Macbook Air 2018 820-01521 no image

[MicroSMD Lab]

Hi, I need some assistance with this please. Came in with no image, initially I saw nothing on the screen but external display works. Then I saw an image with no backlight on the lcd. While testing the backlight circuit I noticed there was no longer an image on the lcd but the external display still works. Initially I had to disconnect the eDP cable for the external display to work, now the external display will work with or without the eDP cable connected.
Pin 3 on J8500 reads 12.8 ohms to gnd on diode mode with both + and - on gnd. R8502 is good. No visible corrosion on the board.
Not sure where to go from here.

[vvicky8610]

Re: Macbook Air 2018 820-01521 no image

check properly if not contact me i try to help you

[vvicky8610]

Re: Macbook Air 2018 820-01521 no image

CPUGT_GLx pins are not connected; so no matters the voltage there.

Pin 12 should have PWM signal; but ONLY when the chip receives that signal.
"Pins 12 on U7410 = 0.08 volts, but when I check pin 12 on U7100 this shows 2.4 volts"
Did you check the continuity?

As you found corrosion signs on graphics area, this should confirm iGPU damage.
You can put quality flux and heat CPU; before trashing the board...

[vvicky8610]

Re: Macbook Air 2018 820-01521 no image

Disconnect J6100/700 and check again lid signals; their should be 1.8V suposedlly...