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T1/DS1 Troubleshooting

A few days ago I had to extend 4 circuits over a distance of about 600 feet using house pairs in a high-rise building. I then tested all 4 extensions for wiremap and other faults (including split pairs) and all

4 passed. After patching the extensions into the appropriate smart jacks, I had the LEC test the circuits while I used a loopback plug. Three of the circuits tested fine, but on one circuit, they could not see the loop. I then plugged the loopback plug directly into the smart jack, and they could see the loop.

After serverl hours of waiting on hold, switching house pairs, switching patch cords, etc... with no success, we tested the same circuit with a different extension (that had previously worked fine on another circuit), and it still failed. We are now waiting for the LEC to come out and do some additional testing on the circuit.

My question is... without these additional extensions, house pairs, and other circuits available for troubleshooting, how could I have ruled out the extension as the cause of the problem?

Reply to
Michael Quinlan
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Michael Quinlan wrote in part:

Not easily. Substituting "Known good" into a failing circuit is a time-tested diagnostic method. Subsituting "suspected bad" into a working circuit is even more powerful.

One thing I'd do: put a DVOM across the unpowered loops with a loopback in place and check resistance. It should match the wiretable. If it's off, ground each leg and test for balance. You can also leave'em open and check for ground leakage.

-- Robert

Reply to
Robert Redelmeier

Yet, after coming to the conclusion that the cabling was not the cause of the problem, it took the people at the office 2-1/2 hours to convince the LEC of this and release me from the site.

Wiretable?

Another thought that crossed my mind with regard to this is that with a

600' extension, the actual tested cable length while using a loopback plug is 1200'. So, is the fact that the circuit failed with a loopback plug necessarily an indication that it would not work once the CPE is installed?
Reply to
Michael Quinlan

Michael Quinlan wrote in part:

Unfortunate. The stubbornness of LECs might reduce their costs, but it increases everyone elses's.

Sure! I've got a nice wiretable that shows copper resistance:

24awg = 25.67ohm/kft (@20'C).

Any time-of-flight tester had better take the loopback into account!

No necessary correlation. If it's a dead-short loopback, it could be drawing more power than the CPE.

-- Robert

Reply to
Robert Redelmeier

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