Hi, I happened to run through your post regarding your yamaha electone organ piano button sound problem. Usually, when you press the upper keyboard voice (e.g. piano), it will produce piano sound on the upper keyboard. Similarly, with the lower keyboard. I think you need to get a technician to get it check.
Btw, what's the model of your electone organ?
Unless your organ is very old model, then it's no point getting repaired. If yours is the FS or EL series then consider getting it fixed. You can leave your hp contact & I'll pass you further info. Cheers!