How to fix iPhone XR no baseband issue repair case sharing.
Model: iPhone XR
Defect Phenomenon: No baseband and cannot be activated after forcing recovery
Tips: for the phone with no Baseband or no signal issue, please do not hurry to restore or recover!
If the phone has been restored or recovered before repairing, but the issue can not be fixed,
then your phone will be a brick and with no use.
However, the phone without a restore or recover process, even cannot be fixed,
but at least you can keep it as a game machine.
Repair Process
Received the phone from the client, no baseband, and the phone has been fixed by another repair shop before.
Disassemble the phone and take out the motherboard, found
- The shielding cover on the baseband chips has been removed,
- The NAND chip also has been resoldered and then sealed with some black glue.
Check the baseband CPU U_BB_K, the small capacitors, and resistors around it have turned black because of the corrosive damage by the poor quality solder paste.
Based on repair experience, apply a little bit of rosin and heat with a hot air gun to resolder the small chips around the baseband CPU. By doing this, small components (capacitors and resistors) will be soldered better.
Then clean the motherboard with PCB cleaner.
After that, remove the Baseband CPU chip and check the pads on the PCB.
After removing the U_BB_K, we can see some problems
- There are some scratch marks around the Baseband CPU chip, it should be caused by the sculpture over scratching. But luckily, no damage to the PCB layers.
- The tin paste is the low-temperature solder paste, which with very low melt temperature and low hardness.
Then let’s resolder the baseband CPU with medium temperature solder paste, and solder it back. Restore with iTunes then test, the defect phenomenon still remains the same.
Measure the diode values of the Baseband CPU power supply rails, they are also OK.
Check the transceiver IC, it seems the chip has also been fixed before. So we will try to replace the U_XCVR_K with a new one.
After replacing the transceiver IC with a new one, then restoring it with iTunes the baseband and signal function back to normal.
Summary
The issue is caused by the Baseband CPU and transceiver IC, the previous repair shop repaired the two parts. But because of the poor soldering handwork and poor-quality solder paste, the issue does not get fixed thoroughly.
Lessons learned from this case, do more handwork practice if you want to be a repair expert, and use qualified repair materials, do not solder the Baseband chip with low-temperature solder paste!
