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I have a CAT5 jack that was working fine and seemingly stopped transmitting data all of a sudden. I use this for my TV's internet connection.

My setup is pretty basic and straight forward. I have a central smart box where this run connects to an 8 port switch which connects to the router.

Troubleshooting steps I've taken:

  • I've tested the run from the central box to the port using a signal generator. All pairs show all signals received.
  • I've checked the ethernet cable from the port to the TV with the generator and it's also good.
  • For good measure, I've even replaced it with a known good cable.
  • I've connected my laptop to the same port on the switch to verify internet connection there, and I connect to the internet (ensured laptop wifi was turned off) and no issues there.
  • I also connected my laptop to the wall port used for the TV and the LAN's LED adapter doesn't indicate it's connected and neither does the laptop's internet protocols interface.

So if all connections show good, but nothing will transmit, what's going on?

With hopes I've explained my situation clearly and understandably, can anyone tell me why I can't get an internet connection? Thank you in advance for your help.

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    so you checked continuity of each wire but did you check for shorts between wires? Anyone drive any nails into a wall?
    – DoxyLover
    Mar 30, 2022 at 4:27
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    possible rodent damage. Mar 30, 2022 at 4:52
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    Can you temporarily move the TV to the same place as the switch, for testing? Or can you borrow/buy a long-enough ethernet cable to prove the length in the wall is the faulty piece?
    – Criggie
    Mar 30, 2022 at 9:44
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    You appear to be passing into the zone where things for general electronics ("signal generator") need to be swapped out for things specifically meant for UTP ethernet. Or just re-terminate the cable ends, and if that does not work, replace the cable.
    – Ecnerwal
    Mar 30, 2022 at 15:12
  • Has the TV had a recent firmware update? Or have you experienced a recent electrical storm in your area? It sounds like the TV is at fault here.
    – TylerH
    May 5, 2022 at 14:02

2 Answers 2

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If you want to keep pecking away with the wrong tools, chop a patch cable in half, strip the wires, and plug it in (with the other end of the cable unplugged) and verify no connection from any wire to any other wire.

Then strip the wires on the other half, and twist each pair together, plug it into the jack at the far end and verify continuity of each pair from the other end.

That's the sort of thing you can automate/do more easily with a $10 ethernet tester; or laboriously with a cut patch cable and a multimeter.

After that your twisted-pair ethernet wiring tester options move to "hundreds or thousands of dollars" and replacing the cable is cheaper.

If both ends of the cable are connected to jacks (as is proper) start by pulling them out and re-punching the connections into the jack (for which you need a punchdown tool, barring weird tool-less jacks.) If the other end is a crimped-on plug, that's instantly your suspect (and you have a harder time checking continuity) as plugs crimped on wall cables fail with some regularity. Replace it with a jack and a patch cable. You can try replacing the jacks, but unless you see an obvious issue by visual inspection, jack failures are relatively rare.

Edit: You state in a comment that "One end has to be crimped as it connects inside a low-voltage box similar to OnQ" - by using a surface-mount jack enclosure you can, and should, use a jack (and short patch cable) there as well. They come 1, 2, 4, 6 or more - I show a 2 below. The surface-mount box can be installed inside the "central smart box" - a good "central smart box" would have punchdown (like the jacks) patch panels available for this purpose, but a generic surface-mount will work. "OnQ" does seem to have 6 or 8-port punchdown patch panels available. I show an 8 below. They are rather expensive and space inefficient, as they leave the punchdown out and that takes up space. Little 12-port patch panels with the punchdowns on the back (you have to dismount them, install the cable, and remount them - which you do only once, or at most once per new set of cables) are available for generally considerably less cash, and take up less space in your box. The last item shown below.

Two-port surface mount from ShowMeCables

8-port OnQ patch unit from LeGrand

12 port patch from MonoPrice

So, at that point, you are likely better off replacing the cable, rather than spending a large amount of money for a tester you will use rarely or never that will most likely tell you you need to replace the cable.

One hack you can try (after having tried simple re-termination) which might get you from no connection to 100Mbit (better than nothing, and likely plenty for most TV uses) is to connect "the wrong colors" to your jacks. If you have no connection, the 1,2 & 3,6 wires (orange and green pairs in TIA568B scheme) have a problem. If you connect the blue and brown pairs (4,5 & 7,8)as if they were orange and green (so to pins 1,2 & 3,6) you might get a functional 100Mbit connection if the cable damage is confined to orange and green. The signals don't actually care what color the wires are, so long as they are paired with each other correctly.

If not "poor connections at the ends failing" the usual suspect is "rodent chewing cable damage" in a concealed location. While there can be other causes of cable damage, you state no construction activity, and that one is all too common.

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  • The signal generator I'm using is an actual tool designed for testing CAT5/6 and coax cabling. All pairs and connections show as properly paired and signal is good.
    – brehma
    Mar 30, 2022 at 16:48
  • So, probably the $10 pair tester level of tool?
    – Ecnerwal
    Mar 30, 2022 at 16:59
  • I really don't think so, it's been a reliable tester. I've had it for a couple years and I didn't get bottom of the barrel, bot that price really means that much, but it's more like a $30 Klein(?) tester. It's not in my hand atm so I can't remember the brand off the top of my head.
    – brehma
    Mar 30, 2022 at 19:06
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    So, something similar to the Klein VDV526-100, presumably. Whether you paid $10 or $30, it's not sending "signals" it is applying voltages at DC and detecting them. It's not doing TDR, skew analysis, etc. like a $350-$2K (or more) cable certifier unit. I own and use both kinds - nothing wrong with the cheap ones and they are all that a typical user needs or can reasonably justify spending the money for, but they have limitations when it comes to testing data cables. When you can work around the limitations you don't need more, when you have to document for others the fancy ones are needed.
    – Ecnerwal
    Mar 30, 2022 at 19:47
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    I'm utterly not suggesting you need a fancy expensive tester - you just need to understand that a low-end tester can be happy with a cable that a computer and switch won't like, and act appropriately (as answered above.) Also - if you have a plug crimped on your cable, try wiggling the connection and re-testing. But just replace it with a jack, that is the right way to avoid plug-on-wall-cable problems.
    – Ecnerwal
    Mar 30, 2022 at 19:49
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As I understand it, you have a problem with your TV.

You tried a new cable eliminating that, put a laptop on the cable, that worked so that eliminated the router port. Nothing left except the TV. I have a 96" Vizio TV that works great but the internet does not work with WiFi or cable. I followed the same route you did. I decided the best solution for me was to purchase a Roku. I connected to a HDMI port and it works great. It took several months for it to fail, starting to show more and more buffer underruns and eventually quit.

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    This. Electronics do fail. About 15 years ago, I purchased a snazzy new receiver with HDMI switching. Shortly after the warranty expired, so did all the HDMI switching. I contacted the retailer (a high-end AV shop in town) who told me that's not an uncommon situation (of course, they didn't mention this before they sold it to me...) and that the solution was a stand-alone HDMI switch or a new receiver. A cheap stand-alone HDMI switch has been working just fine ever since. Sadly, OP is now in the position of a new TV, no internet connection or a workaround such as the Roku.
    – FreeMan
    Mar 30, 2022 at 11:49
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    The OP tested the router port with a laptop at the router, not at the TV. The cable in the walls between the router and the TV is what's suspect.
    – brhans
    Mar 30, 2022 at 13:15
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    Read the question carefully. The Questioner also tried the laptop at the TV location, and it does not work there, though it does work plugged directly into the router port. So, bad cable run to the TV.
    – Ecnerwal
    Mar 30, 2022 at 15:02
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    "connected my laptop to the port for the TV". I think Gil & I both misread that as "I connected my laptop to the TV", not "I connected my laptop to the router where the TV normally plugs in". That misread does change things.
    – FreeMan
    Mar 30, 2022 at 15:28
  • To clarify, yes, I plugged my laptop at both locations, meaning at the switch to the router to verify the switch is working properly, and at the port, so substituting the laptop in place of the TV. The run in the wall shows good, no new construction work that would inadvertently pierce the cabling. The TV's port is not in question as the data doesn't reach the TV.
    – brehma
    Mar 30, 2022 at 16:05

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