if they have a molded plug(unscrewable)
cut one jackplug off
bear the wires back slightly, and with a pair of pin
nose pliers tug gently on the inner then outer wires
if any pull out the length of wire is how far up the
cable the break is (it could be intermittant)
if a break is found cut the cable back and refit
a good quality screened jack
do the same at the other end if necessary
if no "near end " breaks are found then check for continuity with a multimeter
most cable breaks of this type are nearly always
"near end" by the jack plug
al
July 2008