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5V MUST appear in the first few seconds w/ or w/o LCD connected.
But will disappear fast if LCD is not connected.
Once LCD is correctly recognized by PCH, voltage is maintained.
Keep LCD connected, when diagnose image, or backlight problems.
Check if DP_INT_HPD goes high at same time with 5V on L8300.
If yes, post PPVOUT_S0_LCDBKLT voltage.