MacBook Pro A1990 No image repair

Problem description
When the MacBook does turn on but there is no image on the LCD. Backlight may be present but the screen is black

Symptoms

 * No image on LCD

Solution

 * Check the LCD cable and the connector on both the screen side and the logic board side.
 * The backlight power line is right next to the eDP data line for the image.
 * Any minor corrosion here results in 30 volts or more going to the displayport mux, U9850.
 * U9850 is what the dedicated GPU and the CPU's integrated GPU go to before it goes to the screen.
 * Unlike the 13" machine where the backlight voltage destroys the CPU, here it destroys a cheap chip.
 * Replace U9850, and the screen cable, and the connector(on the screen side and the logic board side) and it will usually be fine.