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Discussion Starter · #1 ·
I apologize ahead of time for the somewhat basic question; I have run every search on the forum, but I am legitimately confused and wondered if I could get a quick answer here....


Here's my current setup before adding receiver, etc. - SA 8000HD set top box connected to display via component cables. Both the STB and display running through the same surge protector. I am getting scrolling diagonal lines on nearly any channel, SD or HD. I tested an upconverting DVD player using the same power outlet, component cables, and input to the display. No diagonal lines, no hum bars, nothing - perfect picture.


So, I think this is a ground loop issue. Here's my issue - even when I disconnect the coax from the STB, the diagonal, hum bars remain. Obviously, when I disconnect the component cables to the display, we're good again - no input to the display.


Is the problem at the coax level or the component level? Will a Jensen Cable RF Video Isolator work in this instance, or do I need a video isolator that runs through the component cables? I know this is probably easily answered, but I am clearly not an A/V expert and I've searched this forum in vain, unfortunately.


Any ideas here?
 

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Discussion Starter · #3 ·
Tried separating them as much as possible, but no effect. The problem is clearly with the set top box or coax line, I would assume - I just would have thought that removing the coax from the STB may have eliminated the hum bars if this were truly a ground loop issue. What am I missing here?
 

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I had a bad STB once that I had to swap in for a new one. I would try hooking the cable to the back of another tv, if you have another to test with.


Edit: that is if the cable will show anything without the STB in the mix.
 

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Sometimes, hunting down the source of a 60hz video hum can be a tremendous pain in the rear.


Sometime in the next couple of weeks I'm going to start adding a chapter to my Dedicated-HT thread complete with pictures and I'll be asking the entire forum to help me hunt down a hum very similar to the one that you are describing.


I've already been to DBSTalk and a few other places, and I've already done some basic outlet/ground testing.


One thing I've learned from talking to those with experience is that the source of your hum could be in the least likely place. One guy told me a story of a company that could not get the video hum off their monitors. The hum persisted for years, and they finally called in an expert to correct it. It turned out to be the power cord to a projector that had somehow been wired backwards.
 

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Plug the projector into an extension cord and test it in a different outlet.
 

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Quote:
Originally Posted by bfoster /forum/post/0


Diagonal lines sounds more like an intermod beat than AC hum. AC hum generally presents itself as horizontal bars scrolling through the picture.

Good catch. I missed that detail.
 

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Discussion Starter · #9 ·

Quote:
Originally Posted by bfoster /forum/post/0


Diagonal lines sounds more like an intermod beat than AC hum. AC hum generally presents itself as horizontal bars scrolling through the picture.

Any methods to remedy the intermod beat if that's the problem? I guess the issue could be a faulty STB (just assumed ground loop based on the descriptions I had read) - I likely need to try the STB elsewhere, as a DVD player connected to the same power source and component input showed no visible banding.
 
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