iPhone 12pro Max mobile phone can not be called out

iPhone 12pro Max mobile phone can not be called out

Machine model: iPhone 12pro Max
Test results: the mobile phone can be turned on, all functions are normal, and Baseband chip IMEI can not be read.
Fault analysis: the functions of the mobile phone are normal, and the Baseband chip IMEI cannot be read, which proves that there is a fault in the lower layer of the mobile phone or pad break off in the middle layer.
First open Xinzhizao Soft and find Boardview of iPhone 2pro max. you can see that the main board of iPhone 12pro Max is divided into two layers and three sides, the upper a side and B side, and the lower layer a side.Generally, the fault of signal part is caused by the fault of lower layer.

iPhone 12pro Max mobile phone can not be called out Figure 1.

First, separate the upper and lower motherboards. After separation, check the solder joints of the motherboard to see if there are obvious Inveracious Soldering pad break off. Then measure the solder joints between the motherboard and the upper layer.

iPhone 12pro Max mobile phone can not be called out Figure 2.

After inspection, it is found that the main board has obvious solder joint falling off. After repairing the solder joint, measure Diode value is normal.Carry out welding again on the upper and lower layers, and repair the fault.