My guess is if these 2 lines are in order, like 1-2 or 3-4 or 5-6 and so on, and you say your backboard is a mess? The Installer may have crimped his modular ends (the plugs with 4 brass pins that go into the CO ports on the system). Hand crimped Mods have a high failure rate. If the problem is indeed on say for instance line 7-8 then swap the plug with 5-6 and if problem follows, before calling the telco, and if you think you are capable, put the two lines on a jack and use a NEW Station CORD, with 4 brass conductors, that may solve. I recommend trying the other troubleshooting procedures mentioned earlier as well. Good Luck.