What kind of DEC did you replaced? Did you use Galileo Dec or Avantra? How about the removable Ics ? Did you replace them? Could be the possible broken pins.
If you used the correct and reliable Galileo DEC, then the second consideration might be the cables connected to DEC and the carriage. Have you worked on the carriage and the flat cable connector? The flat cable must be connected to the right 4c pcb's slot.
I need to know how the red LED reacts to the power on sequence.