How to Diagnose and Repair Large Current Issues on iPhone – A Step-by-Step Guide

When repairing phones, technicians frequently encounter difficulties when attempting to identify and resolve significant issues. The intricate nature of smartphone components makes it challenging to pinpoint the underlying problem. Fortunately, modern technology has brought useful aids, such as the LINCSEEK Infrared Thermal Camera. This device has made the process of identifying and resolving significant current issues much simpler.

Detecting Faults with LINCSEEK Infrared Thermal Camera

The LINCSEEK Infrared Thermal Camera is an essential asset for phone repair. It allows you to assess the temperature of phone components and identify any potential short circuits on the PCB. Moreover, it can quickly pinpoint problematic parts, such as capacitors with short circuits or small current leaks of 5 milliamperes. With its vision and thermal modes, it obviates the necessity for a microscope, providing unprecedented accessibility for diagnostics.

Repairing an iPhone 11 Pro Max with Large Current

Step 1: Initial Assessment

1. Phone Won’t Boot: Our journey begins with an iPhone 11 Pro Max that refuses to power up. To start, lift the screen, disconnect the battery, and connect the motherboard with a power cable. A glaring sign is the ammeter displaying a current of 1 ampere without the boot-up sequence initiating. This suggests the issue lies within the main power supply circuit and related components.

Step 2: Diode Value Measurement

2. Battery Connector Test: We measure the diode value of the battery connector with a multimeter, yielding a normal reading of 314.

Step 3: Thermal Imaging

3. Thermal Imaging: Placing the motherboard on the thermal imager, we connect it to power. Oddly, we notice significant heat buildup around the NAND, even though the NAND is not part of the main power supply circuit. This prompts us to remove the motherboard for further examination.

Step 4: Logic Board Inspection

4. Missing Pads: Take out the logic board using the Heating Platform set to a temperature of 170 °C. Due to previous severe impacts, it is evident that numerous bonding pads are now absent.

Step 5: Isolating the Issue

Signal Board Check: We connect the logic board to power separately and find no significant current. This leads us to conclude that the problem likely lies within the signal board. Powering it up with multimeter probes confirms our suspicion, as large current is evident.

Step 6: Identifying the Culprit

Thermal Imaging Revisited: Placing the signal board on the thermal imager and supplying power, we observe rapid temperature of the regions surrounding U5000 rapidly rises to 80 °C.

Step 7: Repairing the Fault

Capacitor Replacement: The capacitors surrounding U5000 were tested using a multimeter and a short circuit was detected. Furthermore, one of the capacitors was discovered to be damaged during the measurement process. Subsequently, the damaged capacitor was removed and a new one was installed after applying Paste Flux. The Hot Air Gun was set to 380 °C to facilitate the removal of the capacitor. Following the replacement, the multimeter was used to measure again and the diode value returned to the normal reading of 446.

Pad Repair: Repair the missing pads and clean the tin on the bonding pads of the signal board and logic board using a Soldering Iron and Solder Wick. Remove the thermal paste and continue cleaning the bonding pads with PCB Cleaner.

Step 9: Reballing

Reballing: Determine the missing pads for repair by opening REFOX Bitmap. If some missing pads are grounded, there is no need for repair. Use a Sculpture Knife to scrape and reveal circuits of the remaining missing pads. Apply tin to the bonding pads using a Soldering Iron.

Position the Soldering Lugs and proceed with soldering using a Soldering Iron set at 380 °C.

Apply some Solder Mask to the bonding pads that have been repaired. Then solidify with a UV Lamp for 5 minutes.

After solidifying, remove excess solder mask with a Sculpture Knife to show the pads.Next, we reball the signal board. Apply a layer of low-temperature Solder Paste evenly.

Put the signal board on the 170 °C Heating Platform to heat. After the solder balls are formed and the motherboard cools, apply some Paste Flux to the bonding pads.

Align the logic board. Keep heating with the Heating Platform. After recombination and the motherboard cools, connect the motherboard with a Power Cable. The motherboard no longer has a large current. Then trigger the boot-up with Tweezers. The boot current has returned to normal.

Install the motherboard. The phone turns on normally. The baseband is also normal.

Conclusione:

When dealing with phone repairs, it can be quite daunting to tackle major issues. Nevertheless, armed with the appropriate tools such as the LINCSEEK Infrared Thermal Camera and a methodical process, even the most difficult problems can be resolved. The following case illustrates how a combination of thermal imaging, diagnostics, and expert repair techniques can revive an apparently unresponsive iPhone. Hence, when confronted with a significant problem, it is crucial to bear in mind that a systematic approach coupled with the appropriate equipment can be the cornerstone of a successful repair.