SXPX73M No Sound From Internal Speakers

I have a SXPX73M that has a sound failure from the internal speakers. At turn-on I get a couple of seconds of hiss and crackle and then nothing. A factory reset does nothing. I get normal sound and play through the headphones. I have connected the headphone output to external stereo speakers which gives me sound but with a limited volume. The audio jacks on the back are no help. My electronics guy thinks there may be a short somewhere in the piano speakers. He is hesitant to blindly dig into the machine a possibly cause more damage. I would appreciate any advice that would help restore the internal speakers. Thank you.