14. Check screen backlight circuit
Turn on your MacBook in a very dark room. Flash a touch on the screen. If you can see a dimmed image, your MacBook screen has a backlight problem.
The backlight circuit on the logic board is responsible for boosting the 12V voltage from the battery, to around 50V to power the screen LED light strip. If the voltage is low or absent, the LED lights will not be on, then your MacBook screen will black out. A faulty backlight circuit is a common problem in MacBook users described as “MacBook Pro screen not working but keyboard lit".
There are usually 14 capacitors to store the 50V energy to power the screen backlight as shown below
There are 7 capacitors on the top side of the logic board, and other capacitors on the bottom side. These capacitors are prone to short circuits.
If you see a small hair-like crack on one of the 14 capacitors, the capacitor is faulty, causing your MacBook Pro to go to a black screen.
You can use a soldering iron to remove the faulty capacitor, and your screen will work again. The remaining 13 capacitors should handle the power with no problem. Searching for a hair-like crack on the small capacitors is not easy. In our workshop, instead of looking for a hair-like crack, we use a multimeter to test if there is a short circuit in the capacitors. Then we inject a voltage to make the faulty capacitor hot and use a thermal imagery camera to pinpoint the capacitor. Once we have found the faulty capacitor, we use a hot air rework station to replace it. This is a basic skill of chip-level logic board repair.
A faulty graphics chip (GPU) is another common hardware problem causing your MacBook blank screen. As repairing or replacing a GPU is a highly skilled professional job, we won’t discuss it in detail in this guide. If you need more info on this topic, please see MacBook Pro GPU Repairs
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