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Tracking down a "miswire"

Posted on 2006-06-05
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Last Modified: 2010-04-26
ok, this one has me stumped.
cat 5e cable runs from server room to an office through the ceiling.  in the office, the cable is terminated using B-standard.  i have wired this termination at least 4 times now, so i'm 100% positive the wiring is correct.

at the server room end, the cable goes to a patch panel.  i have wired the port on the patch panel 3 times now, and i am 100% positive i have it wired correctly.

i connect a patch cable to the patch panel, and connect one end of a cable tester.  in the office, i use another patch cable and connect the other end of the cable tester.  the cable tester flashes miswire on 1-2, 3-6.

i have tested both patch cables independently, and they are not miswired.
i have taken the terminator off the end of the cable in the office and created a circuit by stripping the covers off the wires and twisting each pair together.  i then go to the server room and test for continuity.  the continuity PASSES.  to verify, i untwisted one pair in the office, and continuity fails (as expected).

so, the cable itself is ok.
i replaced the terminator on the end of the cable in the office with another terminator to verify it is not bad.  the problem still exists after swapping out the terminator.

the only thing left in the path is the actual patch panel port itself.  i am now wondering if there could be something wrong with it.  i did all of my troubleshooting on port 1, but port 2 is also giving the same error.  there are 12 other cables that are running through the ceiling and have the same wiring at the patch panel and at the terminators, and these runs are working fine.  tomorrow i am going to try to rewire the cable at port 1 to another port on the patch panel.  i still have another 10 or so open spaces on the patch panel, so i will try moving the cable going to port 1 over to the next free spot.

is there anything else i could be missing here?
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Question by:zephyr_hex (Megan)
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by:Irwin Santos
Irwin Santos earned 400 total points
ID: 16839827
if the patch panel allows for another brand new jack....(empty hole).. add a spankin' brand new one.
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Gary Case earned 1600 total points
ID: 16840042
When you tested for continuity for each pair (with the ends twisted together in the office) did you also test for continuity with ANOTHER pair?   The cable may have an internal short -- in which case you would "see" the continuity you expect ==> but would also have continuity across pairs.   To test this, you need to check each pair against ALL OTHER pairs when you're doing the continuity test.   And this still doesn't check for an internal cable short between the two wires of a pair => to eliminate the possibility you should check EACH wire for continuity with all 7 other wires with NO shorts at the other end (there obviously shouldn't be ANY continuity in this case).  I'd do this last test AFTER re-terminating the cable in the office => that way it will also confirm there are no shorts in the terminator.


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by:zephyr_hex (Megan)
ID: 16843406
how do i check each pair against all other pairs for continuity?  (twist a pair together to create a circuit and then ???)

and to check continuity of each wire...  terminate the end in the office, and then check continuity on each individual wire with no twists/circuits?

thanks
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by:Gary Case
ID: 16843470
With the end terminated in the office and NO connections ...

... go to the other end;  attach a multimeter to one wire, say #1, and then touch the other probe to #2, #3, #4, #5, #6, #7, and #8 in succession.   There should be NO continuity with any of them => if there is, you have a short in the cable.   Now touch the probe to #2; and test with #3, #4, #5, ..., #8;  then touch the probe to #3; and test with #4, #5, ..., #8;  etc.   This will comprehensively confirm you have no shorts in the cable.   This -- PLUS the continuity test you already did -- will together show that (a)  no wire is broken internally (otherwise when you shorted the pairs you wouldn't have had continuity); and (b) there are no internal shorts in the cable (which your earlier test did not check for).
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by:zephyr_hex (Megan)
ID: 16843540
ok.  thanks.  i will do this later today and post results.
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by:Caseybea
ID: 16845278
This sounds like a cable that got spliced together up above the ceiling somewhere.....................................   (and spliced wrong).     My guess.
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by:Gary Case
ID: 16845433
"... i'm 100% positive the wiring is correct ..." ==>  From your description of what you've done; and your troubleshooting efforts to this point, I'm certain you're right.   You've done all the right troubleshooting steps; and once you confirm there are no shorts you'll know for sure if the cable has any issues.

But whenever I see this kind of statement I'm reminded of a couple years ago ...

Bought wife a new car;  she wanted a spoiler to "dress it up".   Dealer messed up and forgot to include it with the order -- no problem; he'd send someone out to install one...

Guy came out;  dutifully installed spoiler, and was ready to leave.   I asked him to turn on car and step on brakes so I could see the lights on the spoiler.  He was a bit miffed -- "sir, I've installed hundreds of these - there's no doubt it works."

To humor me he turns on car and steps on brakes -- brake lights turn on, but no spoiler light :-)

I suggest he check his wiring;  he's further miffed and says "wiring's okay, it's got to be a bad light in the spoiler."   Replaces light in spoiler.  Still no light.  STILL convinced his wiring's fine, he went to lunch; stopped by the dealer; got a new spoiler; and came back and replaced the original.   Still no light.

Finally he checked his wiring to the taillights -- as you can tell my now it was wrong :-)

... very embarrassed young installer fixed his problem and left ...

I wonder if he checks his work a bit better these days ...
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by:Gary Case
ID: 16845446
... type alert:  obviously in the 3rd line from the end "... tell my now ..." should be "... tell by now ..."
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by:Gary Case
ID: 16845464
Arrggghhh !!   Misspelled "typo" in my "typo alert" !!!!

... this site needs a Preview button !!  (Spellcheck would be nice too)

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by:Irwin Santos
ID: 16846680
"Arrggghhh !!   Misspelled "typo" in my "typo alert" !!!!"
getting old... ;-)

If the above doesn't work.. .I normally cut off 3-6' off the ends (if you have that much slack).  And if THAT doesn't work... Re-do the entire run.  Nothing more frustrating than fixing someone else's stuff.
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by:zephyr_hex (Megan)
ID: 16847528
cable passed the continuity checks suggested by garycase (no continuity indicator when testing individual wires).

caseybea - i know splicing isn't the issue.  i ran the cables myself, and all of the cable continuity checks were pointing to a good cable.

sooooo...
i went ahead and wired to a new port on the patch panel.  wha-la.  for whatever reason, ports 1 & 2 are bad on this patch panel.  this explains why the two runs were having identical errors when punched down into the panel, yet the cables were showing no errors when not punched down to the panel.

i was going to re-run the cables if changing the port on the patch panel didn't work... as a last resort.  luckily i found the problem before rerunning the cable.  it was also a relief to see that i wasn't going crazy and that i had wired everything right.

thanks for the assistance.  learned some new troubleshooting techniques.
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by:Irwin Santos
ID: 16847575
cool..thank you!
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by:Gary Case
ID: 16848650
Glad it's resolved.   Once you confirmed the cable was good -- and if it passes both the continuity check with pairs shorted and the "lack of continuity" check for each wire against all others it will ALWAYS be good -- the problem HAD to be either a bad termination (heaven forbid -- and I AM convinced you had done a thorough job of eliminating that possibility before you even posted the question) OR a bad patch panel.   Fortunately it's only a couple of ports on the patch panel :-)
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