I just repaired the same problem on my P-120. Turns out the problem was a broken trace on the pc board the jack was connected to. I had to desolder the connection and replace the trace with a piece of wire. That solved the problem. Also, the connector on the P-120 is not a typical yamaha connector. Most yamaha boards are 12vdc and the P-120 is 16vdc. the adapter is larger and more complicated and the connector is larger than a typical yamaha connector. Be very careful, because that trace is extremely close to another that must remain separated. It would be way too easy to create a solder bridge that would be in error.