IPhone12 has no baseband and no signal repair

IPhone12 has no baseband and no signal repair

iPhone12mobile phoneThere was no signal after the heavy fall, and the mobile phone was tested as baseband-free. Since the fault point has been found, the maintenance method is also very simple. Directly clean the residual solder on the middle and upper boards, replant the tin on the middle layer and attach it.

“Machine model” iPhone12

【 Fault Phenomenon 】 The mobile phone has no signal and no baseband (about the blank of modem firmware in this machine)

The customer described the failure of the mobile phone as a result of a fall, and there was no signal when it was picked up. After inspection by the official direct store, it was said that there was something wrong with the motherboard. If it was repaired, it was only necessary to pay for the replacement of the motherboard, but the price was too expensive. In the past, the customer repaired several mobile phones on our side and sent them here early this morning.

As soon as I heard the customer’s description, the mobile phone was a no-signal problem after it was dropped. According to the experience of repairing the no-signal machine in the past, it can be judged that this iPhone12 machine should be a no-signal fault phenomenon due to the lack of baseband after it was dropped.

IPhone12 maintenance without baseband and signal Figure 1

[Maintenance process] After receiving the customer’s iPhone12 mobile phone, turn it on and test it. As described by the customer (no signal), enter the settings of the mobile phone, general, and about this machine, and check that the modem does not see the relevant parameters, indicating that the fundamental fault of this machine is that there is no baseband.

Failure without baseband is usually caused by the failure of the RF module of the mobile phone to work normally, such as the damage of the baseband CPU, the lack of corresponding working conditions, and the disconnection or short circuit of the transmission line.

After communicating with the user, the mobile phone was disassembled and the iPhone12 motherboard was taken out. There was no obvious damage to the appearance detection motherboard. There is no baseband fault in the dropped iPhone12 mobile phone. Combined with previous maintenance experience, it is judged that the fault should be the virtual welding and dropping of the baseband part.

Apple iPhone12 adopts a double-layer motherboard design, and the RF part is on the lower motherboard. It communicates and transmits signals with the upper AP application board through the middle connecting board. It is also common that there is no baseband fault caused by virtual welding and dropping of the middle motherboard.

Maintenance of RF and baseband-related faults requires the use of a heating table or air gun to separate the upper and lower motherboards. After separation, check whether there is any problem with the lower and middle boards. The iPhone12 motherboard was layered with Xinzhi heating table. After layering, it was checked that there was no obvious virtual soldering and component dropping in the RF part, and there was no drop in the middle layer. This is a common situation of virtual soldering in the middle layer. It is only necessary to plant tin in the middle layer and then re-attach the motherboard.

IPhone12 maintenance without baseband and signal Figure 2

Now that the fault point has been found, the maintenance method is also very simple, directly cleaning the residual solder on the middle and upper boards, replanting the middle layer with tin and bonding it.

Almost all Apple mobile phones have adopted double-layer motherboards since iPhone X, and there will be more and more failures without baseband in the future. If the phone is not seriously dropped and there are not many points on the RF board of the phone, it can be repaired by flying wire. However, if the phone is seriously dropped and there are many points on the RF motherboard, the whole board bottom needs to be replaced, and the relative maintenance cost will be higher. In short, there is no baseband after the phone is dropped, and the motherboard is basically disconnected.

[Maintenance result] After fitting the motherboard, the installation test was carried out. The firmware version of the baseband modem in the mobile phone settings came out, and the signal of inserting the phone card into the mobile phone installation came out immediately. It was tested that the camera, WiFi and sound functions of the mobile phone were all normal, and the maintenance ended here.