The K5000s is a nightmare inside. However, I fixed one once just by re-seating a loose circuit / card that was deep inside (still a nightmare). Least favorite synth I've ever owned. Good luck. Be careful if you open it up.
While the K5000S doesn't have a hinged top panel for easy access (like some eighties synths), I found it easier to take apart than many other nineties synths i've looked at. I remember taking the bottom off my Wavestation when it broke and thinking "No way!" and then putting it straight back on. There are quite a few screws to undo on the Kawai, but, with a little patience, it doesn't take too long.