A diagnostic guide for technicians with the references listed below. Measure with the right tools and follow safe working procedures.
Names such as VIO18_PMU, BQ25970_SDA, OVPGATE, and LCM_RST_1 often make it difficult for novice technicians to read schematics. According to guidance from MJPRO Indonesia, NET names should not simply be memorized but understood based on their category, IOPP role, inspection sequence, and measurement method. This approach helps prevent technicians from measuring control lines as though they were main supply voltages.
Start with the Input
In the IOPP method, inspection begins with the Input before moving to the Output, Command, or Protection. When a mobile phone cannot charge, VBUS is the starting point. This line is classified as an Input and is measured as DC Voltage, with a minimum value of 5V when the charger or adapter is connected.
This sequence is important because checking subsequent lines will be difficult to interpret if the input source is not functioning properly. Use the multimeter carefully and keep the probe tip from touching two points at once, which could cause a short circuit.
Distinguish Between Supply and Command
BQ25970_SDA is an I2C control line and belongs to the Command group. Inspection focuses on the pull-up or logic level and bus activity when the block is active. Measurements are taken after the input rail has been confirmed to be functioning properly, rather than treating BQ25970_SDA as the main supply rail.
SCL is paired with SDA and serves as the I2C clock line. Its role is also Command, so the focus is on the logic level and bus activity, not the supply voltage. Separating these functions helps technicians avoid incorrect conclusions simply because they detect voltage on a line.
Check the Output and Protection
After understanding the Input and Command, proceed to the Output side. On the battery side, the voltage should follow VBAT according to the charging mode. This indicates that the circuit's operating result is read as an output rather than an input source.
OVPGATE functions as an overvoltage protection gate and is placed in the Protection category. The fast-charging block also contains VCHARGE and PMID_1-6. Recognizing the function of each line ensures that inspection does not stop at searching for voltage but instead follows the relationship among the input, output, control commands, and protection mechanisms.
Applying IOPP to Fast Charging
In Fast-Charging Symptom Analysis (Ref U3648), the main areas of concern include being stuck at 5V, failed fast-charging negotiation, overheating, and a battery level that does not increase. These symptoms are traced through the relevant points in IOPP order rather than by moving randomly between measurements.
The practical flow is to confirm VBUS as the Input, check the output that follows VBAT, and then assess Command lines such as BQ25970_SDA and SCL after the input rail has been confirmed to be functioning properly. OVPGATE is examined according to its role as Protection. This sequence makes schematic interpretation more systematic, particularly for beginner to intermediate technicians.
