Xiaomi 11 small current does not start, redo CPU failure is still the same

Xiaomi 11 small current does not start, redo CPU failure is still the same.

Xiaomi 11 doesn’t turn on the small current, and the peers have already done CPU, but the fault is still there, so let our maintenance master see what is going on.

“Machine model” Xiaomi 11

【 Fault Phenomenon 】 If the power is not turned on at low current, the fault of redoing CPU remains the same.

[Maintenance process] I received a second repair machine from a colleague. The fault was described as low current and it didn’t start. The colleague had already done CPU, but the fault was still there, so I sent it to us to study and see if it could be repaired.

After receiving the machine, we directly took out the motherboard and observed that the shielding cover of the motherboard had been removed, and the CPU had traces of redoing. As we all know, the common problem of Xiaomi 11 is nothing more than that the CPU virtual welding leads to a small current not turning on, and the redoing CPU can be 90% better, but this one may just be in the remaining 10%.

When the single board is powered on, it is found that there is no current, and when the power button is pressed, there is no short circuit between the battery voltage and the main power supply, and the voltage is also there. The power button also has a voltage of 1.8v How can it not trigger no current?

It is found that the inductance near the power supply is not short-circuited, and some small voltages also measure the nearby capacitance. No abnormality is found, so we have to remove the power supply and try it. When the power supply is removed and powered on, we find that there is still no current, and there is still no current when a new power supply is replaced. After maintenance, we are in trouble. We can only observe whether there is anything on the motherboard that we have neglected.

After inspection, it was found that a grounded resistor disappeared near the power supply.

Xiaomi 11 is not turned on at low current, and the CPU fault is still repeated. Figure 1.

Xiaomi 11 is not turned on at low current, and the CPU fault is still redone. Figure 2

openschematic diagramIt is found that this is an electric battery ID information identification resistor with a size of 100K. If there is a problem with the signal BATT_ID, it will cause battery information identification errors, so that the power supply can’t work normally. No wonder there is no current. Then we find a resistor with the same size of 100K to supplement it, and the current will appear when it is powered on again, and the system can also enter normally when the screen is turned on.

Xiaomi 11 is not turned on at low current, and the CPU fault is still redone. Figure 3

[Maintenance Result] Install the motherboard into the.mobile phoneIn the power-on test, the mobile phone is turned on into the system normally, and the functions of charging, WiFi, sound, compass, vibration, telephone and so on are normal. The maintenance is over here.