iPhone 12 Pro Max Not Turning On Issue Repair
Model: iPhone 12 Pro Max
Announced: 2020, October 13
Defect Phenomenon
Received an iPhone 12 Pro Max, and the cosmetic of the phone is very new, the customer just bought this phone 2 months, and even the original factory screen protective film has not been removed yet.
The client said the phone just suddenly blacked out and cannot boot again when playing Tiktok. But there is no water or drop damage… Return to the Apple official center and been told the phone was repaired by the 3rd party, OUT OF WARRANTY!
Troubleshooting
First, separate the screen carefully, and try to keep the original waterproof seal sticker without damage. Recover the deformed sticker with the tweezers slightly, so that after repairing the waterproof function can keep as good as the original phone.
Then remove the screen and check carefully, everything looks fine. The only tiny problem is a fingerprint sign left on the camera flex cable, which might caused by the after-sale check and repair.
Then protect the camera and dot projector with anti-static tape.
（This is a good repair habit that repair technicians should have）
After that, connect the motherboard with the DC power supply machine and trigger on to have a test.
The current just jumped a little bit and the current value keeps shaking, the phone cannot be booted. This means, the motherboard with some short damage.
Based on repair experience, the issue has a great chance is caused by the power supply of the NAND chip with a problem. This is also a common issue for generations of iPhone models.
Let’s measure the diode values of the NAND chip under the microscope. After the measurement, there is indeed a short circuit phenomenon.
Then in order to locate the exact shorted component, let’s check the motherboard under the thermal imager
Apply a 1.8V voltage on the suspicious rail that with short, we can see the short component easily
Once confirmed, we can just tick off it directly. Put the motherboard on the PCB holder, then heat it with the hot air gun slightly, and remove it with tweezers when the tins on the pads get melted.
* Before this, we can remove the foam sticker around the connector. After the operation, we can put back the foam, so that the motherboard can look as new as possible. Besides, the foam can also keep protecting the connectors from water or drop damage.
Then assemble the phone to have a test, and it can boot normally.
And test all the functions are also OK.
Tips
1. What is the shorted component?
It’s a filter-type capacitor, which can be used to stabilize the power supply for the chip to avoid fetal abnormal current damage to the chip.
The reason why this component easy to gets damaged by the abnormal current and voltage, is because of the comprehensive reasons like the system, circuit, chip itself, etc.
2. Why do we just remove the shorted capacitor?
Because of the process problem, if we solder back a new capacitor, it may affect many other chips when heating the motherboard with the hot air gun. So leaving it is better than soldering back with a new one.
The iPhone 12 Pro course will be launched soon, stay tuned to the REWA Academy to know the latest news.
