The error D900 means that there is something wrong with the printed circuit board. First, you can perform a reset of the printer to clear out anything that might be on the control panel.
To reset this machine:
1– Make the numeric keypad visible on screen by pressing the Fax button.
2– Locate the Asterisk (Star) button on the numeric keypad.
(Remember step 1, 2 to display it)
3– Display the main menu by pressing the Home button.
4– Open the front cover of the printer to access cartridges.
5– Press and Hold the Asterisk (Star) button for 5 Seconds during step 4.
6– Check the reset menu on the LCD display.
7– Scroll through the menu to select a color and yield to reset.
8– The LCD will read “Accepted” once the reset is complete.
There are only 3 remedies for this if a reset doesn't work.
1.) You check the panel PCB harness connection and reconnect it.
2.) You replace the panel cover assembly.
3.) You place the main PCB assembly.
I would recommend getting the printer serviced if it comes to that.
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