Chapter 18 Maintenance and Troubleshooting
Resolving problems
SmartClass TPS User’s Guide
156 22035456, Rev 001 June 2014
Resolution
There is a ground fault on Tip (A). The typical resistance is > 3.5 M. Lower values indicate a short
or ground fault
Loop resistance is measured with the pair short circuited (shorted) at one end, so a much lower
resistance value is measured, as the current can readily flow down one lead and easily back up the
other across the short. This “loop resistance” measurement is often required to qualify HICAP (high-
capacity) circuits such as ADSL with values approximating 700 .
Resistance is measured not only across Tip (A) to Ring (B), but also from Tip (A) to Ground (E) or
Ring (B) to Ground (E). Resistance is also measured from one lead to Ground (E) to check for
shorts to the shield and other ground references, indicating a fault on one lead of the wire pair.
Resistance measurements made to Ground (E) are used to compare the resistance value of one
lead to the other, to see how much difference exists in the resistance of one lead compared to the
other. It is important for both leads to be nearly the same (resistive balance), and a difference of
more than 3 percent is usually considered unacceptable.
Issue
While running the Opens test, the mutual value looks good, but the Tip (A) and Ring (B) values are
really short.
Resolution
Verify the ground. The module must be grounded to the same ground as the pair under test. (Use
the Current test to verify the ground. See step 10 on page 114.)
Issue
Two loops in the same bundle display different loop lengths.
Resolution
Use a known good loop to determine capacitance, then run the opens again to determine the length
of the bridge tap or location of the fault. Verify with a tester that has TDR capability.
Measure multiple vacant pairs by attaching one lead to Ground (E) and using the other to the Tip
(A) of each vacant conductor. (Battery should be removed) Compare the distance for each for
consistency.
Opens/Capacitance: < 3% difference between Tip (A) and Ring (B) values indicate an acceptably
balanced loop. Anything greater indicates an unbalanced line or open fault, which inhibit digital
signals.
You can also compare the distance from the Opens measurement to a resistive distance measure-
ment, and determine the presence of a bridged tap by the difference in the distances.
Issue
The balance measurement is 50 dB.
Resolution
The pair quality is too low as it should mitigate 60 dB. The balance result should be >60 dB.
Anything less indicates electrical differences between Tip (A) and Ring (B) that can lead to noise
and other signal problems.
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