Thanks Han for the photo. I encountered the same message (“No cassette”) after replacing the belts of my DCC380. I did not properly put the black cables back to their place. This interfered with the switch CASS_IN on the bottom of the photo. Putting the cable in the right spot solved it. I would not have figured this out without your photo.
Thank you for this explanation! 
I had the same problem after replacing the gear wheel. But after re-adjusting the pcb with switches the message “no cassette was gone”.
Hello,
During my last DCC 600 revision… Gear, both Belts and pinch Rollers replacement appears that message after all the hard procedure to dismount and reassemble of deck module!
The reason was the board where is the most difficult connector location that, when forced to clipped, as moved from its fixation and terminal “relays” of cassete detection don’t actuated correctly sending the message… “No cassette” .
