(1) Open and close the front door, then try again.
(2) Power printer off, unplug the main power cable, use knob wrench to remove the back cover of printer. Locate and re-plug plug-J38 in lower right corner of main board. Then, power printer and and start a printing test.
(3) Replace front door interlock sensor. (Step of replacement)
(4) Check the cable from interlock sensor to mainboard. Replace the cable as needed.
(5) Replace the main board. (Step of replacement)