My miracle piano is starting to go bad. The left speaker plays no sound (and neither does the left channel of the headphone jack), unless power is turned on and off rapidly. One piano key needs to be pressed hard to get it to respond. Any ideas?
Probably a bad connection in the audio path. Sometimes a bad connection can conduct when more volume is pumped through it. The old Mac IIsi suffered from this problem, also a garage sale stereo in the speaker switch. It might even be the headphone jack; I had an all-in-one stereo where the damn headphone jack was the culprit of lousy audio. I had to pull the thing apart just to bypass it. I imagine you could find the bad connection just by opening it and jiggling various parts until the problem responds to this.