iPhone 6 Plus Cannot be Turned on with 70mA Constant Current
A few days ago, we received an iPhon 6 plus from customer, The problem is that it cannot be turned on and the constant current is 70mA after the customer fixed it by himself. The original problem was unresponsive touch. When soldering touch chip, the front camera socket dropped because the air gun had higher temperature. After soldering front Camera FPC Connector socket, I found that the front camera still could not be used. I blew the area near fingerprint socket. It cannot be turn on completely.
Customer only sent the motherboard, so I energize it and test. The constant current is 70mA and it stops.
Based on my experience, constant current stops at 70mA mainly because of the bus. I go on to measure the diode data of bus voltage. The data is normal. Many reasons can lead to turn on failure. If we want to narrow the problem scope, we can use root method. The customer agrees me to root. It reports unknown error (4005). Based on my experience, I know that CPU or temporary storage, as shown in the picture.
The major point of soldering CPU lies in the treatment to the top of the CPU lower board, as shown in the picture.
After soldering the CPU lower board, assemble the iPhone and test. The current is normal. I continue to assemble the temporary storage, finding that the current still stops at 70mA, which is abnormal. Obviously the problem lies in temporary storage, as shown in the following picture. Then I turn it on to test. All the functions are normal. Trouble is removed.
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