@stefvandermeer you should be able to tell by looking at the display from the side whether the backlight is working. You could also use a multimeter to see if there is any output from the backlight inverter. The part number for the inverter chip is at https://docs.duet3d.com/en/User_manual/Troubleshooting/Parts#paneldue-tft-panel-backlight-inverter-ic.
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