If it is the board, the board itself only cost about $20 from Yamaha, but first you need to determine if this indeed the problem source. This would require taking the keyboard apart and checking the headphone jack's PC board.

Gary cool
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!

K+E=W (Knowledge Plus Experience = Wisdom.)