The Complete Guide of How to Solve iPhone No Service _ Logic Board Repair
Use this guide to understand how to solve the iPhone no service problems. This includes logic board repair introduction of the iPhone 5s no service, iPhone 6 no service, iPhone 6 plus no service and iPhone 6s no service — all of which gives a simple and effective process that will prevent the no service phenomenon from ever happening again.
You can also reference this guide to repair the following problems:
iPhone No Service Example 1:
iPhone 5s is with no service, no IMEI serial number shown
Failure Phenomenon:
iPhone 5s is with no service after inserting SIM card, no IMEI serial number shown after dialing * # 06 #.
Maintenance Procedure:
There are IMEI serial number, modem firmware and ICCID in “about”, as shown in pic 1–1.
Pic 1–1 “About” Configure
Check “settings” → “operator”, there are China Mobile, China Telecom while no China Unicom (China Mobile, China Telecom and China Unicom are the operators in China, you can refer to the operators in your country, here is just an example for reference), as shown in figure 1–2. Under normal circumstances, the three operators including China Mobile, China Unicom and China Telecom should all be displayed.
Pic 1–2 “Operator” Configure
There are China Mobile and China Telecom in “operator” configure means that the signal channel circuit is working fine, the problem is usually caused by defective baseband CPU. Remove the baseband CPU and plant ball. After reloading the baseband CPU, then power on the iPhone 5S and find that no service problem has been fixed; now the problem has been solved.
iPhone No Service Example 2:
iPhone 6 no service occurred frequently, and no IMEI serial number shown
Failure Phenomenon:
iPhone 6 no service occurred frequently, no IMEI serial number shown after dialing * # 06 # when iPhone 6 is out of service.
Maintenance Procedure:
After booting iPhone 6, please go to “Settings” → “General” →” About “, there is IMEI serial number, but no IMEI serial number showed after dialing * # 06 # in the dial-up interface, you can then try to boot repeatedly for a few times, sometimes IMEI serial number displayed when dial *#06# in the dial-up interface. This failure is known as *#06# no serial number, which is usually caused by problems with the RFFE1 and RFFE2 buses in the baseband. These two groups of buses are used to manage the chips in the signal part for baseband CPUs. You can find the position of the RFFE bus in the point diagram is shown in pic 2–1, and its position in thecircuit diagram is shown in pic 2–2.
Pic 2–1 RFFE Bus in the Point Diagram
Pic 2–2 RFFE Bus in Circuit Diagram
The reason why this kind of fault phenomenon appears in a dropped iPhone 6, is basically because the RFFE1_DATA line to U1 is broken according to pic 2–2. Remove the baseband after disassembling the iPhone 6, prepare fly line to connect U1 to the test point on the back. RFFE1_DATA physical test point location is shown in pic 2–3.
Pic 2–3 RFFE1_DATA Physical Test Point Location
Prepare the fly line to connect the test point and apply green oil to the base band. The method of how to prepare fly line is shown in pic 2–4 and pic 2–5.
Pic 2–4 Fly Line on CPU Baseband and Apply Green Oil
Pic 2–5 RFFE_DATA Test Point Fly Line and Apply Green Oil
Assemble the main board and screen together, then start testing for days, iPhone 6 no service never happen again, this problem has been solved.
iPhone No Service Example 3:
iPhone 6 no service, no IMEI sercial number shown when dial *#06#
Failure Phenomenon:
No IMEI serial number shown in a dropped iPhone 6 when dial *#06# while the IMEI serial number could be found in “about” page.
Maintenance Procedure:
This problem is caused by the not working RFFE bus of baseband, because the U1 of CPU baseband loose connection after mobile phone drop. The position of U1 in the point diagram is shown in pic 2–6.
Pic 2–6 U1 in the Point Diagram
When there is no IMEI serial number in a dropped mobile phone. It is generally used to remove the CPU baseband to see if the U1 is dropped, and then test the ground impedance value of U1, U2, U5 and R5.
Remove the baseband CPU after disassembling the iPhone 6, and then find out that the U1 and V1 loose welding, as shown in pic 2–7. This problem caused by the U1 welding loose, in this case, the baseband CPU cannot communicate with the peripheral that lead to no serial number shown when dial *#06#.
Pic 2–7 U1 Loose Welding
First, scrape the wire that connect U1 and V1 until copper appears, it is shown in pic 2–8.
Pic 2–8 U1 and V Circuit
Then use two enameled wire to connect the welding loose U1 and V1, after that complete the enameled wire welding, as shown in pic 2–9.
Pic 2–9 U1 and V1 Fly Line
Complete fly line and apply green oil, reload the base band CPU and assemble the cellphone, then start testing to see if any signal problem still occurred, you will find everything is fine on the iPhone 6, the problem has beem solved.
iPhone No Service Example 4:
No IMEI serial number shown in iPhone 6 after the cellphone drop
Failure Phenomenon:
No serial number appears when dial *#06# after cellphone drop.
Maintenance Procedure:
The problem is usually caused by the RFFE break, you can disassemble the mainboard first and then remove the CPU baseband, there are some empty spot found on the bonding pad, what’s more, the U1 and V1 also loose welding, it is shown in pic 2–10.
Pic 2–10 U1 and V1 Loose Welding
Use fly line to connect from the welding loosing U1 to the RFFE test point on the back of the main board and apply green oil, then weld the CPU baseband. The fly line complete method is shown in pic 2–11 and pic 2–12.
Pic 2–11 Fly Line to Connect U1 and the RFFE Test Point
After fly line completed, reload the CPU baseband (shown in pic 1–12), you will find the signal problem already fixed.
Pic 2–12 Fly line complete and reload CPU Baseband
iPhone No Service Example 5:
iPhone 6 is with no service when insert SIM card
Failure Phenomenon:
No service notification on iPhone 6 when insert SIM card.
Maintenance Procedure:
First, let’s go to “settings” → “general” → “about”, we can find IMEI, modem firmware and ICCID, but no IMEI serial number appears when dial *#06#. Then we can find the measuring point of RFFE1 is PP3170_RF and PP3171_RF when checking PCB bitmap. RFFE1 bus measurement points are shown in pic 2–13, and their physical location is shown in pic 2–14.
Pic 2–13 RFFE1 Bus Measuring Point
Pic 2–14 The Location of The Measuring Point of The RFFE1 Bus
Check the ground impedance value of the RFFE1 bus, we find that the ground impedance value of PP3171_RF is higher than normal value, then go ahead to remove the baseband CPU, we notice that the ground impedance value of U1 is infinite. Scrape the wire near the U1 and use fly line to connect the welding loose U1, as shown in pic 2–15. After all these procedure complete, the ground impedance value of U1 back to normal.
Pic 2–15 U1 Fly Line
Put tin on baseband CPU (shown in pic 2–16), and then weld the baseband CPU to the mainboard.
Pic 2–16 Put Tin on Baseband CPU
Use an oscilloscopec to test the value of PP3171_RF, find that its RFFE1_DATA back to normal, as shown in pic 2–17.
Pic 2–17 RFFE1_DATA Wave Form
Test the the value of PP3170_RF, find that the wave form of the RFFE1_CLK back to normal, as shown in pic 2–18.
Pic 2–18 RFFE1_CLK Wave Form
Assemble the mainboard and screen together, after testing the iPhone 6, everything is fine, the problem has been solved.
iPhone No Service Example 6:
iPhone 6 plus call failed sometimes, or sometimes with no service
Failure Phenomenon:
Sometimes iPhone 6 plus call failed — that is, a call failed even with signal; when the signal is extremely unstable during charging.
Maintenance Procedure:
This failure is mostly caused by two issues, one is the problem of RF power supply chip and the U5411_RF; also, U5411_RF could be damaged or the working condition is not satisfied When charging, the signal unstablity is basically the damage of the physical location of U5411_RF is shown in pic 3–1.
Pic 3–1 U5411_RF Physical Location
First, test ground impedance value of the testing points in the two signal lines of RFF3 and the two power supply of U5411_RF. You can measure them in the position shown in pic 3–2.
Pic 3–2 Location of the RFF3 testing point and the two power supply of U5411_RF
The inductance is distorted when the pen touches the L5408_RF inductance lightly when measuring the voltage, and the two ends of the inductor are very black, as shown in pic 3–3.
Pic 3–3 L5408_RF Location
After unplugging the inductor, use tin to replace the inductor so to keep the connection, then power on the iPhone 6 plus and test the functionality of signal and phone call, if testing results are OK, the problem has been solved.
iPhone No Service Example 7:
iPhone 6 plus with no IMEI serial number shown when dial *#06#
Failure Phenomenon:
The iPhone 6 plus shows searching for service, no IMEI serial number shown when dial *#06#, while the IMEI serial number shown in “settings” → ”general” → “about”, and the phone keep searching for service.
Maintenance Procedure:
“No SIM Card” notification showing after you power ON iPhone 6 Plus when there is no SIM Card inserted. The “No SIM Card” notification helps us understand that the modem firmware is indeed in the “about” (refer to pic 3–4), which also means there is baseband in cellphone.
Pic 3–4 Modem Firmware in “About”
The modem firmware number shown in “About” means that there is baseband, if no modem firmware shown in “about” it means there is no baseband, do not insert SIM card and then access dial-up interface to input * # 06 # directly, under normal circumstances, IMEI serial number will be shown same as what you can find in “about” interface.
In this iPhone 6 plus, no IMEI serial number shown when dial * # 06 #, since we’ve already found out that there is baseband in this phone, in this case, no need to consider if it’s caused by the baseband, mostly the problem is caused by the RFF3 bus of baseband, there are four test points under the hard disk, as shown in pic 3–5.
Pic 3–5 Location of The RFFE Test Point in The Bitmap
Currently the copper of the 4 testing points on main board are still covered by materials, you will have to scratch it until copper could be found or use pen tip insert into the testing points and measure their ground impedance value. Under normal circumstances, the ground impedance value should be 300–400, after testing the 4 points, the ground impedance value of RFFE2_CLK is 750 (as shown in pic 3–6), it is much higher than the normal.
Pic 3–6 RFFE2-CLK Testing Point
It is obvious the RFFE2_CLK signal line has problem, and the ground impedance value 750 should be from the baseband CPU. Therefore, it is necessary to exclude the problem of the disconnection of the baseband pad, as the normal ground impedance value of is about 400, and the value of RFFE2 is from the DSM amplifier, this problem could be judged to be the DSM amplifier U_DSM_RF virtual welding. The physical location of the DSM is shown in pic 3–7.
Pic 3–7 The Physical Location of The DSM Amplifier
After reloading the DSM amplifier, the ground impedance value of RFFE_CLK back to normal as 380. The IMEI serial number could be shown after dialing *#06#. The signal of mobile phone is OK when SIM card inserted. Signal is fine after several days testing, the problem has been solved.
iPhone No Service Example 8:
iPhone 6 plus is out of service after falling, it has been repaired for several times already
Failure Phenomenon:
The iPhone 6 plus is out of service after falling, it has been repaired several times but the problem has not been solved yet, no IMEI serial number shown when dial *#06#.
Go to “settings” → “general” → “about”, there are IMEI serial numbers, modem firmware, WIFI address, Bluetooth and ICCID, as shown in figure 3–8.
Pic 3–8 “About” Interface
Maintenance Procedure:
The problem is mainly caused by the following reasons: no baseband (no IMEI, no modem firmware), no SIM card recognized (no ICCID), and RF circuit problems. If no service occurred in the broken mobile phone, it is generally caused by the components virtual welding or circuit opening.
According to above phenomenon, the problem is caused by the RF circuit. Use multimeter to measure the main test points, check to see if the ground impedance of PP3170_RF testing point is larger than the normal value of 0.406. The location of PP3170_RF measurement points is shown in pic 3–9.
Pic 3–9 Location of PP3170_RF Measurement Point in Bitmap
As shown in the schematic diagram, the PP3710_RF test point is the clock signal RFFE1_CLK of the RFFE bus, which is output from the baseband CPU, as shown in pic 3–10.
Pic 3–10 Baseband CPU RFFE Bus Circuit Diagram.
Check the PCB bitmap first, as you can see the RFFE1_CLK signal connected to multiple chips. The components that connect to RFFE1_CLK are shown in figure 3–11.
Pic 3–11 Location of Components that Connected to RFFE1_CLK in Bitmap
After the chips are removed, we found that several chip solders are out of their position. Then use fly line to connect the out of position chips, as shown in figure 3–12.
Pic 3–12 RFFE2_CLK Fly Line
Fix the fly line by applying green oil and weld the chips back to their positions, after that the ground impedance value of the test points are back to normal, now please assemble the phone back to a whole part and dial *#06#, you can find IMEI serial number shown successfully.
After testing, the signal of iPhone 6 Plus will go back to normal when the SIM card is inserted. Also, the phone call functionality will go back to normal, the problem has been solved.
iPhone No Service Example 9:
iPhone 6s is out of service at most of the time, weak signal comes back occationally
Failure Phenomenon:
iPhone 6s no service occurred frequently, most of the time there is no service in this iPhone 6s, occasionally the iPhone 6s is with weak signal.
Maintenance Procedure:
This fault occurred in normal us of iPhone 6s. It is basically because of the damage of the RF chip in iPhone 6s, it’s common failing in iPhone 6 and iPhone 6s. The physical location of the RF chip is shown in pic 4–1. If reinstalling RF chips does not work, the problem will only be solved replacing radio frequency chips.
Pic 4–1 Location of The RF Chip in The Motherboard
After disassembling the iPhone 6s, visually check the main board first, and check if a small capacitance C4112_RF on the edge of the RF chip was displaced, as shown in pic 4–2. And then check the circuit diagram to learn that C4112_RF is B20, B26, B27 frequency band. The absence of this capacitor does not affect the use of mobile phone in China — you can remove this capacitor directly. (Please confirm the frequency band of the capacitor when performing this step)
Pic 4–2 C4112_RF Displaced
After replacing the RF chip, power on cellphone and test the function, insert the SIM card and confirm that the signal back to normal, so the problem has been solved.
There are some failures caused by RF chip such as iPhone no service and signal instability (sometimes with signal while sometimes no signal). The most efficient way to do maintenance work is to change the most frequently broken chip and then check the other components. The most frequently damaged components of the iPhone 6S is 2G amplifier and RF chip, their locations are shown in pic 4–3.
Pic 4–3 Location of 2G Amplifier and RF Chip in Bitmap
iPhone No Service Example 10:
iPhone 6s is out of service after dropping in the water
Failure Phenomenon:
The iPhone 6S dropped in the water, after drying the iPhone 6S, there is no service after inserting SIM card.
Maintenance Procedure:
Power on to test the iPhone 6S first, and find that there is no service after inserting SIM card while there is “operator” in “settings”. The phenomenon of “operator” in “settings” indicates that there is no problem with the signal receiving circuit, and the fault should be in the signal transmitting circuit. Teardown the cellphone and find that motherboard is corroded, as shown in pic 4–4.
Pic 4–4 Corrosion Diagram
Clean the corroded area and test the power supply of each chip. It is found that the ground impedance value of 2G amplifier power supply is infinite. After checking the technical drawings, the PP_VCC_MAIN should connect the 2G amplifier through a resistance R4501_RF, as shown in pic 4–5.
Pic 4–5 2G Amplifier Power Supply Circuit
The location of R4501_RF resistor in the PCB bitmap is shown in pic 4–6.
Pic 4–6 Location of R4501_RF in PCB Bitmap
Replace the R4501_RF and test the iPhone 6s, we find that the problem is still not fixed yet. In order to find out the problem, fly a fake antenna to identify where the damage is. Use a 10cm enameled wire to serve as a fake antenna and connect it to 2G transmission, as shown in pic 4–7.
Pic 4–7 Location of Flying a Fake Antenna in Bitmap
After flying the fake antenna, test the iPhone 6s to check if there’s no service phenomenon. If it exists then RF chip is damaged — replace it. The problem has been solved.
