Bad Coax Run?

[4528140000]

Hi,
I just ran all new RG6 quad shield cable during my house remodel (8 dedicated runs, much effort). I'm only using 4 of the runs. Now one of the cables is delivering very poor quality analog video (very pixelated). The other two runs I've been able to test are OK. I've disconnected the splitter and run directly to this room and tested a separate TV on it. Still bad (so I know it’s not the TV). Although it did get slightly better when I removed the single 1-to-4 splitter as the cable enters the house (there are no other splitters). I assume I have a problem on this one run, but one of the "good" runs also takes a similar path, so I don't think it's a problem with being near any romex, or phone wires, etc. If you're troubleshooting a single run (that you don't have full access to), where would you start? Any hope that it would be in the end connectors? That would be easy to fix, but those were pretty simple to put on, so I don't imagine the problem is there.
Thanks for any advice, -- Mark

[jdc2000]

If the problem isn't in the end connectors, then it is likely one of two things.

If the cables were not run through conduit, then it could be a staple, nail, or something else that punctured the cable. Or, it just could be a bad section of cable.

[4528140000]

I didn't specifically find the problem, but what I did that may help other people. First I bought an $88 Paladin tester at Menards (local big box hardware store) and tested the cable in question. It failed for a "short" (damn). So, I decided to replace each end connector because I noticed during installation that it's possible to leave a single strand of shield braid wrapped around the center conductior if you're not careful. I didn't see anything like that, but figured I would try anyway. Unfortunately, that did nothing.

After that I was down having to replace the cable. The really bad part would be the section that is buried within drywall. I decided to cut the cable in the basement suspended ceiling where it comes out of the drywall and put connectors on both new ends and test the two sections. That would allow me to isolate the short in either the drywall section or the basement ceiling. I did that and the section in the drywall tested good (thank goodness) and the section in the suspended ceiling tested bad for a short. Since the section in the ceiling is relatively easy to access, I just replace the whole section, then used a male-male connector to connect the new ceiling section to the existing good drywall section. Took a while to run the new cable, but it now works great.

I strongly suspect a bad section of cable, since no work was done near the cable in the ceiling and I was meticulous when I secured the cable with the proper coax cable holders.

Lessons: 1) when running new cable that is going to get covered up, put some ends on it (even if you have to snip them off later) and test it before drywall goes over it.

2) If you have a failed cable, cut into it at a convenient location and use a tester to isolate the bad section to one half or the other. At least then you don't have to pull an entirely new cable.

3) If you need to choose the cable to cut into from amongst a bundle of cables do this: Buy a $10 electrical circuit proximity tester (or whatever they are called). This is a pen-sized device that will beep or flash when it is touched to (or near) a 110v (or higher) circuit that is live. You do NOT have to have anything running on the circuit for the tester to work, just electricity "available" (a potential). Next, tape up one end of the problematic coax cable so it can't touch anthing that will conduct electricity. Then go to the other end and strip off an inch of insulation and shield and stick that end into the hot slot of an extension cord. That will create a potential in your coax cable, but don't worry -- there is no circuit, so no electricity is actually "flowing", so you don't have to worry about heating, melting, etc. Now go touch the circuit tester to each cable and see which one sets off the tester. If the cables are very close to each other, more than one may set off the tester, but you'll notice that the response is much stronger in one cable (non-interrupted beeping or flashing versus intermittant on the others). That's your cable to cut into for testing. MAKE SURE YOU DISCONNECT THE ELECTRICITY FROM YOUR COAX CABLE BEFORE YOU CUT INTO IT.

Hope this helps somebody.
--Mark

[fink]

Thanks for the update. Glad you got it sorted but I have to say that your no 3 solution isn't exactly standard, safe industry procedure. There are cable testers available that can test rf (and other types) of cable using very low electrical signals for shorts and continuity and lots of other useful info as well (like distance/length, impedance etc). they're a bit pricier but there would be no risk accidental electrocution by sticking the core wire of an rf cable into an electrical socket. That would probably be illegal in many countries and if a fire started or accident happened would likely void any insurance policies as well.

[4528140000]

Fink,

I agree -- my solution of plugging the coax into 110v to find the cable I want amongst an unlabled bundle is not ideal and potentially dangerous. However, I was desperate, and it actually works quite well if you're cautious.

I would only use this method if you don't have better options.

--Mark