Customer mentioned his iPhone 6 Plus was dropped and the broken screen was changed. However, after a few days, it failed to auto-update. iTunes reports unknown error (56) when rooted.
First root it to make sure whether it reports error (56). After rooting and testing, it does report error (56).
In most of the cases, faulty camera circuits and NFC circuits will cause such a problem. Tearing it down and check the motherboard, the motherboard has been fixed. The previous maintenance have fixed NFC major control chip U5301_RF, its location is shown as the picture. Other chips are not fixed by observing its appearance.
In real repair cases, MIPI bus could cause error (56) report. First measure the diode data to ground of the MIPI bus of the front and rear camera by multimeter. These data are normal.
Customer said that he could use the iPhone normally before updating it, so the camera circuits have no problem. The major problem must happen at NFC circuit. Most people have not used this function, so they do not know whether it is normal or not.
NFC has two chips. One is major control chip (U5301_RF); the other is minor control chip (U5302_RF). In general, I first exclude the major control chip problems and then the minor control chip problems.
In rear repair cases, the dropped iPhone CPU and NFC signal circuits are easy to be disconnected. The NFC solder pad is easy to drop joints. So remove NFC major control chip U5301_RF. The solder pad does not drop any joints. Then measure the its diode data to ground to CPU data cable by multimeter and measure the resistance of U5301_RF. These data are normal. Now, I doubt that NFC major control chip U5301_RF is damaged. Replace the old one, but the problem remains the same. The diode data to ground of several data cables from NFC to CPU are normal, so CPU pseudo soldering problem can be excluded.
Next removing NFC minor control chip U5302_RF, I find some problems. The location of U5302_RF is shown in circuit diagram picture .
The solder pad of NFC minor control chip U5302_RF drops 3 joints, as shown in the picture. One of the pins is power supply pin and other one is ground pin.
Jump wires to connect these pins and assemble NFC minor control chip U5302_RF. Rooting goes on smoothly. Trouble is removed.
First root it to make sure whether it reports error (56). After rooting and testing, it does report error (56).
In real repair cases, MIPI bus could cause error (56) report. First measure the diode data to ground of the MIPI bus of the front and rear camera by multimeter. These data are normal.
Customer said that he could use the iPhone normally before updating it, so the camera circuits have no problem. The major problem must happen at NFC circuit. Most people have not used this function, so they do not know whether it is normal or not.
NFC has two chips. One is major control chip (U5301_RF); the other is minor control chip (U5302_RF). In general, I first exclude the major control chip problems and then the minor control chip problems.
In rear repair cases, the dropped iPhone CPU and NFC signal circuits are easy to be disconnected. The NFC solder pad is easy to drop joints. So remove NFC major control chip U5301_RF. The solder pad does not drop any joints. Then measure the its diode data to ground to CPU data cable by multimeter and measure the resistance of U5301_RF. These data are normal. Now, I doubt that NFC major control chip U5301_RF is damaged. Replace the old one, but the problem remains the same. The diode data to ground of several data cables from NFC to CPU are normal, so CPU pseudo soldering problem can be excluded.
Next removing NFC minor control chip U5302_RF, I find some problems. The location of U5302_RF is shown in circuit diagram picture .
The solder pad of NFC minor control chip U5302_RF drops 3 joints, as shown in the picture. One of the pins is power supply pin and other one is ground pin.
Jump wires to connect these pins and assemble NFC minor control chip U5302_RF. Rooting goes on smoothly. Trouble is removed.
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