Apple iPhone 12 Pro MAX suddenly lost the signal, and changing the card is not good?

Apple iPhone 12 Pro MAX suddenly lost the signal, and changing the card is not good?

The actual fault is that the phone can’t be called because there is no base band, because Apple is above X.mobile phone They are all designed with a double-layer motherboard, and the base band is in the lower layer, so we can directly disassemble the machine for layering, which is caused by virtual welding of the upper and lower layers. After planting tin on the lower layer and attaching it to the upper and lower layers again, it is confirmed that there is no short circuit, and the installed button screen is booted into the system and found that the base band already exists, and the serial number is normal.

“Machine model” Apple iPhone 12 Pro MAX

[Fault phenomenon] No base band

[Maintenance process] I received a machine sent by a customer for repair, and the model is Apple iPhone 12 Pro MAX. The customer said that there was no signal during normal use, and it was impossible to change several cards. Later, the card was inserted without service. I don’t know what happened. Just bring it to us to see what the problem is.

Apple iPhone 12 Pro MAX without base band figure 1

After receiving the machine, there is no setting about the card modem of this machine, and there is no serial number in the input *#06#, so the actual fault is that the phone can’t be called because there is no base band. Because Apple phones above X are designed with a double-layer motherboard, the base band is in the lower layer, so we can directly disassemble the machine and layer it, and observe that there is no trace of repair in the lower layer after layer, and the thermal conductive silicone grease is still there. We have made a circle of base band power supply and base band CPU power supply, and found no obvious short circuit.

We cleaned the upper and lower pads, clamped them with a test stand and tested them, and found that the base band had come out. Because the motherboard had not been dropped, flooded and repaired, we thought it should be the lack of base band caused by virtual welding of the upper and lower layers. After planting tin on the lower layer and attaching it to the upper and lower layers again, it was confirmed that there was no short circuit, and the installation button screen was booted into the system and found that the base band was already there, and the serial number was normal.

Apple iPhone 12 Pro MAX without base band figure 2

[Maintenance result] Install the motherboard into the mobile phone, and start the test. The mobile phone is normally booted into the system, and the functions such as charging, WiFi, voice, compass, vibration and telephone are normal. The maintenance is over here.