strange result from network tester

[ZippyDan]

I'm using a cheap network tester (like this one but Sperry brand http://www.amazon.com/TRENDnet-Cable.../dp/B0000AZK08).

The cable tests "good". All four lights light up green in order. HOWEVER, there is the tiniest flicker of red between each flash of green. It seems to be coming from INSIDE the device (probably it would be more accurate to say the light is going red for a picosecond so it looks like it is coming from inside instead of being fully illuminated). The flicker of red is so faint, that I can only really see it with the (room) lights off.

I have tested with other known good cables (with the lights off), and this miniscule flicker does not happen.

Furthermore, when I use this cable to connect some switches, nothing lights up on the switches (no connection is recognized).

But here is the really frustrating part: that cable was working fine for more than 2 years. I just cut it to move its termination point and I put on a new termination. The problem only started then! So obviously it must be my new termination, right?

I tried the termination two more times and it still failed to successfully connect the switches and the tester still shows the slight flicker of red.

There is a splice in the cable at an easily accessible point, so I removed the splice and test the cable there. From the splice to my new termination: NO PROBLEM. From the splice to the other end: red flicker. That means my new termination tests FINE and should not have anything to do with the problem. But then why did the problem only start when I cut the cable? ARGH.

Why don't I just replace the cable? Sigh ... well the "other end" (the side I did not cut) is on the other side of a 85 foot run through underground conduit (the cable is rated for outdoor burial). It was a pain in the ass to get it out there in the first place and it has worked fine for 2 years. Any one have any ideas what could be causing this?

 

[Mushkins]

Break in the cable somewhere. Could be something chewed/burrowed through your conduit and damaged it, or water seeped in somewhere. Could be inside the jacket and was weak to begin with for whatever reason, and you futzing with the cable was the straw that broke the camels back.

Or the far end was damaged in some way, maybe it wasn't terminated properly to begin with or something tugged it loose/damaged the termination. I'd try re-terminating the far end and retesting.

Im assuming this is twisted pair and not coax? I really hope you didn't splice twisted pair :/

 

[ZippyDan]

Break in the cable somewhere. Could be something chewed/burrowed through your conduit and damaged it, or water seeped in somewhere.

Or the far end was damaged in some way, maybe it wasn't terminated properly to begin with or something tugged it loose/damaged the termination. I'd try re-terminating the far end and retesting.

Im assuming this is twisted pair and not coax? I really hope you didn't splice twisted pair :/

Yes it is twisted pair cat5e. I used "splice" loosely. There is a coupler in-line with the run, near where the outdoor cable enters the main building and that is where I did more testing.

The cable is water-"proof" but ... eh, ok

I'm still wondering about the strange all-green result with tiny red flickering ha

 

[jaqie]

quite simply you either need to dig it up and inspect it or get more advanced testing gear.

If the gauge of the cable is known and you have a very accurate ohm meter, you can figure out about how far from the end the cable is broken. Phone companies do this on copper lines to cut down drastically on the service time required.

 

[Mushkins]

Yes it is twisted pair cat5e. I used "splice" loosely. There is a coupler in-line with the run, near where the outdoor cable enters the main building and that is where I did more testing.

The cable is water-"proof" but ... eh, ok

I'm still wondering about the strange all-green result with tiny red flickering ha

Ok, an actual in-line coupler is much less cringe-worthy My mind had visions of handmade twists and a rats nest of electrical tape.

Yeah, the flickering points my first guesses to a bad/weak/damaged termination on the far end, or one of the copper wires inside the jacket was dinged or snapped but is still mostly making good contact just from pressure. That could be from someone bending the cable a bunch before installation or who knows what. Either way, you've traced the issue to that end of the cable and not your recent work.

 

[ZippyDan]

quite simply you either need to dig it up and inspect it or get more advanced testing gear.

If the gauge of the cable is known and you have a very accurate ohm meter, you can figure out about how far from the end the cable is broken. Phone companies do this on copper lines to cut down drastically on the service time required.

If the cable is broken, why do I get green on the LAN tester?

I have a Fluke 117, but I don't think I could get the two leads to the opposite ends of an 85 foot run

 

[jaqie]

You run a loop of the wire.
Your fluke 117 is nowhere near accurate enough to do what I am suggesting, anyway.

LEDs do not require high frequency signals to power them. I could get into HF signal skinning and attenuation, but I don't think it will do much good.

 

[ZippyDan]

in the end, we ran new cables and everything is working fine now.

i still get the strange red blinking from the tester though, on these two cables and no others. the cables are brand new and so are the terminations, so I'm thinking maybe it has something to do with the length of the wires, since no other wires in the office are even half as long. maybe something like the tester thinks the signal allllllmost times out and then it gets the response. dunno

 

[John Connor]

I think it's the length of wire too. Is the battery in the tester good? A rechargeable battery doesn't have the same power output as a regular alkaline battery.