REQ Tektronix phaser 550 repair manual

So did you find the problem? If you are still getting the error that the door is open, it is probably just a small $2 microswitch that needs to be replaced. Try opening and closing the front door really fast. You will normally hear a clicking sound from the small microswitch buried in the back of the printer under the main board. If you listen very carefully you will hear the clicking sound coming from the back of the printer. Ideally the engineers could have made the switch more accessible because with the current going through it (the switch) it is not uncommon for the contacts switch to pit and/or oxidize over time. Replace the switch and the error should go away.