Hello, my name is Rusty. I want you to test the headphone jack. That is what is able to short out. Play it through the headphone jack for a while, see if it shorts out. If it does not, your headphone jack will need cleaned or replaced.
To clean it, unplug the piano. Dip the headphone jack into rubbing alcohol, and run it in and out of the jack several times.
If the problem persists, it is most likely the headphone jack. There are two amplifiers for the speakers, so if one is shorted, the other should still play. The headphone audio will tell us a lot about what is going on inside the circuitry.