i purchased a KN6000 that did not function except for a piano sound. It had no led’s and no button function. If I would power it on while holding a few keys the Home Screen would come on,but a normal power up would just give me a Error in CPU data transmission. After downloading the service manual I started doing voltage checks on the FAJ board. I found that the 5.0 volts was missing on device IP 1. It is a IC protector rated at 400 milli amp. It was very inexpensive and easy to change. It cured the problem. Everything functions as it should.