Tag: iphone

In this article, we will address with the iPhone XR signal issues or “Searching for Signal” problem. We will explore how motherboard electricity leakage can cause this issue and provide a step-by-step guide on how to diagnose and fix it.

Preliminary Inspection

Before diving into the troubleshooting process, conduct a cosmetic inspection of the motherboard. Ensure it is not deformed or water damaged.

Assembling and Testing

Assemble the Phone: Begin by installing the motherboard and connecting the display assembly. Connect the battery connector with the DC Power Supply.

Current Reading: Check the current reading on the ammeter. If it’s abnormally high, it may indicate motherboard electricity leakage.

Diagnosing the Issue

Insert the SIM Card: After confirming the motherboard’s physical condition, insert the SIM card.

Power On: Press the power button to turn on the phone. Check for normal functionality. Verify ICCID and IMEI numbers in Settings > General > About.

Signal Search: The phone’s continuous signal searching indicates that the baseband circuit is functioning properly. It is likely that the issue lies with the signal power amplifier circuit.

Deeper Inspection

Disconnect the Power Supply: Turn off the power supply, remove the motherboard, and reconnect the battery connector to the DC Power Supply. Ammeter shows a current reading of 116mA. If the current reading remains high, it indicates motherboard electricity leakage.

Locate the Hot Spot: Touch the motherboard, and you may find that the signal power amplifier area is hot.

Removing Shielding Cover: Remove the shielding cover to facilitate closer examination of the area. Remove the dust-proof sponge from the board. Securely fasten the motherboard to the PCB Holder. It is important to consider applying low-temp solder paste along the side of the motherboard to decrease the melting point in this location.

Replacing Faulty Component

Apply high-temperature tape on connectors surrounding. Heat the four edges of the shielding cover using a Hot Air Gun set at 400℃ with an air flow of 3. Proceed to lift the shielding cover using tweezers. The burnt-out power amplifier IC U_QET_E will be visible. Utilize PCB Cleaner to clean U_QET_E.

Remove the IC: Heat with a Hot Air Gun at 360℃, air flow 3. Take down U_QET_E from the board carefully. We can see that U_QET_E and its bonding pad have been burnt. Apply some medium-temp solder paste to the bonding pad. Clean the bonding pad with Soldering Iron at 365℃.

Repairing Bonding Pads: Apply medium-temp solder paste to the bonding pad, clean it thoroughly with a rosin-soaked solder wick, and apply a UV-curable solder mask.

Jumping Wires: Clean the burnt Pin C2 and Pin D2 on the bonding pad. The relevant circuits of these two pins have also suffered damage. Pin C2 and Pin D2 serve as power supply pins for PP_VDD_MAIN. Since the circuits connected to these pins are burnt, it is necessary to establish a connection between them using C1208 and jumping wires. Apply UV curable solder mask to Pin C2 and Pin D2. Use a UV lamp to solidify it for 2 minutes. Then flatten the surface using a sculpture knife. Apply paste flux to C1208. Use 0.02mm Enameled Copper Wire to solder one end to C1208 at 365℃ using a Soldering Iron. Loop the other end of the wire around Pin C2 and Pin D2. Finally, apply UV curable solder mask to the soldered wire and solidify it under the UV lamp.

Soldering a New IC: Solder a new power amplifier IC in place. Ensure it’s positioned correctly and solder it with a hot air gun at 360℃ and airflow of 3.

Final Testing

1. Cool Down: Use the a Hot Air Gun to solder at 360℃ with an air flow of 3. Allow the motherboard to cool for 5 minutes before cleaning it with PCB Cleaner. Next, reconnect the battery connector to the DC Power Supply. The current reading on the ammeter should now be normal.

2. Assemble and Test: Reassemble the phone, insert the SIM card, and power it on. The phone powers on without any issues. If the signal bars are back to normal, the fault has been cleared.

Conclusion

This article addressed the “iPhone XR Keeps Searching For Signal” issue caused by motherboard electricity leakage. By diagnosing, identifying, and repairing the faulty component, we successfully resolved the problem. If you encounter this issue, follow the steps outlined in this guide for an effective solution.