"Diagnosing A Dead Mobile Phone For Beginners" Do you want to learn how to diagnose a dead mobile phone, do you want to learn how to troubleshoot dead mobile phone as a beginners. Are you searching for diagnosing a dead mobile phone, how to troubleshoot a dead mobile phone, how to repair a dead mobile phone, basics of troubleshooting dead mobile phones or cell phone troubleshooting and repair. If yes, Infoguide Ng has brought a complete step by step article that explain mobile phone repair and power circuit troubleshooting for beginners. This mobile phone repair article aimed primarily at beginners who may not possess professional-level troubleshooting tools. I will explain the basics of diagnosing a dead mobile phone, focusing on the primary and secondary voltage circuits. Specifically, this article cover locating the battery connector and tracing the Vbat voltage from the battery to the charging IC and then to the power manager IC, sometimes referred to as the VPH or VSY line. The article outlines troubleshooting steps, such as checking for voltage at key points like the power switch and using a multimeter to test the charging circuit's integrity, this article also explain when a component might need to be replaced or reballed.
This comprehensive article aimed specifically at beginners who may not possess advanced tools like a DC power supply.
Fundamentals of Mobile Phone Power Circuits.
When troubleshooting a phone that is not powered on, the first steps involve opening the device and locating the battery connector. It is crucial to understand the VBAT circuit, which refers to the battery positive line.
The Primary Voltage (VBAT)
The VBAT voltage is the main input of the mobile phone.
- The VBAT voltage comes in from the battery when it is connected to the PCB.
- At the VBAT jumper point (or the battery connector), if the battery is connected, you should measure approximately 3.7 volts or the exact voltage present in the battery.
- From the VBAT point, the voltage typically goes to the power manager IC or the charging IC, depending on the specific mobile PCB design.
Voltage Distribution and Conversion.
The path the VBAT voltage takes determines how the device's primary power section is structured.
1. Path through a dedicated Charging IC: In some mobile phones, such as chinese phone model discussed in this article, the VBAT voltage comes from the battery and goes directly to the charging IC.
- This charging IC is responsible for converting the primary voltage (VBAT input) to the secondary voltage (VBAT output).
- The secondary voltage is often known as the VPH or VSY line in most mobile phones, though it may be labeled as the VBAT output.
- This secondary voltage (VPH) is the power supply for the power manager IC (PMIC). The supply is necessary to switch on the PMIC and initiate voltage distribution to other parts of the mobile phone.
- The secondary output voltage usually comes out through a component known as the VPH coil (or inductor).
2. Path directly to the Power Manager IC (PMIC): In mobile phones that do not have a big, separate charging IC, the VBAT line goes straight to the power manager IC. In these models, the PMIC integrates the function of converting the primary VBAT voltage to the secondary VPH voltage.
Basic Troubleshooting Steps.
For beginners, troubleshooting involves checking specific voltage points to confirm the integrity of the power supply section.
1. Checking the Primary-to-Secondary Conversion
If the phone uses a dedicated charging IC:
- You must check for voltage at the VBAT input (often a capacitor near the charging IC).
- You must then check for voltage at the VBAT output (the inductor/VPH coil).
- If you get the VBAT voltage input but do not get any output voltage (VBAT output/VPH) when the battery is connected, it indicates that the charging IC is bad and needs to be replaced.
- In some cases, reballing the charging IC may solve the problem if the issue is an open circuit.
2. Checking the Power Key Voltage
A key step to confirm if the power supply section (the primary to secondary circuit) is working correctly is to check the power on voltage in the power switch (power key).
- If there is voltage present in the power key, it means that the primary-to-secondary circuit is functioning correctly. This is true whether the conversion is handled by a big charging IC or integrated within the PMIC.
- If you do not get voltage at the power key, and you have confirmed the input VBAT but lack the output VPH, you will need to replace or reball the charging IC.
3. Checking the Charging Circuit (Alternative Method)
The charging circuit's health is critical, as a bad charging circuit may prevent the phone from switching on. An easy way to check the charging circuit is:
- Connect the charger to the phone and disconnect the battery.
- Set your multimeter to the DC range (such as DC 20 or DC 200).
- Check for the charging voltage in the battery connector.
- If you do not get the charging voltage in the battery connector, it means the charging circuit is not okay.
- If the phone has no separate charging IC (meaning the charging circuit is integrated with the PMIC) and the charging is not okay, you may have to reball or change the power manager IC.
I believe this step by step article will help you to learn how to diagnose and repair a dead mobile phone.
