Cat5 point not working but testing ok

KAGY

Hi all,
I installed CAT5e in the house when it was being built and I was trying to use a point that I haven't tried before to install an RPi htpc in the play room. No joy.

I've a simple two part cable tester that flashes 1 through 8 to test the connection (end of cable i'll be using back to switch) and it flashed 1 through 8 in sequence with no shorts. But the RPi (and my laptop) aren't connecting through. I've tried a different known working cable in the same point, still nada. I'm plugging straight into the eircom d1000 router because I'm only using 4 points (so no use powering up the 16 port switch I have) and I've no trouble with those.

What should I try next? It's obviously the cable running through the house (about 10-12m max at a guess) but that's testing "OK".

runawaybishop

Are you using A or B? Do the rest of your ports work fine?

KAGY

Bledin' 'ek that was a quick reply:) I was just coming back to edit, I'm using T568B

runawaybishop

Those testers just check that there is a connection between the wires, they don't check if they are in the right order. First thing i would check is that you are wired correctly and using the same as the cables you are plugging in.

KAGY

These testers: I thought that if pin 1 was connected to pin 1 etc then it was wired correctly for a straight through cable.
I'll do a visual on it and redo the plug and cable end

runawaybishop

KAGY wrote: »

These testers: I thought that if pin 1 was connected to pin 1 etc then it was wired correctly for a straight through cable.
I'll do a visual on it and redo the plug and cable end

I think they just test both automatically from the little time i spent checking them out on ebay - kinda hard to tell.

It shouldn't matter if your entire house is wired in A and you did that run (not port) in B, but it will matter if you wired it incorrectly and made a crossover cable and its a pretty easy check to make visually.

KAGY

redid both sides, again testing ok with that tester, but still "Network cable unplugged" I'll get out the multimeter later and test it that way, but for now beer and patio are beckoning :pac:

edanto

At either end of the troublesome cable, are the twisted pairs unwound for any significant distance? More than an inch or two? It would be rare to see it at such as short distance (10m), but unwound pairs can cause a cable to fail.

Similarily sharp bends in the cable (the little microtwists that sometimes appear as you are running the cable) can also cause it to fail.

Finally, if the cat5 cable is adjacent (close than a foot) to a power cable for any significant distance, that could cause interference. You always want cat5 crossing power perpendicular IF it has to cross.

Perhaps one of the punched down connections is a little flaky and good enough to pass the simple test, but too flaky for a network connection. If the other things above aren't an issue, reterminate.

After beers in the sun!

KAGY

Okay, thanks for your help, I eventually figured it out. Down to something as simple as mislabelled wires. I thought that if the connection was "flaky" as edanto puts it, maybe the dynamode switch would have more power. Plugged it all up and hey presto, port 8 lights up instead of port 12. Now just to figure out why it was testing ok, AFAIK the tester more or less applies a voltage across pairs of wires and the remote section is powered by this so shouldn't light up. Unless the labelling is completely messed up and the switch was connecting the ports together? Can't remember now, but if I had the active part at the far end that might make sense.

Moral of the story, don't trust €5 chinese testers. Or is it " a beer in the sun solves all network problems!"

edanto

Great, glad it's sorted.

Best not to involve a switch in any cable testing, not sure why you gor that confusing result, but hey all good now.