LCD only works when charging, remains black afterwards.

Ok, so I have extensive repair experience but I cannot figure this one out. It is not a backlight chip or fuse resistor. The LCD functions perfectly when the battery is dead and charging. Shows that it is charging and lights up when buttons are clicked. Once the phone passes 5% and begins to power on the apple logo blinks for a fraction of a second and then the screen stays black. The phone completely powers on and the touch even works just the LCD remains black. I have even transplanted the logic board in a completely different frame so the problem is on the motherboard. Any ideas?