How to fix iPhone X rear camera problems

Fault Description:  iPhone X rear camera happens problem after disassembling it.

We got the attached file which described the iPhone rear back camera connector socket happen abnormal. While we have to observe the board carefully under stereo zoom microscope, we notice the board is a little deformed. Seeing the pad, it's a very tricky problem, but we still need to solve the fault.

First, it is urgent for us to process the J3900 rear camera soldering pad, flatten and plaint tin again, next, soldering a jump wire.

Picture 1

Picture 2

After finished welding jump wire, we need to wrap it around one by one, and apply the UV flux oil. One important is that we also need to measure the resistance value by digital multimeter, luckily, it is normal, now we can weld the soldering pad.

Picture 3

Then solder the ball on the jump wire, welding the base. Welding tin to the untouched pin and soldered well. Next, assemble the iPhone X and test, to my surprise, the function of rear camera have recovered normal. The procession of fixing iPhone X rear camera connector socket.
come to end.

Picture 4

How to fix iPhone 6P infinitely reboot after white Apple appears

Fault Description: iPhone 6 Plus reboots infinitely after the while Apple logo appears.

According to our ever experience, the NAND, the Logic EEprom IC may cause this issue, so we need to check the phone motherboard, absolutely we need to disassemble the iPhone 6 Plus.

Measuring the grounding resistance value and power supply for the iPhone CPU, both measured value are normal. Next measuring the working condition of the iPhone Nand flash, it's also normal. When measured the iPhone eeprom IC, we found the bus (AP_TO_EEPROM_I2C) connected to the iPhone logic eeprom IC and the iPhone CPU（VC542） has some problem, the grounding resistance value for one of clock bus is more than 600, but the normal data should be around 400, seems there is a disconnection or the pin of the iPhone CPU is empty-welded.

Pic 1

Because there are only 1 bus has the problem, so we choose to dig the iPhone CPU, so that we can solder the jumper wire. According to check the iPhone schematic diagram via ZXW Dongle, so we can confirm the areas of excavation. Put iPhone motherboard under the Stereo Zoom Microscope, install the new blade to the handle, and then we can start to dig the iPhone CPU.

Pic 2

Dig through the iPhone CPU upper layer , then start to dig the iPhone CPU lower layer, now is the most critical position，we need to be very careful.

Pic 3

Dig off the first layer of ground circuit wire and leak out the circuit wire of the second layer of signal.

Pic 4

Carefully dig out the circuit wire, apply the green UV oil on the extra area, and connect another side to the AP_TO_EEPROM_I2C_SCL pull-up resistor.

Pic 5

Use digital multimeter to measure it again, the grounding resistance value is back to normal. The iPhone 6 Plus can enter the IOS system after booting, the display is normal, which means the failure has been fixed, the repairs are end!

How to fix iPhone 6 no touch fault after dropped

Fault Description:  iPhone 6P can't be turned on after being dropped.

According to the attached file, we found there happens a ineffective touch, we use a replaced screen to test it, but still no works, so we may need to disassemble it.

The bottom of the UMT board is easy to be disconnected, so we plan to dealt with the no- touch fault at first. There are two ways to take the IC: one is to take out with tweezer; the other is to pick up from the side of IC. After removed the iPhone touch IC, reinstalled the machine, and the phone boot White Apple restart, turn on start current run at 300mA.

Picture 1

We haven't repair other place else, only remove the touch IC and check the resistance of the bottom of the board. The resistance is normal after tested by digital multimeter, such problem we haven't meet before. I am a little anxiety see the fallen UMT. Since the start current is too large, take U2 down and look at the starting current, he result is the same without any change. Measure the resistance value of U2 pin habitually.

Picture 2

We found that the PP3.0V on F4 pin is short-circuit, and this line has a large power supply, fingerprint power supply and U5411_RF of the head.

Picture3

Power-up again, we found U5411 - RF heating, disassemble the two components connected with U2, then turn on, we can determine the damage is caused by U5411. Turn on, the iPhone jump from 300mA and White Apple does not enter the system, after replaced U5411, the problem was being resolved. Install the touch IC and test function, occurs a new fault. There is no service after turned on, and no serial number. For this fallen UMT motherboard baseband failure, we remove the baseband CPU directly with QUICK 861DW Rework Station, then the fault will be resolved through welding wire on the left upper left V1, U1.

Picture 4

Finished solder a wire well, then apply UV fluxes oil, re-plant tin on baseband CPU, and installed , finally, test function, all is normal. Repair work finished successfully.

Solve iPhone 7 no service after memory expanding

Fault Description: iPhone 7 happens no service after been expanded to 128.

The first step we do is to brush it into the latest iOS system, we found it can enter the system but no service.

So we need to disassemble the iPhone 7 to check the iPhone motherboard, with the digital multimeter to test the current and voltage,  to measure the power supply capacitors around the iPhone baseband power IC, we found the PP_1V0_SMPS5 is shorted. Generally, this case is caused by a short circuit of the iPhone baseband. Remove the iPhone baseband power, and then measure the PP_1VO_SMPS5 again, it's still shorted.

Pic 1

This is a designed flaw of iPhone 7 Qualcomm version, the iPhone baseband S5 power grounding connect point seems to be disconnected, but not, and it cause iPhone baseband burned.

Pic 2

The solution is put iPhone motherboard under the Trinocular Integrated Microscope, re-connect the S5 grounding connect point, and re-install the iPhone baseband power, borrow a PP1V8_SDRAM on the C3211, pass through a 2.2K resistor to C5701_RF, and then forcibly pull up PP_1V0_SMPS5.

Pic 3

Finally, install the iPhone 7 and test it, now the iPhone signal is normal, the iPhone is working properly.

Solutions for iPhone 6S turn on failure after replacing the card slot

Fault Description:  iPhone 6S happens slot shrapnel is broken and can't read SIM, the peers blew it blind.

While after we checked, we found the card slot is not repair well so that the machine can't be turned on.

The customer said to me that the phone can be turned on but have no display, I feel that this is not the real fault. When power-up, test with digital multi-meter, the current is 100 and have no change, and we start to repair after communicating with the customer.

The iPhone can be online, DFU mode, which should be due to blowing the card slot too over resulted in iPhone NAND flash pseudo-soldering, and there is no brush machine at start.

P1

Disassembling the NAND flash with QUICK 861DW Hot Rework Station, we found a useful electric A5 pin, the point on the NAND flash is big, it will be fine by flying a line from the side capacitor to fill the curing.

P2

The NAND flash tested no problem, reforest tin again, and test the resistance of the bottom board before installing the NAND flash. Install the NAND flash after confirm that there is no problem. Turn on the iPhone, the phone go into the system normally. Next, the we need deal with card slot, it is difficult to remove the card slot, but simple to install. The card slot removal can be opened with several fixed pin through the hot air gun, or the professional stainless steel scissors , clip the outer case gradually.

P3

Since the original card slot have damaged, we can remove it from the discarded board in high temperature. This will ensure the integrity of black glue inside the card slot. When install the slot card aligned pin pressed with the tweezers set. I use low temperature tin, so blow from the front won't affect the NAND flash on the back. After loading the card test, the card read, signal, and call function are normal.

Let us talk about iPhone 6 blurry screen

Got the iPhone 6, while the attached file described the screen is blurry after booting. While we have tried to replace it, but it still keeps the same, so we have to disassemble it to get the phone motherboard.

After removing the iPhone motherboard, we found the upper part is seriously deformed. For the iPhone blurry screen problem, first we need to measure the grounding resistance value of the iPhone display socket J2019 via digital multimeter, the resistance value all is normal. Since the resistance value is normal, next we need to remove the iPhone display IC U1501.

Pic 1

Measuring the grounding resistance value of the iPhone display IC J219, we found the A4 pin is shorted, A4 pin touch 5.7V power supply, it is connected to iPhone black touch IC and some filter capacitors. Because the upper part of iPhone motherboard is deformed seriously, and the iPhone black touch IC is easy to damage, so remove the iPhone black touch IC.

Pic 2

However, it is still short-circuited after remove the iPhone black touch IC, seems it's not the problem of the iPhone black touch IC. Next we need to use QUICK 861DW hot air rework station to remove the filter capacitors that connect to it, after remove the filter capacitor C1577, the resistance value is back to normal. Re-install the iPhone black touch IC and iPhone display IC.

Pic 3

Connect iPhone display screen, and the measure the iPhone 6 with DC power supply, turn it on, the iPhone 6 displays normally. Entering the IOS system, the touch function tested is normal, the repairs end!

Solutions for iPhone 6 no speaker sound

Fault Description: iPhone 6 happens no speakers when answer the call, meanwhile there was no sound when playing music with speaker.

After received the phone, we turn on the power. Then go to Settings - Sounds - Ringtones. Select one from the list. The iPhone 6 has no speaker sound. Everything works fine when you plug in the headphones, which indicates the normal state of the iPhone audio IC. Therefore, the fault may be related to the speaker and audio power amplifier circuitry.

Disassemble the phone and measure the resistance values of 1# and 2# on the flexible cable connector of the charging port. The normal resistance value indicates a normal speaker buzzer.

Continue to measure the resistance between 1#J1817 and ground, 2# with digital multimeter, the value of current is normal, which indicates the circuit from the charging port connector to the U1601 is also normal.

Take out the logic board and check it carefully with LED desktop magnifying Glass, there is no phenomenon of water damage or mold.

Connect the DC power supply to the logic board, measure the power supply voltage of the U1601. The voltage is below 500 and the voltage is abnormal.

Connect the logic board PCB bracket. Use QUICK 861DW hot rework station to remove the U1601.

Test the resistance between A6# of U1601 and ground. the value is normal. Measure the resistance between A2# and ground, the measured value is "OL", A2# and B2# of U1601 are connected to the positive pole of the battery through L1604. So we judge L1604 is the fault part.

Replace the new L1604. Remove the L1604, we can see that one of the pins of L1604 has been oxidized and cannot be tinned. Apply some BGA solder paste to the pads, use heat gun to weld the new L1604. After that, measure the resistance between A2# and ground again, the resisstant value is normal.

Finally, we need to re-solder the chip U1601. Before soldering chip, clean the dirty on the separated U1601. Apply some BGA solder paste to the pads. Place the U1601 to the correct position and solder with heat gun.
Assemble the iPhone. Go to Settings > Sound > Ring. At this time the sound is output normally. The problem of iPhone 6 has no speaker sound have been cleared.

How to fix iPhone 6S turn on failure

Fault Description:  iPhone 6S won't turn on after water damaged. 

After we received it, we use the opening pry tools to disassemble it, and try to power it on,  while we need to take out the iPhone motherboard to check whether it has a short circuit faults. Before that, the water area of iPhone motherboard should be cleaned up.

After observing the iPhone motherboard, we found the upper of the iPhone CPU is deformed, measure it with digital multimeter, the iPhone CPU upper doesn't shorted.

Connect iPhone motherboard to the DC power supply, the stand-by current is about 0.24A. Measure the diode data of PP_VCC_MAIN, the data tested is lower than the normal value。

Put iPhone motherboard under the Trinocular Integrated Microscope to check, we found the capacitor next to the iPhone WIFI IC was seriously blackened. Open the WUXINJI Dongle to check iPhone schematic diagram, so we can know the physical position on the iPhone motherboard.

Pic 1

Remove it directly, and then measure it again, now the data tested has more than 100, and the stand-by current tested also is more than 100mA.

Carefully observe the iPhone motherboard again, we found that there is a capacitor next to the iPhone audio IC also was seriously blackened. Remove it directly, and then measure it again, now the data for PP_VCC_MAIN is more than 300, and the stand-by current turns to 30mA, but the upper part of the iPhone motherboard is slightly hot.

Use rosin method to find out the faulty part, we found the temperature of the iPhone display power part is higher than others. Use QUICK 861DW rework station to remove this iPhone display power IC, and then connect iPhone motherboard to the DC power supply to measure it, now the stand-by current is back to normal.

Pic 2

Install the new iPhone display power IC, and then assemble the iPhone 6S. Test it, now the iPhone 6S can be turned on successfully.

How to fix iPhone 7 turn on failure

Fault Description: iPhone 7 happens broken seriously and caused to cannot be turned on.

Meanwhile, during we check it, we found that the screw posts fell off. But we check the current, which shows the motherboard works well, so we need to check other place.

First, try to power up, we found a large current leakage, and continue to test by digital multimeter , we know the 3V power supply short circuit. Observe seriously, the motherboard card slot position is bent, and the short circuit may be in this position. Remove the two capacitors next to the NAND flash by QUICK 861DW Hot Air Rework Station and power on, the phone turn on normally.

 Test function after turned on, we found no Wifi, sometimes stuck when enter the settings. When check, the Wifi clock signal R0807 end has 1.8V, the other end through the Wifi module 17 pin have no voltage, we replace the resistor, but the fault remains. Remove the iPhone Wifi IC, the soldering pad drop the point.

Originally, we plan to turn on phone without install the Wifi module,  and test its function. But there is leakage when power-up, we have to apply rosin. After removing the heating capacitor and test, the setting function is normal, no longer stuck, next install the WiFi module.

After the installation, test again, WiFi appears, and the problem of stuck setting have been solved, but sometimes appeared restart. Considering that the middle position of the motherboard occues bent, the iPhone Audio IC will cause a restart phenomenon, so we have to disassemble the audio. After replanted fly line, all functions tested normal. The next step is to change the match.

Replace the iPhone fingerprint flex cable on the phone. Then install the repaired motherboard, test function after turned on, all function recovers normal, phone fault repair end.

Solutions for iPhone 6S Plus No Service

Fault Description:  iPhone 6S Plus happens no service when insert the SIM card.

While the attached file described it is possible to be caused by the WiFi failure,  cause he did the repair work before by himself. Meanwhile, we have tried to insert the SIM card, it is true like he said.

So here comes the question, we need to continue the testing. Following the test process.

Continue testing, the signal is normal when you turn on 4G in Cellular Data, it can connect to the 4G network. It's normal to make phone calls and browse the Web，but the signal is bad. Turn off 4G, and then choose 3G and 2G, both of them are showed no service.

The 4G signal can be searched normally, but 2G and 3G are no service, we suspected that the fault should be an iPhone antenna switch or a 2G amplifier.

Is it an error in the antenna switch frequency selection? We decided to replace the antenna switch and test it. After remove the antenna switch, use digital multimeter to measure the diode data, we found the 21th PP_2V8_LD014 power supply of the ULASM_FR antenna switch is grounding short-circuited.

Open the WUXINJI Dongle to check the iPhone schematic diagram, we found the PP_2V8_LDO14 is connected to many places, one of them was sent to the filter U_VOX_RF next to the iPhone WIFI IC.

Measuring the diode data for all the power supply of filter, we found there are several power supply circuit are short-circuited.

According to the description of the customer, we judged that the fault is that the tin ball of the filter next to the iPhone WIFI IC was burned when he repairing the iPhone WIFI IC.

Use QUICK 861DW hot air rework station and Titanium Alloy Tweezers to remove the U_VOX_RF directly，and then turn on iPhone to test, now the 2G, 3G and 4G signal can be searched normally, and the signal tested is normal.

After re-installing the U_VIX_RF, all functions are normal, the repairs end!

Wiser Mind for iPhone 6 Flickering Issues

The next one, iPhone 6, it is a perfect machine, at least i think so, while i have used many models iPhone, but i like this one, only.

Anyway,  as a phone repair shop, we need to fix everything we need on phone problems. According to the attached file, we know there happens a flickered faults, so we need to disassemble it and check the IC.

Well, we need to test it again. Connect to the DC power supply, the screen flickering as before described. According to past maintenance experience, the problem of iPhone multi-touch usually resulted from signal interference or unstable touch screen IC power supply.

Use Fluke digital multimeter  to test the power of PN5V7_SAGE_AVDDN, PP5V7_SAGE_AVDDH, PP5V1_GRAPE_VDDH on the touch screen controller IC and touch screen processor IC, the voltage is normal.

Then we measure the diode value between the coupling capacitance of the touch screen control U2401 and the touch screen control IC U2402 . It is still normal.

Judging from the customer's description, we conclude that the fault may be related to the replaced touch screen IC itself. According to our experience, touch diseases caused by the touch screen controller IC will cause the touch to not work.

Although a faulty touch screen processor IC will only result in a partial unresponsive touch. Therefore the touch processor may be the faulty part. We remove the touch screen processor IC with YH898D soldering station and replace the new one.

To our surprise, when we test the iPhone after the replacement, the fault still exists. We guess that there is only one type of interference that can cause such touch of the disease - some kind of high frequency signal. The NFC IC next to the touch screen processor is most likely because the high frequency signal it outputs interrupts the normal operation of the touch screen IC.

Next step is to replace and test with the new NFC IC. Great, the fault is cleared thoroughly.

Solutions for iPhone X 4013 Errors

While iPhone X has been out of warranty, we have received more and more iPhone X. Today, we will talk about how to fix iPhone X 4013 errors after water damaged.

The first step we need to do is to restore the data, then we boot it normally, but we found there reports an unknown error 4013, same with the file description. 

So we have to quit it and use the professional tools to disassemble the iPhone, and connect it to DC power supply to check the iPhone current. The iPhone X can enter the IOS system when the iPhone screen isn't connected, and the iPhone can be turned on smoothly when the front receiver flex cable isn't connected. 

Observe the iPhone display screen under the Stereo Zoom Microscope, we found the iPhone receiver has the trace of the water.

Remove the front receiver sensor flex cable, we found the photosensitive lens also has the traces of corrosion. Use QUICK 861DW rework station to separate the light sensor, the solder pad has been corroded.

Handling the corroded solder pad, apply the tin, and use green UV oil to cover the area where the copper is leaking, and then install the light sensor back to the solder pad.

Assemble the iPhone and test it, the iPhone is turned on successfully, and it can enter the IOS system properly, the functions tested are normal, the light sensor is normal, the Face ID is normal. 

Summary: this failure is caused by the short circuit of the corroded iPhone X front receiver light sensor, and then caused iTunes unknown 4013.

How to fix iPhone 6P Wi-Fi turn on failure

The iPhone 6 Plus WIFI switch won't turn on after dropping, which means the iPhone WIFI function can't be used, we need to repair it.

Power on iPhone 6 Plus, get into IOS to test iPhone, all function works good, except iPhone WIFI, the iPhone WIFI icon can't be turned on.

First, use phone opening tools to disassemble the iPhone 6 Plus, remove the iPhone display assembly, disconnect the iPhone battery, and then take out the iPhone motherboard.

Put iPhone motherboard under the Stereo Zoom Microscope to observe, we found the iPhone WIFI IC has some problem.

Use QUICK 861DW hot air rework station to heat the iPhone WIFI IC, and then use tweezers to remove the iPhone WIFI IC, there are 18 pieces pin are missing, one of them is an empty pin, no need to fill.

Clean up the solder pad, and then use fill the missing pins, apply some green UV oil to those pins, use UV lamp light to solidify them.

Pic 1

Now, install the iPhone WIFI IC to the iPhone motherboard, and then assemble the iPhone motherboard.

Finally, power on iPhone, test the iPhone WIFI function, the iPhone 6 Plus WIFI switch is turning on smoothly and the iPhone WIFI function works perfectly.

How to fix iPhone 7P turn on failure

Fault Description: iPhone 7P can't be turned on while the charging current shows 200 mA

We disassemble the battery, use the latest iPower DC power supply cable to detect the charging current, but we found it still keeps jumping, connect to the LCD screen, no any display shows.

Next, disassemble the machine and connect DC Power Supply, we find no current. There is no leakage on the front side, triggering a large current, which reaches 1.9A. Then, it’s easy to spray rosin to power on, current appeared.

Picture 1

When we saw this, we all feel frustrated. Does the main power supply has failed? We decide to open the circuit diagram. And open the hot spot, we find there is the NAND flash power supply. Test whether there is a short circuit in the NAND flash! Without surprise, the fault from here after testing with digital multimeter. Because the 6s machine has many problems, what can we referred to is NAND flash at first. Click a few points, we thought this point probably have fault, and measured it, it is the fault one.

Picture2

The next step is simple. Use the iphone Scraper to remove the power supply capacitors around the NAND flash. Plaster on rosin, adjust the current meter to 3V and operate directly.

Picture 3

We found this capacitor shorted and use the crowbar to open it.

Picture 4

Then test it ,we found that there is no short circuit.Turn on and test the battery's electric light is shine. Put it on the activation board and add some power, then turn it on again.

Picture 5

There should be no problem here, we should notice: it is not necessarily that the hot one fault. I think that many people will move the main power supply when repair this iphone. But my advice is to check the circuit diagram with WUXINJI Dongle  to test if the power supply is short-circuited. Such short-circuits outside often occur. Many of the first pictures are short-circuited by the main power supply itself.

How to fix iPhone 8 no boot fault

Fault Description: iPhone 8 can't boot though it is showed power on

After we got this phone, we use the DC power supply to charge it, but we found that the current is 250mA when the iphone 8 is powered on, then goes back to 0 and continues to cycle. Based on past repair experience, we judged that it is related to the USB charging part.

The way to disassemble iphone 8 is similar to the 7th generation. Using the HYT 888D ESD digital desoldering station to disassemble the motherboard, we found that the counterparts have soldered the charging part, while the 8th generation U2 (6300) is still located at the bottom right of the NAND flash, which is not common with previous models. 

Picture 1

Picture2

Remove the U2 with desoldering tool, and use Fluke digital multimeter (VC712) to measure the pad resistance, there is no any abnormality. when the machine powered-on, the current is also normal without U2. Replace the new iphone U2 chip and test machine, we found that iphone can enter the system. And then insert the charger, iphone can not trigger the boot, and can not charge too.

After we replaced the iphone 8 tail plug flexible cable, the problem still existed. Then we measured that the 5V power supply from the charger, which was different from that of the previous generation. There is no Q protection tube, and the tail plug is directly sent to the U3300 charging tube.

Picture 3

We use the digital multimeter measure the voltage has been sent to C3301. Is it because the faulty charging tube resulted in no voltage output? We have to remove the U3300 charging tube and measure the foot with normal resistance. The U3300 chip is also different from previous models. Replace the new iphone 8 IC and test the current have recovered normal when power-on. There is a voltage of 4.2V on the electronic carrier, and the retesting machine is restored to normal. 

Summary

The fault that this iphone 8 can not boot is caused by the charging part. When we encounter an iphone with a charging fault, we could eliminate the external distribution at first and then test the line to judge the cause of the fault.

Way for figure out iPhone 6 Wi-Fi issues

Fault Description: iPhone 6 Wi-Fi can't be turned on while displays grey.

Possibility Reason:  The Wifi IC happens something abnormal.

We have tested the Wi-Fi, it really doesn't work, so the ICs may happens what we have doubted like that.

For this problem, first we can replace the iPhone WIFI IC directly. After install the iPhone WIFI IC, turn on iPhone 6, but it stuck when it entering the Settings, so the problem isn't been solved. Next remove the iPhone WIFI IC and test several key point signals, we found the 14 pin doesn't has the resistance value. Now, we need to check iPhone CPU, it's complicated.

Pic 1

There is no Bus reset signal, the normal is 1.8V, we are going to borrow it from another place, and there is a 1.8V beside it.

Pic 2

It's useless if we directly connect it, so we need to find a resistor to pull it up. Put iPhone motherboard under the Stereo Zoom Microscope, and then remove a boot signal pull-up resistor 220K,

Pic 3

Install the iPhone WIFI IC, and then turn on the iPhone to test, now the iPhone WIFI function can be used normally.

Solutions for iPhone 7 Wi-Fi issues

Fault Description: iPhone 7 Wi-Fi, bluetooth can't be opened.

Possibility Reason:  According to the customer said, he found there exist leakage. And we confirmed that, meanwhile we found the backlight happens something wrong.

Usually, we will judge the damage of general function module will lead to leakage and rapid power consumption. Since the Wifi function cannot be activated, it may be caused by the damage of iphone Wifi IC.

Picture 1

First, disassemble the iphone,  use DC Power supply  to power on, indicates that the current is missing, trigger more than 100 jumps. Then open the motherboard with QUICK 861DW Hot Air Rework Station  we discover it is a water machine, but before that, the customer didn't tell us .

Observe the iPhone under stereo zoom microscope and see that there is corrosion next to the Wifi. Maybe this is where the fault lies.

Picture 2

Clean corroded area with wash water, and remove corroded filter capacitor, then connected to DPS DC power supply, the current starts to jump from 100 hops. So the problem still exist. We check other places and found a small capacitor under the compass that was corroded and damaged. Use digital multimeter to measure the voltage, there is a short circuit condition. Is this the reason of error?

Picture 3

Remove the capacitor directly, measure the resistance value with a digital multimeter, and the resistance value is normal. It is also right after power-on. Install the motherboard and test, Wifi can be turned on, and the compass is back to normal. So dark backlight is due to screen. Fault have been removed, this repair work is over!

Wiser mind for iPad 5 NAND Repair

While the customer said, the iPad happens error 40, at the same time, it can't be turned on. 

Usually we will check the circuit board, so it is necessary to disassemble it, check the iPad motherboard.

First step, we need to connect it with the DC Power Supply, trigger it to test the current, the current stuck in around 40mA. Connect iPad to the computer and DFU restore it, it reports error 40. After entering the restore mode, we found the SN can't be identified.

According to the error code, we judged that it's the problem of iPad Nand flash or the circuit of the iPad Nand flash. Disassemble the iPad 5, take out the iPad motherboard, we found the iPad Nand flash has the trace of disassembling. Measuring the 1.8 and 3.3V of the iPad Nand flash, both doesn't have the power supply.

Check iPad schematic diagram via WUXINJI Dongle, we can know that power supply for both sets of circuits is converted from U3850.

Because the iPad Nand flash was disassembled, so we suspected that the power supply tube was virtual welding. Re-install it, the power supply is back to normal, but the iPad still won't turn on.

Now we need to use Quick 861DW hot air reworks station to remove the iPad Nand flash, after remove the iPad Nand flash, we found some pins of the solder pad are missing.

Pic 1

Refill the solder pad, installing the iPad Nand flash to the iPad motherboard. Assemble the iPad and test it, now the iPad is turning on smoothly, the repairs end!