outdoor cable distribution box. Older cable company wiring can be really bad.

Claus, I was outside at 12:30AM with a flashlight looking at the grounding block. It does look like the screw used to attach the grounding wire is corroded a bit. I'll need to take a look in the daylight. Maybe this is the entire problem?

Any idea why it is corroding? Did the sat guys use a cheap block or is this just typical? The block is only 2 years old.

Thanks...
... Altan
Reply
Reply
post #15 of 21
4/26/07 at 8:09am
onavarro8, that is not a ground loop problem! It's either really bad interference, or a hardware problem with your display.
Reply
Reply
post #16 of 21
4/26/07 at 8:15am
Quote:
Originally Posted by MadMyers View Post

Jeff, the strange thing is that my coax is grounded to the main house ground. There are 4 sat coax feeds from the LNB and 1 from an OTA antenna. They all connect to a grounding block, which has a wire going directly to the main ground. The main ground comes out below the main breaker on the outside of the house and goes down into, well, the ground, I cannot see a stake (buried?) , but it's about a 12 guage wire. The grounding block for the sat/ota is pressed up against this main ground with some sort of box with screw thingy (turn screw, tightly presses block ground wire against electrical ground wire)



Claus, I was outside at 12:30AM with a flashlight looking at the grounding block. It does look like the screw used to attach the grounding wire is corroded a bit. I'll need to take a look in the daylight. Maybe this is the entire problem?

Any idea why it is corroding? Did the sat guys use a cheap block or is this just typical? The block is only 2 years old.


Thanks...
... Altan




Electronic components with faulty power supplies can cause electrolysis which can corrode and deteriorate ground connections and cause ground loops. If available use multi meter to check ac voltage between components and GOOD!! earth groound (sometimes only milli volts).

Roy
Reply
Reply
post #17 of 21
4/26/07 at 12:56pm
Quote:


Any idea why it is corroding?

For the most part, if you have a connection that involves dissimilar metals, a current flowing through them and air/moisture present, you have all the conditions necessary for corrosion or electromigration. The other key ingredient would be time.

As most of these connections involve mechanical compression, The materials and metals themselves will compress over time and what was once a tight, clean connection will get loose and dirty over the years.

When I first moved into my current residence, I was plagued by various electrical gremlins. Breakers and GFI would sporadically trip and ground noise was high. One day I inspected my breaker panel and noted that the house was wired with aluminum romex throughout and many of the connections to the breakers were somewhat loose. A little research into aluminum romex showed that it is notorious for compressing over the years not to mention that it is also a dissimilar metal connection. Simply re-tourquing all the connections at the breakers and select outlet boxes seeming cured all my gremblins and is one of the best tweaks I've made. I don't believe aluminum Romex is approved for new construction because of this safety and reliability issue and was grandfathered into the present code for convenience and expense reasons. I'd much prefer to see the whole house wired with copper romex but such a change wouldn't be practical.

My advice would be that if you're going inspect the coax cable connections, you might as well inspect with a wrench and screwdriver and make sure it's tight while you're at it.

Unless you know what you're doing, I wouldn't advise doing what I did on live AC circuits however. That may be best left to a qualified electrician.

Dave
Reply
Reply
post #18 of 21
4/26/07 at 6:49pm
Thread Starter 
Roy, Dave, thanks for the comments.

I'm beginning to pull my hair out. Let me summarize what I'm seeing and what I've done.

- Component output from HD Tivo (DirecTV) to projector has faint horizontal lines moving upward. Pretty hard to see... might never notice if you didn't look. But this is only a test setup. Below is the real configuration.

- If the component output from the HD Tivo is connected to my receiver (for switching) and receiver component output is connected to projector, faint horizontal lines become more noticeable. In the past I've put HD though the receiver with no trouble, so I'm sure this isn't a receiver bandwidth issue.

- HD Tivo has 3 inputs (2 sat, 1 ota). If I remove all three, problem goes away. If I remove less than 3, problem looks better but not perfect.

- Checked ground connection in circuit breaker for this circuit, it was tight.

- I've triple checked the ground block that the sat and ota coax use outside. It is good (I cut away old yucky ground, stripped it, and used this like-new part). Used DMM to check continuity between ground block and earth ground.

- Added new outlet. All equipment is on same 15 amp circuit (as a side note, I'm only at 12 amps, which is appropriate).

- For no good reason, I disconnected second DirecTV box from another 2 coax attached the ground box. No effect.

- Using the circuit breaker, I turned off any circuits with florescent lights or dimmers. Also turned off circuit to furnace. Made no difference. Lots of circuit were turned off at the same time.

!!! Ugh !!!

Here is what's left. The 3 coax (2 sat, 1 ota) that run to the HD Tivo are not single runs of RG6 quad. They were not long enough and have been "extended" using the coax thingys with male ends on both sides. I may be going crazy, but I am pretty sure I could see the horizontal lines get thicker and/or change speed when I moved these connectors closer together or further apart.

Does this make any sense? I'd prefer not the run new coax (to avoid the male to male connectors) ... if it doesn't make any sense.

Thanks again

... Altan
Reply
Reply
post #19 of 21
4/26/07 at 8:11pm
As a trouble shooting aid, you could try connecting a temporary earth ground (12 ga or so wire) to the nearest or common earth ground (3rd prong on nearest outlet or nearest copper cold water pipe) and temporarily touch it to the conductive part on the coaxs f-connectors or metal binding nuts. If your situation is like mine and others- With a voltage potential existing between the coax shield grounds vs the houses safety earth ground being the cause of ground loop problems, this extra path should reduce that voltage potential and you should observe a reduction in the problem. As I noted, in my particular situation, the house entry ground was not stiff enough on it's own to clamp the potential and totally eliminate the problem. A second ground tie point at the end of the runs did it.

If you try this, make sure you get the temporary test wire connected to the nearest EARTH SAFETY GROUND. Not the Hot!!! Since you have a DVM and seem comfortable using it, measure the AC voltage between the temporary test earth ground and the disconnected coax shield to verify there isn't a dangerous voltage potential present. If you don't measure more than a volt of potential, you may be barking up the wrong tree and your problem isn't related to the coax being interconnected in the mix.

HTH

Dave
Reply
Reply
post #20 of 21
4/27/07 at 7:30am
Is your antenna and dish mounted on a metal plumbing vent pipe? If yours is like mine all feeds come from antennas mounted on common vent pipe and this might be source of problem. Also if you still have a regular receiver hook it up and bypass tivo. Things like this require eliminating one thing at a time.

Roy
Reply
Reply
post #21 of 21
4/28/07 at 7:36pm
Quote:
Originally Posted by JohnnyG View Post

onavarro8, that is not a ground loop problem! It's either really bad interference, or a hardware problem with your display.

Those purple lines dissapeared like couple days ago but it was really wierd,
Yea I was thinking that it might be something else. It is definitley not my projector so im guessing its my receiver, I have a really old Denon receiver and the audio is already getting some problems......I will have to take it to get it fixed/replaced...
Reply
Reply
New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Display Calibration

AVS Top Picks

AVS › AVS Forum › Display Devices › Display Calibration › Ground Loop Question / Assistance