Cable causes interferance since moving Tivo

karlhafen · 06-15-2008, 10:51 PM

I recently did a remodel at my house and moved my s2 to a different location. The Tivo is located in a closet and connected via a 25' s-video cable. My problem is now whenever I have the cable tv hooked up it really messes up the Tivo's output. I can unhook the cable and watch pre-recorded shows just fine. If I hook up the cable I can not even watch recorded shows.

I also have a Tivo HD in the same closet(feeding a different tv)I can hook it up (to s2's tv)via 25' component cables and it works but does have some interference as well. I don't think that the cables are a problem. I have a ROKU Netflix player hooked Via the 25" component and it is clear.

Any ideas?

chip_r · 06-16-2008, 06:56 AM

So, to summarize, hooking your cable TV cable to either Tivo causes it's output to mess up for both previously recoded shows and newly recoded shows. With no cable TV cable attached, the outputs are fine for older shows. ROKU has no problems.

It's a grounding problem between your cable TV cable entry point, Tivos in the closet and your TVs. The ROKU doesn't exhibit the problem because it doesn't involve your RF cable.

Putting a long distance between your Tivos are TVs can be an issue itself but let's put that aside for now. You didn't mention if you also connected cable TV directly to your TVs because that could complicate things further.

Try the following experiments:

1) For your S2 and it's TV, use an extension cord and connect the TV's AC input to the SAME AC outlet as the S2 Tivo supplying video signals. Unplug all video cables from the Tivo HD and other set to get it out of the equation. Ideally, you could move the TV next to the S2 and use the same AC outlet and short video cables. See if this helps.

2) Repeat 1) but with the Tivo HD and it's TV. Remember to unplug all video cables from the S2 to get it out of the equation.

In both cases, check with and without attaching your cable TV cable to your Tivo. I suspect that your picture will be OK, maybe not perfect, but better.

If indeed this fixes the problem with the longer S-video and component cables stiil in use, you can get an RF isolation transformer to connect right before your Tivos. Something like the Calrod isolation transformer at the bottom of this page or similar. An isolation transformer breaks the grounding between the CATV system and your home.

If the test with the AC extension cord doesn't fix the problem, then definitely move the TV next to the Tivo and connect AC and video cables directly (no long cables). This should mimic the case before you did your equipment re-shuffling. Make sure you're OK in that setup. If it's clean, then use your longer 25' cables and see if that's the grounding culprit. I've got suggestions on that front but let's not go down that route until a AC grounding is completely ruled out.

Other things to check are 1) Make sure your CATV is grounded at the entry to your home. Your CATV provider should have a ground wire between their entry point and a cold water pipe or other earth ground. 2) House wiring. The Tivos and TVs could be on separate circuits in your house and those could have a grounding problem.

See how far this gets you and comment on any findings.

chip_r · 06-16-2008, 08:41 AM

I re-read your post a bit and (I assume) the Tivo HD and it's TV doesn't exhibit any problems at all . If so, still do step 1) because it's likely grounding between the CATV entry, closet, and S2 TV.

One other check comes to mind if it's a house wiring thing ... reversed line/neutral or a missing ground wire on your S2 TV outlet or closet outlet can also be the culprit. If connecting your S2 TV to the same outlet as the S2 fixes the problem, then run down to Home Depot/Lowes or the sort and pick up an AC line tester. It's a 3-prong plug with some indicator lights. After plugging it into your S2 TV or closet outlet, read off the indicator pattern. It'll tell you if your house wiring is normal at the outlet or it found a problem. They're around $10 or less if I recall.

karlhafen · 06-17-2008, 09:30 PM

I tried an extension cord to the tv's plug and the problem was still there. I used a multimeter to see if both room's plugs were wired correctly. The polarity was correct but the closet was missing a ground. Tried adding a ground and the problem was still there. The tv uses a computer type power cord. I had an extra cord so I broke the ground pin off one and tried it on the TV and the problem was gone. I realize this is a bandaid and I need to fix the REAL problem. Any good ideas?

chip_r · 06-18-2008, 05:48 AM

Sounds like a house wiring issue and you're correct in wanting to fix the real problem. By breaking the ground pin off, you're floating your TV hot and neutral and eliminating a ground path. The shield of your cable TV cable is usually chassis ground (and earth ground) so that's why it's related to your cable TV. The component and S-video cable grounds may be isolated from the chassis but if not, 60Hz removal is much easier and more effective by your TV for those signals.

You said you used a multimeter to check wiring but you really can't check for a hot/neutral reverse or a broken ground back to your breaker box. Other combinations can also exist and can be just as hazardous. Even though you've added your missing ground in your closet, that won't fix a hot/neutral problem elsewhere. Just because an outlet works, doesn't mean a contractor or previous owner wired it up correctly (and safely). I've found a couple of goofy shortcuts and mistakes made by the previous owner in my house with my tester.

This is the AC outlet tester mentioned earlier. If you look closely at the picture, it checks for all combinations of wire swaps. A multimeter can only check for some of the problems. HD, Lowes, or most hardware stores have them locally.