I sheared off a plug from a 3.5 mm headphone jack inside my Roland HP603 piano. After failing to remove the plug, I tried removing the 3.5 mm jack socket from the PCB.
However, the piano still thinks that headphones are plugged in. I think that I need to connect certain pins on the board to fool the piano into realizing the headphones aren't plugged in, but I can't find any circuit diagrams. The jack I removed has 9 pins (not sure why so many, maybe related to 3D sound).
I think part number for that jack is PJ30150. If I'm looking at the datasheet correctly, connecting pin 4 to pin 5 and pin 6 to pin 7 should do the job.
It is hard to tell from the photo, but you may be able to fix this properly.
My best guess: the missing socket could well be the 9-pin 3.5 mm Jalco YKB21-5344N that Roland often uses. You should check if I identified it correctly. A photo of the missing socket would help, by the way.
You could buy a new one (several suppliers have them) and try to solder it in, or look below for the connection of the switches in the jack socket to make the patch you propose.
Source: Roland FP-10 manual
With no plug inserted this socket connects pin 4 to pin 5, and pin 7 to pin 8. You can easily check this with a multimeter if the jack socket you removed is still more or less intact.
