iPhone 13 Pro Max Cannot Boot caused by Audio issue repair.
Defect Phenomenon
The client sent an iPhone 13 Pro Max with the audio function issue to repair. After separating the two layers of the motherboard, the phone cannot boot and when checking under the Infrared Thermal Camera finds a component (an inductor) that is extremely hot.
Even though the inductor is extremely hot, when measuring the diode value it’s not short.
Only gets hot but not short, based on repair experience, normally it’s caused by the CPU damage, which is a really serious problem.
Troubleshooting Process
Use the tweezer to trigger the boot process, and as we can see from the DC power supply machine, the current fix is at more than 1000mA, which is abnormal!
Besides, can feel an inductor also gets extremely hot. Check under the infrared thermal camera, the location of the chip is around here
Feel the heat and refer to the component distribution and bitmap, confirming it’s the inductor gets hot. However, just as the previous repair technician said, there’s no short on this inductor.
First, let’s check and confirm if it is possible the issue is caused by the power management IC damage.
Measure the small components around the PMIC, everything is fine.
Then measure the small components around the CPU.
After measuring, find a small capacitor that relative to the CPU power supply gets shorted.
Seems it’s the problem, then we’ll need to reball the CPU and then solder it back.
Wait… Just before we plan to resolder the CPU, when checking under the microscope, we had a new discovery.
There is a tin bridge connection between two small components.
Check on the bitmap, it’s relative to the CPU power supply.
We have no schematic of the iPhone 13 Pro Max yet, not very clear why this short will cause the inductor gets hot.
Anyway, let’s remove the joint tin bridge with solder wick and hot air gun slightly first.
After that, assemble the phone and test.
The phone can boot normally and the audio function also works normally.
Summary
Through it takes a long time to repair the issue, the root cause is very tiny, just need to remove the tin connection between two small components.
Lesson learned from this repair case, must pay attention to the small details, especially for the motherboard assembling and disassembling process, check carefully to avoid the tin bridge connection!
