Hi,
I believe that there should be a -12 volt buss if the KN3500 follows the typical design of the Technics products. I also had power supply problems with my Technics SX-xxx spinet organ and it had the same power supply setup.
Be sure that the power busses are powered up even though the power supplies are working. I seem to remember that some of the fuse resistors were in the output leads to the busses. When I find my KN2000 schematic, I can check better for you.
Walt