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"U7700/17 0V"
Missing enable signal for backlight.
"PP5VR3V3_SW_LCD got 5V
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U8330/3 0V"
This is not possible, unless U8300 is shorted.
EDP_PANEL_PWR_OR_PSR_EN is required to enable 5V on pins 28-30 of J8300!!!
If you checked these voltages without LCD connected, NOT good.
Check all again; less keyboard backlight signals/voltages (not needed).