1. Connect the Duet via USB to a PC running a host program such as Pronterface. Send M111 S1 P3 to the printer. This will echo to USB all gcode commands received. If you see messages that start "aux":, those are from PanelDue. In which case, the PanelDue is probably working correctly but the backlight inverter on the TFT panel may have failed.
2. Connect the PanelDue via USB cable to a PC. If Device manager shows "Bossa program port" under "Ports (Com and LPT) then you have probably pressed the Erase button on PanelDue and you need to re-flash the firmware. OR you can presse Erase followed by Reset anyway, check that the Bossa Port appears, and re-flash the firmware anyway.
Please note, many USB ports provide insufficient power to power a PanelDue with a 7" panel attached.
Thanks for your rely David,
So I've tried what you told.
1. I connected the duet to PC and send M111 S1 P3 to the printer and here is what it replies:
Debugging enabled for modules: GCodes(3)
Debugging disabled for modules: Platform(0) Network(1) Webserver(2) Move(4) Heat(5) DDA(6) Roland(7) PrintMonitor(8) Storage(9)
So, no messages start "aux".
2. I also tried to connect paneldue via USB to a PC and a mac but my device manager doesn't seem to know that it is even connected. I am sure that the USB port works since I also used it to connect to the duet.
I guess that it is the board that fails? But I am not understanding why. Maybe I should just replace the board?