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| IPhone 12 Pro Max No IMEI and missing Modem Firmware | |
|---|---|
| Device | iPhone 12 Pro Max |
| Affects part(s) | Motherboard |
| Needs equipment | Soldering Iron, Hot Air Station, Microscope, Multimeter |
| Difficulty | ◉◉◉◌ Hard |
| Type | Soldering |
Problem description
The Phone turns on but you are unable to find mobile service and there is no IMEI when dialing *#06#
Symptoms
- No IMEI when dialing *#06#
- No modem firmware
Diagnostic Steps
When you have a case like this, it means that the Baseband CPU is not talking to the CPU, this can be because of a missing voltage, a short, a bad solder joint under the CPU or the Baseband CPU, or a ripped pad between the two motherboards.
The most common issue is a disconnection between the top and bottom boards.
The first step before separating the motherboards is to check the voltages generated by the Baseband PMU, for this we will check a few test pads that are under the motherboard.
We need the following voltages for the Baseband CPU to work:
- PP_0V75_SMPS1_6 VOLTAGE=0.752V
- PP_1V22_SMPS2 VOLTAGE=1.224V
- PP_0V82_SMPS3 VOLTAGE=0.824V
- PP_1V9_SMPS4 VOLTAGE=1.88V
- PP_0V75_SMPS5 VOLTAGE=0.752V
- PP_0V75_SMPS7 VOLTAGE=0.752V
These lines can only be measured with the iPhone turned ON.
The next thing to do is to split the boards.
The first thing you should do after splitting the boards is to check for any ripped pads, if you have any you need to check with a program like ZXW and see where that line goes.
Test with a tool similar to iSocket and turn on the phone and see if IMEI is back and modem firmware is also displayed, if it is all you have to do is to reball the motherboard.
Check diode readings of both the top and bottom boards, use a tool like ZXW, check every line that connects to the Baseband CPU, if the expected value is for example 0.500 and you get 0.000 it means there is a short, inject a small amount of voltage and see what heats up hopefully not the baseband CPU since we cannot swap this component. If you get OL on a line while it should have 0.500 it means that there is maybe a solder crack or a ripped pad under the chip.
If you have any of the voltages about missing and they are not shorted, don't assume the Baseband PMU is bad, it can be because of a missing signal from the top board, so before replacing anything always try and test the board on a tool like iSocket.
Repair Steps
The first step is to split the motherboard
If any of the PMU voltages are shorted, inject a small amount of current with a DCPS and monitor what component gets hot under a thermal camera.
If the phone works fine on a tool like iSocket all you have to do is to reball the motherboard.
If you measure a point of the motherboard that goes to under the Baseband CPU, you have to reball this component, this is a very difficult process since the component is glued to the board, it is recommended to practice on scrap boards before attempting to reball this component on a customer device.
The Baseband PMU is also glued to the motherboard, it is also recommended to practice on scrap boards before attempting to reball this component on a customer device.
Final Testing
After reballing the motherboard, insert a SIM card and ensure the phone is able to find a network.
Check if the 4G signal is good and stable.
Check if 5G Signal is good and Stable.
Make a phone call.
Also, make sure to test every function of the device, since a bad solder joint on a pad between the top and bottom boards can sometimes occur.
Make sure the device doesn't randomly reboot.