White Line in Video Output

[stevech]

that one, to me, looks like a classic hum bar.
causes:
1. broadcaster's problem. Unlikely
2. video cable with bad shield or connector or corroded connector shell
3. ground loop between devices on either end of a video or RF coax. Usually when the two devices are connected to opposite AC power phases as in a 110V home (in the US, all homes are two phases).
4. Video device with faulty power supply that induces hum

[AWS]

I just found my hum. My Simplifi amplifier's SUB OUT RCA connector was loose and not making a ground connection (on the inside of the amp). Found it by error by plugging in a new Monster Cable from it to the sub.

I'll return the amp for replacement. In the mean time I've put a 22(ish) gauge, shielded wire wedged between the male RCA connector of the wire against the RCA female connector of the amp. Then ran the other end of the wire to the built-in ground screw of the cable 2-way splitter.

No more hum


AWS

[jtshea]

Originally Posted by stevech

that one, to me, looks like a classic hum bar.
causes:
1. broadcaster's problem. Unlikely
2. video cable with bad shield or connector or corroded connector shell
3. ground loop between devices on either end of a video or RF coax. Usually when the two devices are connected to opposite AC power phases as in a 110V home (in the US, all homes are two phases).
4. Video device with faulty power supply that induces hum

Thank you. Now that I know what to call this problem and I've been able to look at other examples on the web, I know this is my issue. I've heard of ground loops before, but I didn't realize how it could affect video.

The only connections into my PC are AC, coax, powered speakers, monitor, and network. I've already tried taking the network out of the equation. The speakers are two-prong and so not grounded. The monitor has the same ground as the PC. So, it seems my best bet for a fix will be to isolate the coax.

I just ordered this cable isolator.

This product seems to be recommended too.

Ground loop seems to be a common video problem. It doesn't speak well of ATI support that 2 or 3 different techs looked at my screen capture and did not identify this.

[stevech]

The product links, above, are for coaxes with RF, not composite video. RF, as in cable TV coax. They won't pass composite video.

I and others deal with ground loop problems as follows... not safety-endorsed by UL, I suspect.

I have a PC in the garage which feeds video over a 50 ft. coax to the LR TV. That TV and the PC are on different AC phases, due to the way the breaker box is setup. I could change which breaker feeds the PC, but I chose not to muck about there.

So, the cure is to "lift" the ground connection on the PC's power cord. I do this with one of those adapters intended to allow a three prong power plug to go into an (old) two prong outlet. So the PC's power cord's ground pin dangles, unconnected. And you must do so for any PC peripheral connected by USB or RS232 or whatever, where it uses a 3 prong plug. Or plug them all into a power strip and float (lift) the power strip's ground.

This eliminates the ground loop.

You can also purchase a device called a "Hum Bucker". This is a 4 inch cube with two BNC coax connectors. You run your video through this. It is a notch filter for 60Hz (US power). I have one and it does not help the ground loop problem. What it can do is reduce hum that is induced into the coax due to a long coax run where there are strong AC fields. They're common on movie sets due to the lighting cables.

[jtshea]

Well, that got me thinking. If a tuner card was using coax (for tuning analog cable) and also had a composite connection (for video in from a VCR or whatever) you could potentially have more than one ground loop in the PC.

The first ground loop is caused by two different grounds in the tuner card: one from the coax and one from the AC into the PC. If the tuner card doesn't isolate one of these grounds, you've got a ground loop. (Perhaps this is why I see the problem on the Sapphire Theatrix 650 but not on the Hauppauge HVR-1600? Better cable ground isolation built-in to the Hauppauge?)

The second ground loop is caused by the VCR following one path to ground, the PC following another, and the grounds of the two devices being linked together via the composite cable (thus completing a loop and giving each device two grounds).

Personally, I'm going to try a cable isolator device. It passes the RF signal magnetically, but does not pass the current that is causing the interference. I believe there are similar devices for composite connections. I just don't want the risks that go along with "lifting" the AC ground via a 3-prong to 2-prong AC adapter.

[jdamore]

Originally Posted by stevech

So, the cure is to "lift" the ground connection on the PC's power cord. I do this with one of those adapters intended to allow a three prong power plug to go into an (old) two prong outlet. So the PC's power cord's ground pin dangles, unconnected. And you must do so for any PC peripheral connected by USB or RS232 or whatever, where it uses a 3 prong plug. Or plug them all into a power strip and float (lift) the power strip's ground.

What are the dangers in lifting the ground? If the device malfunctions, is it plausible to get a shock? Or is that just a myth?

Thanks

[jtshea]

Here's a good article on Howstuffworks.com that explains the risk of lifting the ground.

http://electronics.howstuffworks.com/question110.htm

Key point:

The idea behind grounding is to protect the people who use metal-encased appliances from electric shock. The casing is connected directly to the ground prong.

Let's say that a wire comes loose inside an ungrounded metal case, and the loose wire touches the metal case. If the loose wire is hot, then the metal case is now hot, and anyone who touches it will get a potentially fatal shock. With the case grounded, the electricity from the hot wire flows straight to ground, and this trips the fuse in the fuse box. Now the appliance won't work, but it won't kill you either.

What happens if you cut off the ground prong or use a cheater plug so you can plug a three-prong appliance into a two-prong outlet? Nothing really -- the appliance will still operate. What you have done, however, is disable an important safety feature that protects you from electric shock if a wire comes loose.

[jtshea]

I just came across some more information that I thought I should add to this topic. There are other possible causes of audio hum or video hum bars besides ground loops. These probably aren't as common or as likely, but I thought I should share these for anyone who is interested in this topic.

http://www.epanorama.net/documents/g...erhumming.html

[jtshea]

I did more troubleshooting. Still no fix. My problem does not seem to be a ground loop. I've got a few more things to try. Maybe you can help me prioritize or point out some other things I should try. Here's a recap:

Ground Loop - No
Tried 3-prong to 2-prong adapter to isolate the ground on the PC. (By the way, I would never do this as a permanent solution for safety reasons.) No change. Tried cable isolator device. No change. Only connections into PC that could cause ground loop are coax and the AC. There are no composite cables or other connections leading to other grounded devices. The white bars are not accompanied by audio hum. Also, they do not roll up or down the screen. They stay in essentially the same position and randomly rise and fall by about an inch. They are apparently caused or influenced by a slightly varying electric or frequency level coming from somewhere. Also, they only appear on certain cable channels (17, 18, 19, 24) and only on the Theater 650 based video cards.

Software Problem - No
Have tried SageTV and also ATI MMC. Same on both. I believe DirectShow is part of the tuning for both of these. Tried tweaking the tuning with FreqShifter with no improvement.

Bad Tuner Card - No
Tried an ATI TV Wonder 650 in addition to Sapphire Theatrix 650. Same problem shows on both.

Tuner Card Incompatibility With PC - No
Bad Power Supply - No
Tried card in another PC in the same room. Same problem.

Problem On AC Circuit - No
Ran extention cord to another circuit. Same problem.

Problem On Cable Path - Maybe
Need to check this out. I've tried connecting the tuner card directly to the main cable antenna, but ultimately it is the same path through the wall, etc. I need to try running a line from a different part of the house, or try moving the PC to a different part of the house.

Problem With Nearby Transformer - No
Shut off heating / cooling system at breaker. Unplugged all wall transformers for router, etc. No change.

Problem With Bad Transformer Or Power Supply Somewhere Else In House - Maybe
Need to check this out, but man what a pain this will be!

Cable Signal Too Low - No
Tried connecting tuner card directly to main cable line. Tried signal booster. No change.

Cable Signal Too Strong - Maybe
Need to check this out. Doesn't seem likely, as card was originally fed by a branch off a 3-way splitter. This would have attenuated the signal a lot.

Why am I putting so much effort into this tuner card? This card has the best picture quality of all the ones I have tried. Ultimately, if I have to, I'll just live without recording the affected channels with this card. However, these white lines I am seeing are not normal for this card or other folks would have mentioned it by now. So there must be a fix in my particular situation.

[Razillian]

jtshea,

One thing I didn't see in your post is internals of the sage box. It could be that another device inside the computer is producing enough of a RF Field (induction from any number of sources) that your tuner card is picking that "hum" up. Only reason I bring it up as a possibility is that I have seen this with audio cards when dealing with high quality microphones. The "better the quality" of audio card, the more likely it would pickup electrical noise and mess with my audio operations (better quality cards tend to have more circuitry, which means more copper lines, which means they act as a longer antenna).

Your likely culprits making the electrical noise are fans, the powersupply, or high end video cards that require a seperate power source. You could try moving the capture card to a different PCI slot so it is inbetween other PCI cards that are not likely to produce a signal (or as powerful a signal), or throw the capture card in the farthest slot so it has the case on one side of it, and strap on a thin aluminum plate to the other side, with a ground connection to the plate (very carefully to avoid any possibility of a short).

[jtshea]

Thanks for that. I did try the card in two different PCs and kept seeing the problem. That doesn't completely rule out RF issue, but it means the problem isn't unique to the equipment in one particular machine.

But your point about better cards being more sensitive to noise got me thinking. I spent some time watching my problem channels on other SD TVs in my house. It is very subtle, but I think I am seeing indication of the same problem. So, now I'm back to thinking about noise on the cable antenna.

I may yet try some homebrew shielding as you suggested, however.

[Razillian]

What's funny is that now that you notice it on the other normal non-sage tvs, it will drive you nuts when you watch those. Ok, maybe funny in a maniacal laughter kind of way.

Being to lazy to reread all of this thread, but have you tried something like this: http://www.21best.com/21_best/electr...ale_.html#CATV ?

[jtshea]

I tried one cable isolator (this one http://www.elect-spec.com/video.htm) but the quality of the device was poor and so the results were inconclusive. I may yet try the VRD-1FFj, but I've got to do a little more testing first.

I've got a multimeter now, and I'm going to try to verify that I've actually got a ground loop. There are some procedures here:

http://siber-sonic.com/electronics/GLooptest.html

[jtshea]

Something just occurred to me. In the process of testing, I ended up moving some things around. At the moment there is a Sapphire Theatrix 650 and a Hauppauge HVR-1600 in my PC. The cable antenna now has a splitter on it to feed the two cards. I can still see the white line problem on the Theater 650, but it is not as bad. I'm excited that I somehow influenced the problem, because this means there's hope. I have a theory that I need to check out.

I've been doing so much testing and tuner card swapping that I didn't bother to screw the cards down in the PC case last time. My understanding is that this is how PCI cards get grounded. So, if the card is not screwed down tightly, the ground connection may weaker, and any ground loops would also be weaker. This may be an indication of a ground loop.

[Razillian]

Originally Posted by jtshea

So, if the card is not screwed down tightly, the ground connection may weaker, and any ground loops would also be weaker. This may be an indication of a ground loop.

It may also be an indication of RF interference being picked up by the card itself. The grounding of the card might be shunting some of the interference. Every wire is an antenna acting as a receiver, the length of the wire determines what frequencies and how well it picks up transmitted signals. Every wire with a current flowing through it is a transmitter, and there are a lot of wires with power applied to them throughout a computer. Food for thought.

[SHS]

jtshea can give me full run down on how everything hook.
How min TV in house are still hook up to cable system?
Is that sage box hook to reg TV and dose that TV have a coax hook up?.

jtshea you said you tested the Theatrix 650 in a diff PC but was that PC on same Circuit Breaker or even the same Power Circuit Line.

Have try testing a VCR by using VHS tape?.
You know it possable that the problem your have is with in the card it self maybe it just a bad card.

[jtshea]

I appreciate everyone's efforts to help. I've learned a lot in the process. I believe I've taken the testing and process of elimination as far as I can with the time that I have available. So for now, I'm living without recording the affected channels on my PC. The picture on the Sapphire Theatrix 650 is so beautiful on the other channels, that it is still worthwhile.

My gut says the problem is coming in on the cable from the street or it's being induced into the cable or the AC lines by something local. I think I've pretty much ruled out anything that could cause a ground loop.

I've tried another Theater 650 card and saw the same problem, so I know it's not a defect just in my tuner card.

There's a bunch of other things I could try (like actually moving the PC to another room, or trying it at someone else's house) but I just can't right now. I should probably even post a video clip. But again, free time is an issue.

So, I think I'll let this issue drop for now. If I find some more time for testing, and I discover something that I think will help others, I'll report back here.