IPhone 12 Pro Max cannot be started for repair

Machine model: iPhone12 Pro Max

Symptom: The phone cannot be switched on

Maintenance process:

A faulty iPhone 12 Pro Max machine was received. The fault description is that the phone can’t be switched on after normal use. In the test, the mobile phone cannot be started, and the current is high when the phone is powered on. This is usually caused by the short circuit of the secondary power supply.

The iPhone 12 Pro Max cannot be started for maintenance Figure 1

Open Xinzhizao, and find the power management chip in the annotation diagram.

The iPhone 12 Pro Max cannot be started for maintenance Figure 2

Determine the chip name as U3300 according to the dot map, and then go to the schematic diagram U3300 to measure the power output circuit.

The iPhone 12 Pro Max cannot be started for maintenance Figure 3

The iPhone 12 Pro Max is a double-layer motherboard design. The power chip is on the upper layer B side, which is easy first and difficult later. Power up first and then quickly touch the abnormal heating area of the motherboard.

The iPhone 12 Pro Max cannot be started for maintenance Figure 4

It was found that the fault was caused by a BOOST capacitor under the shielding cover beside the hard disk being short circuited. After checking the bitmap, it was found that the capacitor C4200 beside the U4200 was damaged. Replace the capacitor and repair the fault.