My machine still shows the same: call service

You will have to call a Copystar or Kyocera technician to reset your fuser memory.

A C6400 Error code can be caused by several different things:(1) A poor connection between connector YC-7 on Engine Printed wiring board and connector YC-2 on Power Supply PWB (2) Defective Power Supply PWB (3) Defective Engine PWB
Note: If you are not a trained Copier Technician you might want to let an expert handle this one. Because this will involve some dis-assembly of the machine and if you are not sure of how to remove the covers and check the electronics, you could cause further damage to the machine and possible injury to your self.