...more on the last post.... the techs, when they opened the technics keyboard up, found that by just applying some pressure to the board that it was fixed temporarily. not sure how or why but it didnt last long. So, the problem is definately in the circuitry.
I just would like to share some experience I had with a kn6500 I bought for parts a few years ago. The guy told me that the keyboard behave strangely with some weird sounds coming out of it and when he sent it for repair it came back even worst than before.
So I bought it anyway for a few dollars thinking I could maybe repair it. I'm no electronic technician but I used to be a senior cash register tech and like to fool around with broken mechanic or electronic things.
I removed the back plate of the kn and turned it on using a piece of wood wich is not conducting electricity and start touchings the board inside until I realized that putting pressure at a particular place inside the problem woud dissapear.
Looking closer, it was a big chip with lots of pins and I tought that maybe there could be a bad soldering there. So I brought the keyboard to my technician telling him my discovery. And guess what?
That was the problem and he resoldered the pins and that fixed it.
I think your motherboard may only have the same kind of trouble I had. Ask your technician to dig in.
Cheers and good luck !