Separate the motherboard, check the solder joints of the motherboard to see if there are obvious virtual solder joints, and then measure the solder joints from the motherboard to the upper layer. It is found that the main board has obvious solder joints falling off. After the solder joint is repaired, the measured resistance is normal. Re-attach the upper and lower layers, and repair the fault.
iPhone 12pro Max mobile phone can not be called out. It is detected that there is solder joint falling off on the main board. After repairing,welding is applied to the upper and lower layers, and the fault is repaired.