Let's talk about the leakage of Xiaomi's mobile phone motherboard.

Xiaomi's mobile phone motherboard leaks electricity and can be repaired.

A, no matter what mobile phone, the cause of the leakage fault, can be roughly divided into two kinds:

1, b Leakage: This kind of leakage means that there is leakage as soon as the power is turned on and the power button is not pressed. During maintenance, focus on the components on the B channel, which are generally caused by leakage of components such as power IC, power amplifier and B filter capacitor.

2. Load leakage: that is, there is component leakage on the power output path. In this case, when the power is turned on, there will be no leakage without pressing the power button, but only after pressing the power button (that is, the current is larger than that of a normal mobile phone). This situation is more complicated, first of all, because there are many components on the power output path and the circuit is more complicated. Secondly, sometimes the leakage component itself is not hot, but the power IC is hot, which makes some friends have a headache. 3. Power line leakage: This kind of leakage is very similar to Class B leakage. When the power supply is connected, there will be leakage. The power supply will not leak when it is removed, but it is still invalid. At this time, there must be leakage in the boot line. Generally, the capacitor of the boot line has leakage, so it can be removed. It may also leak to the ground.

Second, no matter what kind of mobile phone, leakage can be divided into two types according to current:

1, large current leakage: the current approaches or exceeds 100MA, and the leakage element is obviously heated, so it is easy to find the cause of the failure.

2. Low leakage current: the leakage current is less than tens of milliamps, and there are no obvious heating elements. Many friends have no good idea about this kind of fault, and generally adopt the "disassembly method" (that is, the "guessing method" to put it bluntly), that is, if you doubt which part is leaking electricity, you will disassemble it. If it doesn't leak after being removed, it is broken. However, there are so many mobile phone components, and some are rubber IC, or the leakage components are not big, just some small components such as capacitors and inductors, so the "wild guess method" has to give up and surrender.

Third, the solution:

For large current leakage (obvious heating of components), and the heating element is a leakage element, the heating element can be directly replaced. Anyone can do this, so I won't say it. Here, I focus on two kinds of headaches:

1, the load leaks, but it is the power IC that generates heat.

2, the leakage current is small, and the fever is extremely inconspicuous.

1, "load regulated power supply": the load is charged with leakage, but the power IC generates heat. I believe that everyone has encountered this situation. It is clear that the power IC is hot, but the power IC (whether it is new or moved from a good machine) still emits light correctly after several changes. This is caused by load leakage. This problem can be solved quickly by using the method of "load regulated power supply": the positive pole of the regulated power supply is connected to the output end of the mobile phone power supply circuit, and the negative pole of the regulated power supply is connected to the ground of the mobile phone motherboard. Then the regulated power supply is slowly adjusted from OV to the standard value of this power supply (for example, the standard value of VBB of 33 10 is 2. 8V), pay attention to observe the ammeter of the regulated power supply, and you can find out whether the road leaks electricity. If there is leakage in this circuit, you can use the "touch method" (showing high leakage current accompanied by obvious heating, that is, touching mobile phone components with your hands or lips) or the "cigarette lighter loosening method" (showing low leakage current accompanied by obvious heating, which will be introduced in detail later). These two methods can quickly judge the leakage components.

2. "Smoke scattering method": collecting a small leakage current is extremely inconspicuous. In this case, it is difficult to feel when touching mobile phone components with hands or lips, especially when the leakage is small components such as capacitors and inductors, which are difficult to touch with hands or lips. At this time, the "pine smoke method" can play its wonderful role: dip a 936 soldering iron in rosin, and then a pine smoke will appear on the soldering iron. When pine smoke is close to the motherboard of the mobile phone, it will adhere to the components of the mobile phone, forming a thin layer of white "rosin paste" (note that you can't use an ordinary soldering iron when smoking pine smoke, because the ordinary soldering iron is too hot, the pine smoke will evaporate soon, and it is not too late to smoke on the motherboard. If electric leakage is suspected, a layer of rosin paste can be pumped there. If you don't know where the leakage is suspected, you can pump the whole mobile phone board together. After fumigation, power up the mobile phone. When powered on, it can slowly rise from 0 V. If the current is too small, the voltage can be raised appropriately, but be careful not to be too high to prevent other components from burning out. During the boot process, pay attention to the components on the mobile phone motherboard. If any component leaks electricity, the white rosin paste on the component will melt and "show its original shape"-it is the real murderer of leakage!