Fix iPhone 12 Won't Turn On By Infrared Thermal Imaging Camera

Attributed iFixit repair guide for iPhone 12.

Apple iPhone 12 Moderate 50 minutes Guide 143015

Licensed iFixit integration

This attributed iFixit guide is displayed through Fixonic's recorded commercial API permission. iFixit remains the independent source and author of the procedure.

Step 1

Repair step

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Press the power button, and the phone won’t turn on. Connect the phone to power, but it still won’t turn on.
Disconnect the display. Power up the motherboard. Please note that the power-up time shouldn’t be too long. It can be seen that the current value is large. The motherboard has a large current which indicates the motherboard is short-circuited.
Next, we need to remove the motherboard and locate the faulty part for repair. Measure the diode value of the PP_BATT_VCC line with a multimeter. The diode value is 0. It can be confirmed that the PP_BATT_VCC line is short-circuited.
The PP_BATT_VCC line and the PP_VDD_MAIN line of the iPhone 12 are connected in series by an inductor. So the short-circuited PP_BATT_VCC line may also cause the PP_VDD_MAIN line to short-circuit.

Step 2

Repair step

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The old solution to repair the large current problem is through rosin detection. Through the melting of rosin, we can confirm the faulty part. Though the solution is cheap and effective, it has some shortcomings. The motherboard has to be covered with rosin, which is hard to clean up afterward.
In addition, we have to remove shielding covers on the motherboard for a thorough inspection. There is no doubt that the operation difficulty will be greatly enhanced.
Today, we will introduce a more advanced and effective way to look for a short circuit on the motherboard with the help of a Thermal Imager Camera. The thermal imager locates the part whose temperature is higher than the normal value via infrared radiation.
The thermal imager can detect motherboard electrical leakage within seconds. The faulty parts will be detected in no time once you put the motherboard under the camera, tremendously improving repair efficiency. While checking overall motherboard working conditions, the thermal imager can pinpoint faulty parts with high accuracy.
Furthermore, the thermal imager is an expert in detecting small electric leakage, short circuit, and other problems with easy and safe operation, substantially lowering the error rate.

Step 3

Repair step

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First of all, we put the motherboard on the working platform. Connect the black probe of the direct power supply to the ground, and connect the red probe to the PP_BATT_VCC line. The temperature in the top left corner has risen. The faulty part can be confirmed in the top left corner.
Open the bitmap. We can see that the PP_BATT_VCC line is not in the top left corner. Since the PP_BATT_VCC line and the PP_VDD_MAIN line are connected in series by an inductor, we can judge that the PP_VDD_MAIN line is short-circuited.
Through the inductors of the PP_BATT_VCC line, click on the other side of the inductors. The other side is connected to the PP_VDD_MAIN line. We can again determine the range of the faulty part.
It can be seen on the bitmap that the PP_VDD_MAIN line is on the logic board.

Step 4

Repair step

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Next, we separate the motherboard. Put the motherboard on the 170 °C Heating Platform to heat.
After the logic board has cooled, power up the logic board. Connect the black probe to the ground and connect the red probe to the PP_VDD_MAIN line. Through the thermal image, we can now confirm the faulty part. The capacitor is flawed with charring.

Step 5

Repair step

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Remove the capacitor and clean the bonding pad with PCB Cleaner. Measure the diode values of the PP_VDD_MAIN line and the PP_BATT_VCC line. The diode values return to normal. The short circuit fault has been eliminated.

Step 6

Repair step

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Then we reassemble the motherboard. Assemble the phone to test. The phone turns on normally. WiFi and baseband function well. The IMEI number can be seen. The fault has been eliminated.