Defect Phenonenon
Received an iPhone 6s with drop damage, can not start up.
And try to connect with DC power and start-up, CPU get extremly hot.
Troubleshooting
First, since the phone is get damaged. We should check the cosmetic of the motherboard.
Disassemble the phone and check the motherboard under the microscope. Crack signs are found on the Wi-Fi chip and the little chip around it.
Obviously, the two chips are damaged and no use any more.
So we can remove the two chips with hot air gun first.
Then, test again with DC power supply to see if the CPU still hot or not?
- If the CPU hot phenomenon gone, then issue should be caused by the cracked two chips
- If the CPU still hot, then we need continue to test whether there is other damaged components
The test result is CPU still hot.
So we use multimeter to measure the components around CPU. After measuring, find the PP1V8_SDRAM get shorted. And as we can see from the Refox bitmap, there are so many components related with PP1V8_SDRAM.
The fastest and most cost-effective way to find out the heat (shorted) components is rosin insepction method.
Apply rosin on the motherboard first, then apply a 1.8V DC power on the proper test points.
We can find there are two small capacitors above CPU, the rosin on them get melted.
The melted capacitors (C2030/C2031) are filter type capacitor, so we can just take them off directly.
After taking off the two capacitors, then test with DC power supply again. The CPU hot phenomenon is gone.
Then we put back the new Wi-Fi module chip and the U_VOX_RF chip.
Let’s assemble the phone and test again, it can boot up normally and all the other functions work well.
Customer’s phone get fixed perfectly!
Summary
For the drop damaged phones, the repair is harder than water damage. As the problem might caused by inner PCB rail broken, chips poor soldering, or chips cracked as what we can see in this case.
But do not be afraid of failure, follow the normal troubleshooting process. There is still a chance to get the problem resolved. If you need to learn more repair skills and repair knowledge, welcome to visit REWA Academy to join us.
