Need help with crackle, pop, spit sounds from Roland KR-370

Tried to have it serviced in Phoenix area, but no one will touch it.
Everything was fine until we left the piano in a very warm house (88-90 degrees) for five months this summer. It pops, crackles, and spits both through the headphones and speakers.
My MIL bought it in 1998 for $2899 in Seattle. Don’t want to trash it for sentimental and monetary reasons. (I sold my old Roland 1000 for $100 when we rcvd this from her estate.)
Could anyone give me an idea of what replacement parts to try? I know nothing, but am willing to try anything.