Xiaomi Mi 8 motherboard disconnected no wifi
Xiaomi Mi 8 motherboard disconnected no wifi
Keeps rebooting automatically, can’t get into the system, ask for advice. Maintenance white boy, no ideas, afraid to mess with it.
I. Description of the phenomenon, problem
The fault on the maintenance work order for the phone does not charge, plug USB does not respond.
Second, the key process, root cause analysis
1. As the motherboard for the market repair, dismantling the motherboard before doing any maintenance actions, first consider whether the motherboard is burned out or customer plug and play Damaged USB interface phenomenon, that is, the first visual inspection of J1602 (USB interface) and the surrounding components appearance, found no abnormalities.
Considering that the phone does not have any response when plugged into the USB, the motherboard fault for not charging, do not identify the USB, it is likely that USB The interface has open pins or path open phenomenon. But the measurement of the USB interface of the various pins to ground impedance, and normal board comparison are normal.
3. Since the ground impedance is normal, the motherboard is no problem with the channel, but does not mean that the motherboard voltage and power supply are normal, so view the circuit diagram , through the circuit diagram USB interface pin by pin towards the measurement of each pin path voltage.
Huawei P8 Youth Edition Mobile 4G does not charge, does not identify USB repair Figure 1
4. The measurement process and corresponding measurement points are shown in the following table.
Huawei P8 Youth Edition Mobile 4G does not charge, does not recognize USB repair Figure 2
Visible measured voltage values are also normal, but considering the VBUS_USB to charge management chip (U201) between the Also through a field effect tube Q1602, this field effect tube is to control the VBUS_USB voltage to protect U201 So we measured the voltage of VCHG (C1622) and found that the voltage is 4.23V, which can be seen after Q1602. The voltage is reduced by 0.7V. Consider the voltage reduction of the control due to Q1602 body damage.
Conclusion, solution and effect
After replacing Q1602, the phone charges normally and identifies USB normally.
IV. Summary of experience, preventive measures and standard recommendations
The two faults of not charging and not recognizing the USB are often both present at the same time, and when fixing such faults be sure to link them together for a comprehensive repair. Location. The key point of such failure is about the USB pin measurement, step by step in accordance with the pin measurement anomaly, against the wiring diagram for Find out why.
Faulty model]: iPhone 6 Plus
Fault】：Play sound display headphone mode
The customer description says that when playing sound, the display is headphone mode, no external playback.
Headset mode, that is, the system has been identified headset access, tail plug J1817’s headset insert detection signal HPHONE_TO_CODEC_DET_CONN abnormal, generally resulting in this phenomenon has tail plug audio IC will cause.
We first disassemble the machine, without buckling the tail plug, to see if it is still headphone mode, without buckling the tail plug, or the same headphone mode, it does not seem to be a tail plug problem.
Next, disassemble the machine, remove the motherboard, remove the U0900 audio IC and replace a new audio IC.
Installed test, external playback to restore normal, headphone mode lift, normal function, maintenance to the end of this. This fault is caused by audio IC damage is not inserted into the headset, playback external audio display headphone mode.
Machine model: iPhone 6P
Fault phenomenon: weak WiFi signal, sometimes no WiFi
Failure analysis: rule out antenna problems, remove the chip to see if it is a virtual solder.
The signal is weak, remove the chip to find the 45 pin drop point, this point is just the 2G signal input of WIFI.
Repair point fly line.
Solder on the chip, installed test function all normal, fault repair!
Faulty model】：iPhone 7
Fault phenomenon: No 4G letter on water inserted card
The phone is in the water, the plug-in card has a 2G signal, no 4G signal.
The phone can be on 2G signal, not on 4G signal, indicating that the 4G signal part of the problem, the phone is water before this fault, then water parts in the 4G signal channel caused by.
Mobile phone disassembled, take off the motherboard, microscope observation, observation is not out, remove the 4G amplifier chip.
Remove the TDDPA_RF 4G amplifier chip, measure the ground resistance of the pad, found that the 11 pin MLB_PA_VBATT to ground infinity, it seems to break the line.
View the circuit diagram, found that this voltage to TDDPA_RF, MLBPA_RF 2 chip, MLBPA_RF this chip is not installed.
This voltage is PP_PA_VBATT through R7113_RF resistor renamed MLB_PA_VBATT, microscope observation, found that R7113_RF resistor has been corroded.
Check the circuit diagram labeled as 0 ohm resistor, directly shorted it.
Put the chip back on, install the machine test.
Test 4G signal back to normal, water caused by 4G amplifier power supply is insufficient, caused by no 4G signal, to the end of this repair.
Faulty model: iPhone 6 Plus
Fault description: automatic restart from time to time
According to the customer’s description, the machine is faulty for irregular automatic restart. Connected to the ammeter charging, found that the current is 0.05A, basically no current, is not charging.
At first, I thought it was USB and charge management chip problem, first disassemble the motherboard, and connect the USB management chip and charge management chip around. The capacitors, resistors hit the ground value, and found that the ground value are normal. Then measure the tail plug whether there is a 5V power supply output, 5V power supply is also normal.
Customers since the restoration of factory settings, the first brush in the boot test, boot, prompt does not support this accessory, and let me boot suspected Is not USB bad, test and online video and other functions are normal, no reboot. Pick up the machine first to open the screen a split second, suddenly reboot, is the battery holder contact bad? Quickly look under the microscope, scrape a bit of the test foot copper with a pair of tweezers, then load the battery and turn it on.
After an afternoon test, no reboot phenomenon found again, the fault is perfectly eliminated.
Fault phenomenon] The phone screen is half light and half dark, yin and yang screen
Customer an Apple 6, the fault description says it is not on. With an adjustable power supply, power on 30-60-100-120, the current is normal, careful observation of the motherboard, should not be repaired. Measure to show seat J2019, measure each foot to ground value, 26th foot 0l, infinity, and check further down. fl2037 broken wire, measuring resistance, the tip of the nib touched and fell off, the original is this inductor virtual solder, immediately re-soldered. XinZhiZuo software in the iPhone 6 point map, as follows.
And then power on the test, yin and yang screen.
Yin and Yang screen many are backlight circuit caused by burned-out backlight circuit components, generally as long as the circuit in the burned-out components for a solution.
Play display seat resistance, found 2 feet backlight circuit 1 broken line, will FL2025 inductor short, resistance value is normal.
Hit the display seat resistance value again, all normal, power on the machine test.
Start-up screen display is normal, test all kinds of normal functions, maintenance to this end.
Faulty model] iPhone 6p 64g
Customer description said the phone external sound, insert headset normal, vibration and answer the phone are normal.
The boot test is indeed the same fault as described by the customer, because plugging in the headset normally represents the working condition of the phone big audio is already met. It could be a problem with the big audio chip and the audio amplifier or the I2S2 (the audio cable for the external amplifier). It could also be caused by the external pairing.
First troubleshoot the external match problem, the phone motherboard removed into our test machine rear shell assembly inside, boot test again found that the original fault. Now you can basically rule out the reasons for external distribution, the target directly aimed at the large audio IC disassembly chip, observe the pad with or without tin and drop point. All normal directly to the material board to remove a large audio IC tin mounted. And then this boot test found that the fault is still the same, now basically rule out the cause of the big audio IC. Disassemble the audio amplifier, measure the corresponding points, found 45_AP_TO_CODEC_XSP_I2S2_, and then remove the audio amplifier. BCLK (I2S2’s clock signal) is disconnected.
This point is only connected to the big audio, audio amplifier and CPU, dismantle the big audio to measure the corresponding point found resistance value is normal, directly from the big audio below to pull a first fly line to the audio amplifier to the corresponding point.
Directly mount the audio amplifier, power on the test.
Power on test, normal external playback, fault repair completed.
Model: iPhone 6s
Fault phenomenon: The CPU on the moving plate drops a little bit.
Moved the board, removed the CPU and found a spot dropped on top of the CPU.
Look at the point map, the dropped point is on the I2C0_AP_SDA bus, scrape the over-hole point next to it on the microscope, tin it, find a line to scrape as thin as possible, blow the wind gun to blow the fly line on the tin, cure the green oil.
Solder the lower layer, power on normal.
Install the upper layer, move the hard drive, baseband, code piece, brush through normally, move the board over!