Repair iPhone 6 cannot turn on after charging

Last night,  the iPhone 6 is charging.  Today, i want to use it,  but i found it cannot turn on.  After we check it,  the power supply was short circuit (power supply grounding)

Power supply short circuit is mostly from two groups of power supply problems: battery power supply(PP_BATT_VCC), charging tube output power supply (PP_VCC_MAIN). If there is one of the power supply grounding between them, the short circuit fault as the iPhone 6 will be caused.

First of all, we need to judge which group power supply causes the problem, measuring the battery power supply (PP_BATT_VCC) to check whether the battery interface is connected with positive and negative port, if not, it means the first group of power supply has no problem, on the contrary, it would be the first group power supply problem. The two groups power supply circuit picture are shown in picture 4-10-1.

After measuring the iPhone 6 device, we get to know the fault is the charging pipe output power supply (PP_VCC_MAIN). First, we offer artificial power supply in the second group power channel to see if the component is hot, but there is no element heating phenomenon. By checking on the schematic diagram, there are dozens of places through, so we need to dismantle the components one by one. Take off the charging tube U1401 and electronic switch Q1403 on the motherboard as shown in picture 4-10-2, the fault still exist.

Now we can only measure the internal resistance of components on the channel by milliohmmeter to see if there are any difference, after one by one measurement, we found that on the upper right corner of the main CPU, the C1552 internal resistance is 37 mOhm, the value is small.

The second group charging tube output power supply (PP-VCC-MAIN) channel diagram, as shown in 4-10-3.

Finally, remove C1552 by a soldering iron, the problem is solved.

Note: the C1597 next to C1552 is also easy to get a short circuit.