With R8442 at 0v, the backlight circuit is not being enabled.
Check the lid switch voltage to ground. This hall effect switch is inside the trackpad and often causes problems. With no power, also confirm that the interface cable contacts are clean and properly seated. IPA and a cotton swab are great to clean the cable contacts. If the logic board believes the lid is closed, the backlight will remain off.
PP1V8_S5_GPIOX_R ; power to the MUX (and the (tech) people)
PP3V3_S5_GPIOX_R
The above are used to deal with the display (U9801) and also the backlight enable signal.
PS: Have to check out for a few hours for the usual grocery shopping. Purchased some new security cameras for the business and the NEXT day they dropped the price. Really?? Price adjustment time
Hi, its the Display!! I found another A1990 here! and the display is intact. It works! So the board is defective from the display! Can you also buy the board?
For knowledge, watch this video where only the lcd is replaced for a macbook. This is a lower cost option but then is a longer servicing time for the procedure.
Do read the comments as well. Personally is on my things to do list but first need to fix up our company and take legal action against the guilty one. Lawyer meetings this week.
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