Chosen Solution
My sister spilled apple juice over her Early 2015 Macbook Air, and failed to switch it off immediately… I managed to disassemble and clean it by following these excellent instructions so it at least boots again, but the backlight is broken. When pointing a flashlight to the display, it looks as if the LCD itself is not damaged afaict. Searching the internet I found hints that it might be possible to fix this issue by replacing a fuse o a FET or a driver IC. Is this correct? Any hint where these components are located, and what are their specs? Or would it be better to replace the entire logic board? Thanks in advance, Albrecht. Edit: some (bad, created using a mobile) photos of the main board: the cleaned mainboard after re-installing. I noticed corrosion in two places, indicated by the red circles:
corrosion in the right location, close to the AirPort, before cleaning:
same place, after cleaning:
in the left location, close to the display connector, after cleaning (sorry, I don’t have a photo with the corrosion, i.e. before cleaning):
Apart from the broken panel backlight, the systems seems to be fully operational. I could log in, connect an external DP monitor, and test the following: OK are: keyboard (checked every key), keyboard backlight, trackpad, both USB ports, external monitor out (DP), Wifi, Bluetooth, internal speakers, headphone, microphone, camera, SD card reader.The battery is detected and charging (I guess I have to reset the SMC and re-calibrate it, though).
@albrechtd Your board is a 820-00165 and right away of interes is image number 4. All of those parts are part of the LCD backlight driver circuitry. I allowed myself to modify your image with the reference designation
Here it goes: Reference designator F7700 is a 3Amp 32 V fuse in a 0603 package Reference designator C8317 is a 1000pF 50V 5% capacitor in a 0603 package Reference designator C7799 is a 10UF 50V 10% capacitor in a 1210 poackage Reference designator C7797 is a 10UF 50V 10% capacitor in a 1210 poackage Reference designator C7796 is a 10UF 50V 10% capacitor in a 0402 poackage Reference designatorD7701 is a RB1060M-60G diode is a SOD 123 package LCD Backlight BOOST Reference designator L7701 is a 15UH 2.8A PIMB053T SM inductor LCD Backlight BOOST Reference designator Q7707 is a DMN5L06VK-7 Mosfet Array 2 N-Channel (Dual) 50V 280mA 250mW Bklt Enable Reference designator Q7706 is a FDC638APZ_SBMS001 Fairchild MOSFET -20V P-Channel 2.5V LCD Backlight FET Datasheets for Q7707 ansd Q7706 are avialble but let me know if you have trouble finding those. For now I’d start to see if there is power to the LCD backlight by the fuse and work my way around the components. Check the boost circuit for sure. This is what that circuit looks like
As a quick check you can do something like this: At backlight output, measured on pin 3 or 4 of the LCD connector, 0v means short to ground, blown fuse, or no LCD conected. Check that you see an image on the LCD, check backlight fuse, check board via from FET after fuse to boost coil.8v means no short to ground, good fuse, but no boosting. Check BKL_EN is 2.7 to 3v at voltage divider going to enable pin of WLED driver, check BKL_PWM signal exists.27v or higher means all good, but your LCD cable or LCD backlight itself is blown.
