Mark, my headphones have broken, but only after years of using them. Have you tried to using the same headphones with a different keyboard?
A little off the topic, but maybe not. I no longer use headphones – I now use a headphone. My right ear is now deaf. Sad, yeah but my left hear is working very well, good enough to sing on tune, hear my wife’s voice and tune a great piano.
Life is good, John C.