820-3662-A darkens the video after a time of use.

[iClub]

There are no signs of oxidation, the CPU heats up a lot, the voltages are normal from the measurements I made.
This 15' mac has no GPU.

Voltage: PPBUS_G3H 12.6V; 3.43V; PP3V42_G3H; 3.23V; PLT_RESET_L 3.33V;

 

[2informaticos]

Is backlight, or image problem?
Check the backlight output voltage.
Try known good compatible LCD assembly.

External video is good?