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Wireless Networks Thread, Cable Problem in Technical; I have an ethernet port in a classroom which stopped working - no computer could connect to the network or ...
  1. #1

    witch's Avatar
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    Cable Problem

    I have an ethernet port in a classroom which stopped working - no computer could connect to the network or the internet or anything. My cable tester showed no issues though.
    As the faceplate had been pushed in and the catches broken, I have had it replaced and the wiring checked. It is one long cable that goes across the room, outside for a couple of metres and then across the IT suite directly into the switch (no patch panel connection). I have changed the port on the switch as well, just in case. (it is a new Procurve).
    The cable tester reports no issues but it still doesnt work.
    The cable has been in place for a couple of years and has been fine up until now, so it isnt a distance issue.

    My question is this - if the cable buzzes out as OK, what other issue could be doing this? Could moisture or something be a problem?
    I don't want to go to the expense of replacing the whole thing only to find that the issue persists!
    Sometimes it sucks to be a lone tech. No-one to discuss things with, and no-one else to share the blame!!

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    webman's Avatar
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    Try another computer on that port, or that computer on another port.

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    Do you get a connection light on the switch?

    What tester did you use? Did all 8 lights come on?

    I know what you mean, I have Manager jobs to do and Techy jobs!!!

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    witch's Avatar
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    Sorry, didnt explain very well. Have tried the teacher's computer elsewhere around the school and it works fine. Have tried other computers which work elsewhere around the school on that port - no go. No connection light on the switch that I can see. I also used a brand new cable between the port and the tester - in fact I tried several cables.
    I used my trusty cable tester and it hasnt failed me yet - all lights came on in the correct order.

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    Well it sounds more like your switch. Have you tried plugging the socket that is not working into a different port?

    Also one thing to try, is when you are testing the plug that goes into the switch to the socket is to wriggle the wire on the plug end at the switch. I had that where it worked when I had it out but failed when I put it back in because of the angle the cable was at.

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    plexer's Avatar
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    Your basic tester only checks that there in connectivity from one end of the cable to the other so even though it shows as ok there could still be issues with the cable.

    Ben

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    witch's Avatar
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    Have changed switch port

    Just worried about the cost and upheaval to change the cable if it isnt the problem

    * Have now stood and wiggled the cable at the switch end whilst someone else checks on the connection to the machine - no sign of a flicker
    Last edited by witch; 16th September 2010 at 02:14 PM.

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    SYNACK's Avatar
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    Quote Originally Posted by plexer View Post
    Your basic tester only checks that there in connectivity from one end of the cable to the other so even though it shows as ok there could still be issues with the cable.

    Ben
    +1

    The basic cable testers only test conductivity not for things like sque and jitter, I suggest asking around the local area to se if anyone has a good quality Fluke cable tester that you can try on it which can test for stuff like this. One of the High Schools or the LA network team may have one that you could borrow. I used to borrow them from my old University for a while. I have also heard that some places do offer them for hire, none here but the UK is much more tech friendly.

    Running a good quality tester over it should give you a solid answer so that you can do whatever is required with realitive confidence.

    It does concern me to hear that it goes outside for a couple of meters as I'd gamble that it is not outdoor cable and had probably become a bit corroded leading to higher resistance or signal jitter.

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    plexer's Avatar
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    Equipment Specifications - Testerhire.co.uk - providing hire of the Fluke DTX1800 cable analyzer hire fluke testing equipment but otherwise may be able to get a company to come in and test it if they will get the job of replacing it should it turn out to be faulty.

    Ben

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    witch's Avatar
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    Quote Originally Posted by plexer View Post
    Equipment Specifications - Testerhire.co.uk - providing hire of the Fluke DTX1800 cable analyzer hire fluke testing equipment but otherwise may be able to get a company to come in and test it if they will get the job of replacing it should it turn out to be faulty.

    Ben
    lovely idea but no one is going to spring that sort of money to test one cable. I will ask the high school if they have a better one than I have got to see if I can find a problem.
    If not I will contact a local company

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    Quote Originally Posted by witch View Post
    outside for a couple of metres
    If it isn't outdoor rated cable, it is likely to be moisture ingress through the jacket or general degradation of the copper. Any cabling that goes outside either needs to be outdoor rated, or encased in something. I have had exactly the same experience at a rural school here in NZ, continuity tested OK with the cable tester, but no go for connectivity. Unfortunately, the only fix was to replace the cable......

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    Quote Originally Posted by witch View Post
    lovely idea but no one is going to spring that sort of money to test one cable. I will ask the high school if they have a better one than I have got to see if I can find a problem.
    If not I will contact a local company
    I agree seems allot for one cable. You can get a brand new one fitted cheaper.

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    Quote Originally Posted by FN-GM View Post
    I agree seems allot for one cable. You can get a brand new one fitted cheaper.
    Thats why you turn it into a survey project when you get a hold of one or at least thats what I did. The enhanced testers will give you the length etc and the high end ones even store the tests in a downloadable format. I did a full survey of all the ports in the school and found/pre-emptivly fixed some that were likely to fail. It also means that I have a table of the run lengths and cable types of each cable run in the school which can be really useful if you need a quick answer about how capible a certain part of the network is.

    I would try to go for the borrowing route as that does look rather expencive an if you do end up replacing the cable then make certain it is done wih outdoor grade cable (about double the cost but it will keep working).

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    witch's Avatar
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    Have contacted a couple of local NMs and no one has a tester that is any better than mine. I have eyeballed the wire and it is encased in a black plastic sleeve. It was only put in a couple of years ago and we have others that have been there for many more years and not caused any trouble
    I'm going to have to have to bite the bullet, I think , and go for a replacement.
    May the GeekDeity help me

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    Cable problems

    Quote Originally Posted by witch View Post
    Have contacted a couple of local NMs and no one has a tester that is any better than mine. I have eyeballed the wire and it is encased in a black plastic sleeve. It was only put in a couple of years ago and we have others that have been there for many more years and not caused any trouble
    I'm going to have to have to bite the bullet, I think , and go for a replacement.
    May the GeekDeity help me
    Silly thought ... is it worth disconecting the cable from the classroom socket and putting a standard rj45 plug on it to see if that makes a difference ?? That would eliminate the socket having some kind of silly problem ..
    I'm over your way next week if you want a hand or 2nd opinion
    Cheers
    Brian
    Courthill School



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