My 414 had been giving me trouble for a couple of years. About 10% of the time the signal comes through weak or distorted. Sometimes the balanced signal wouldn't work at all unless I pulled the plug out a little ways. It usually happens just when I go on stage. Pulling and re-inserting the plug usually doesn't help. Sometimes popping out the battery box made it work? It was driving me nuts and I was about ready to have the entire battery/jack housing replaced with a new one.
It was getting scratchy when I wiggled the plug, any plug, so I knew it was not the cable, or the pre-amp. Before taking it in I decided in desperation to try one more thing. I plugged in and pulled out the cable 100 times in rapid succession. My arm was tired, but it worked!! It has not failed me since. It was apparently only dirty. Now I wonder how one best cleans the inside of the jack.