User's Manual

Chapter 18 Maintenance and Troubleshooting
Resolving problems
SmartClass TPS User’s Guide
158 22035456, Rev 001 May 2014
To measure DC volts, remove the line battery and measure Tip (A) and Ring (B) to Ground (E). It
should be < 3.0 volts; anything else indicates crossed battery that inhibits digital signals.
To check for span/battery voltage, measure Tip (A) to Ring (B) across several pairs. On good lines
Tip (A) to Ring (B) will be 48–52 volts, Tip (A) to Ground (E) will be < 5 volts, and Ring (B) to Ground
(E) will be -48–52 volts.
Issue
In the winter, the DC current measured 21 mA from an aerial cable at the NID with are no problems.
In the summer, the same line measured 17 mA.
Resolution
The heat has increased resistance and lowered the current.
DC current on Tip (A) to Ring (B) should be  23 mA at the NID. Anything less will not allow for differ-
ences in temperature and phone equipment will not operate during extremes.
The 23 mA threshold covers most temperature extremes.
Issue
The resistance measurement on Tip (A) to Ring (B) is 3.5 M, Ring (B) to Ground (E) is 3.5 M,
and Tip (A) to Ground (E) is 5 k.
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 116.)
Issue
Two loops in the same bundle display different loop lengths.