Troubleshooting Ethernet Cable

gravtyklz

I have three ethernet cable runs, two work and one doesnt.

I rewired the 3rd thats not working twice now to make sure I did it right. It still doesnt work at all. At one end it's connected to a dsl modem.

On the other end its first wired to a ethernet jack, and then a cable between the jack and the computer. I've used the cable that goes between the jack and the computer at all three location so I know that cable works.

Are there any tests that I can do on this cable run with an ohm meter? If not what do I need to do to test it?

JohnJ0906

I'm no expert, but try changing the jack. Have you swapped wires on the modem? (Assuming all 3 go to the modem)

Just a couple things to try, before buying a tester for this.

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John from Baltimore
"One Day at a Time"
All replies based on the 2008 NEC

GregS

You need a continuity tester for RJ type jacks. Plug a relay(?) in one end and a tester in the other. It will tell you if all the pairs are open, or short or crossed.

Test-um generally makes some inexpensive stuff. You can even find something at Home Depot.

Are these crimped ends or punchdowns into a jack?


Can you see the entire cable end to end, or does it go through a wall? Could it possibly be pinched or stabbed somewhere that you cannot see it?

Kgmz

There are a few simple things you can check for before you buy a tester.

But, did this cable run ever work before, or is this a new run that has never worked.

I am assuming this is a in wall run with female jacks on each end with patch cables running to components.

Check the jack ports with a flash light. I once had a problem like this and it ended up being two of the spring wires in the jack where the external cable plugs in were crossed. They had popped out of their slots somehow.

Now for a basic test of the wire run to check for breaks in the wire with a ohm meter. Just disconnect the jacks at the ends of the run. Twist the pairs together at one end, i.e. blue/ blue-white together, orange/orange-white together, etc. Then go to the other end and test each of the 4 pairs, if you have continuity for each pair then the wire is fine and the problem is with the jacks or it is miswired.

A W Smith

you probably need a crossover cable pin out.

http://www.homenethelp.com/web/expla...-crossover.asp



http://www.ertyu.org/steven_nikkel/ethernetcables.html

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Al Smith
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gravtyklz

Well I wired all three of these cables the same way. and I rewired this bad one twice to make sure that I wasnt using a bad jack or male end piece (maybe incorrect terminology here?)

I wired it using the T568B method on both ends. It does need to be a straight cable as it will be going into either the dsl modem directly or a switch.

Theres only about 30" of the cable that cant be seen. It's behind drywall at that point.

This is my sisters house, I didnt run any of the cable so I'm assuming that it just goes straight down since I can see it down in the basement about where this room is.

At the end where the modem and switch are I used a male connector, and in the room where it will be used I wired a female jack into the wall. I used the B method for both ends like I said, and i've compared them to the work I did in the other two rooms and they are identical.

I think i'll do some continuity tests today, and if i'm still stumped I guess i'll buy a tester. If I buy too much I'm gonna have to get some IT/Low Voltage training and start doing this more often.

A W Smith

Is it an older house? We had a mice problem and the damn things ate my ethernet cables above the kitchen and dining room ceilings. One day our bedroom ethernet runs just stopped working, Opened the ceiling to reveal ethernet wire completly stripped of its jacket and bare copper in spots. Fixed the mouse problem and ran a few new runs. Went hybrid/wireless recently when i bought my wife her laptop. Maybe you should consider that.

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gravtyklz

This is new construction, they just closed on it last week. I told them that wireless may be the best option anyways since it is a laptop that they want to use in that area in any case. But there is still the pride of wanting to have everything in a new house actually work just for the heck of saying it works.

A W Smith

if it is new construction and never worked to begin with then it could be a cut Ethernet cable of an over driven staple. have you brought the laptop to the modem and used a known good cable in the same port the troublesome cable is in? some modems have a crossover pin-out on the port itself which precludes the use of a crossover cable. have you checked this? If you have a continuity tester just do as Kgmz suggested above and twist the four pairs together and test continuity at the other end on each pair.


Edit to add
are you getting a yellow or green or no led light on your device ?

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Al Smith
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gravtyklz

The led light isnt coming on at all, not on the modem and not on the laptop. I dont think it has a crossover pin-out on the modem....it came with a straight cable to be used, and I wired the other two lines straight and they work fine. I'm gonna head back over there in a little while today to try testing the continuity.

Dustball

I use a basic tester very simlar to this one to do my ethernet cabling testing-

http://www.newegg.com/Product/Produc...82E16899997005

You may be able to find one at your local home improvement store if you need it now.

gravtyklz

Okay I just did that, and the Orange cable is the one thats the problem. I couldnt tone out the Orange/white orange pair so I toned them out with different wires to narrow down which one of them are messed up.

I looked at http://www.ertyu.org/steven_nikkel/ethernetcables.html

It says that the Blue/White Blue are unused. Could I use one of these instead? That sounds too good to be true though.

A W Smith

yes

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Al Smith
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gravtyklz

Not sure if you were saying yes thats too good to be true, or yes it would work. In any case I gave it a try.

All I did was switch the Blue and Orange. It connects and both led lights stay lit. I still cant get any network connectivity though.

gravtyklz

Never mind that...I pulled the orange off of the jack all together and its all working now. I learned a thing or three today.

Thanks a lot for all the help.

TPnTX

did you switch the blue and the orange as pairs? You want to keep it as pairs .

the pins used in ethernet are 123 and 6. so if orange and blue are used
1---- 2--- 3-------- 6
w/o o/w w/bl----- bl/w

if you use another pair be sure they are using the correct pinout or you won't be at cat5 level.

ProCom

Pinout for 568B is 1 w/0, 2 o/w, 3 w/gr, 6 gr/w

blue pair is pins 4 and 5

BriansZ

It would be good practice to wire all four pairs, not just the tx and rx. While data only uses pins 1,2,3,6, other technologies such as PoE may require the unused pairs.