A diagnostic guide for technicians with the references listed below. Measure with the right tools and follow safe working procedures.
A phone that will not charge often leads technicians to immediately suspect the connector. However, components should only be replaced after the charging circuit has been checked in sequence. According to guidance from MJPRO Indonesia, the IOPP method—Input, Output, Command, Protection—can help technicians trace the problem without relying on guesswork.
Measure the VBUS input
The first step is to measure USB_VBUS_C while the charger is connected. The voltage at this point should be at least 5V. A multimeter is used to determine whether voltage from the charger is present at the beginning of the charging circuit.
This measurement serves as the basis for the next checks. If USB_VBUS_C does not show at least 5V, the technician should focus on the input section before moving on to other circuits. If the reading is correct, the inspection should continue because normal VBUS voltage does not confirm that charging is taking place. Avoid touching other points with the probe to prevent a short circuit.
Trace the OVP and protection circuit
Once VBUS input has been confirmed, trace the OVP/protection section. Many designs include overvoltage protection in the charging circuit. If the OVP is damaged or the protection is active, the voltage may be blocked and not passed on to the charging IC.
Therefore, the presence of voltage at USB_VBUS_C is not enough to conclude that the charging circuit is functioning normally. The circuit must be traced systematically to determine whether the voltage stops at the protection section. This approach is safer than immediately heating the connector with a hot-air blower or replacing components without taking measurements.
Confirm the charging command
The charging IC requires a command or enable signal to begin charging. Without this command, current will not flow even if VBUS is normal and the voltage has passed through the OVP/protection circuit.
Technicians should not immediately conclude that the charging IC is faulty simply because the phone is not charging. Checking the charging command remains an important part of the diagnostic sequence. Following this sequence helps narrow down the location of the fault before any components are replaced.
Check the output to the battery
The final step is to confirm that the charging output reaches the battery connector. The indication is an increase in VBAT while charging. This check shows whether the charging circuit is producing an output to the battery.
If VBUS, the OVP/protection circuit, and the charging command have all passed inspection but the battery still does not charge, only then should the battery or its fuel gauge be suspected. The inspection sequence is VBUS → OVP/protection → charging command → output to the battery. This process helps technicians distinguish between input, protection, command, and output faults before deciding to replace the connector.
