IPhone 7 no network
IPhone 7 does not catch the network
How do I fix the network on seven? This question was addressed to Bgacenter by a phone repair master from Novosibirsk, who is engaged in modular phone repair. And for training in soldering and diagnostics of boards, he brought the network seven with him. Subsequent repairs were carried out at the soldering courses in the training center.
iPhone 7 network search
The story is as follows. The phone was dropped on the asphalt, and then the network disappeared. Failure of the network part can manifest itself in different ways, for example:
- the display says “No network”,
- the “network Search” label at the top of the screen,
- the phone finds / detects the operator and loses the network again after 5 minutes,
- LTE or other bands are not working,
- the phone doesn’t ring 112,
- no modem firmware.
In our case, when you turn on your phone, you will see a “No network” notification on the screen. All other functions work correctly. Going to the settings, we found that the modem does not have a firmware. We can immediately make a preliminary conclusion that the soldering between BB_RF and the contact pad is damaged. Most likely, the repair will consist of rolling the modem.
And to do this, you need to disassemble the smartphone.
The first thing that started diagnostics was a visual inspection of the Board using a microscope. The results of inspection for visual defects are as follows:
- The payment was previously soldered. The remains of flux and the absence of protective screens are a clear sign of repairs that were carried out. Sometimes the frame is missing.
- Water ingress, not detected. Moisture indicators are white and there are no oxides and corrosion, and dried stains.
- The system Board is not deformed. No cracks were found in the Board.
- Condition of the bushing, another step that should not be skipped when examining the Board.
- Traces of soldering and lack of compound on inductors L1810, L1811, L1812; installed in the PP_GPU_VAR line. The coils are installed next to the U0700, the CPU. Zillion x Work software is used to determine the relationship between chips. On the other side of the Board, the soldering of the c7602_rf capacitor installed in the PP_VDD_MAIN circuit was detected.
- The modem or BB_RF chip has not been repaired before. The compound is not damaged.
- It is very important to pay attention to the integrity of EPROM_RF when repairing the network. This chip is responsible for the operation of the network part of the phone. If the chip is chipped (the chip case is damaged) or replaced with another one, the network cannot be restored on such an iPhone.
- In the BB_RF power supply circuits, the actual operating resistances were measured, namely in PP_1V0_SMPS5, PP_1V0_LDO9, PP_1V8_LDO7, etc. The resistances in the lines are fully operational.
- To make sure that BBPMU_RF (modem power controller) is working, it is necessary to measure the voltage in the above circuits. When measuring the voltage corresponds to the specified in the scheme. When the voltage in the lines differs from the voltage measured in the same circuits on a serviceable donor Board, in this case, it is necessary to replace the modem power controller.
IPhone 7 repair
Subsequent repairs, this is a modem reball.
Run in the following sequence:
- We start with cleaning the compound around the perimeter of BB_RF. On my hair dryer, Quick 861DE ESD Lead Free, I set the temperature at 230 degrees Celsius and the air flow is about 30%. I clean the compound with A special qianli spatula and a dental probe. Be careful, there is a small distance between the processor and the modem, so the view is not very good and you can damage the tracks passing in this place. Another “bottleneck” when cleaning the compound is in the area of the l2301 coil installed in the PP_VDD_MAIN line. If this inductance is damaged, the phone will not turn on.
- Before soldering the modem, it is necessary to protect the CPU from high temperature. To do this, install a heat sink on it.
- It is convenient to start the blade under BB_RF from the side of the c3532 capacitor. And yet, the blade must be wound up in the horizon, so we remove the capacitors C3532, C3531, C1914, C1901, as well as the resistor R1306. Then we will return them to their place.
- We apply flux to the modem, I use a non-washing flux FluxPlus. I warm up the chip a little, so that the flux spreads evenly around the perimeter of the chip.
- I set the hair dryer at 320 degrees Celsius and direct the hair dryer to the modem being soldered. Temperature and air flow are individual parameters. They depend on the model of the hair dryer and soldering technology.
- While the Board is hot, we immediately prepare the contact platform. To do this, we apply FluxPlus and tin the “spots” with rose alloy. This reduces the temperature of the factory solder.
- Next operation, using the S-line braid, we collect the remaining solder on the contact pad. And with tweezers, we clean the compound around the perimeter, where it is not possible to fit the braid.
- Then, lowering the temperature of the Board, preferably to room temperature, with a cotton swab and BR-2 (technical gasoline “Kalosha”), we wash the Board from the remains of the flux.
- Once again, carefully inspect the contact pad, it is possible that as a result of soldering, the pins on the system Board were damaged. Damaged contacts will need to be repaired using UV varnish and a flashlight. And only then solder the modem.
- To check the quality of dismantling the chip, run the Board (intermediate diagnostics), the phone should start and write a network search. And if when soldering BB_RF eels the Central processor, the inclusion will not be.
- Preparing the modem. To do this, apply flux to the chip and solder all the contacts. Wash the BR-2 contacts on the Baseband.
- Then, using Bga paste and stencil, we form ball pins on the chip. I apply the paste with a metal double-sided spatula, and always RUB it with a cotton swab. If you do not use a cotton swab, most likely the contacts will turn out more than necessary and the modem may get stuck in the stencil. After removing the stencil, you need to heat the contacts with a hair dryer to form the correct shape. Again, we wash the modem with gasoline.
- Installing BB-RF. Apply FluxPlus to the contacts on the Board itself. Positioning the chip, by the key and by the distance relative to other chips. And solder. The temperature at the same time, on my hair dryer 310 degrees, the air flow is reduced to the minimum value. And remember about the heat sink on the CPU. Before soldering the modem, restore the removed binding, this is:
- Let the Board cool down. Use a special brush to remove the flux.
- Connect the system Board to the lab and check for a short circuit. LBP KZ did not fix, we conclude that the soldering was performed qualitatively.
- Fully assemble the phone. Connected all the cables, display and battery. Installing the SIM card. Click the Power button and wait for the device to boot successfully
- IPhone 7 is loaded to the desktop. Go to Settings-Cellular connection. The phone identified the operator.
- For verification, call 112 and your work number. The phone rings. The repair was completed successfully, on the BGA soldering courses.
Problems with the network in iPhone 7, not frequent repairs compared to sixes. Now you know how to fix the seven yourself if the phone has stopped catching the network. If you want to learn how to repair phone and tablet boards yourself, call Bgacenter and sign up for a soldering course.