As we all know, when supplying the short-circuited logic board with power, faulty components on it will get hot. For logic board bearing significant fever, we can locate the faulty component quickly and precisely with 'rosin detecting' method.For more detailed application, check our video today and we will show you how to fix iPhone 7 Plus won't turn on after water damage issue with 'rosin detecting'.
iPhone won't turn on repair list:
iPhone 7 plus won't turn on
First, run cosmetic inspection of the logic board, the logic board is not deformed. Yet areas around the WiFi module bear obvious signs of water damage, and we can see clearly that the water damage indicator is red.
First, let’s clean moldy area on the logic board with PCB Cleaner
Then, connect the logic board with the Power Supplier, and press power button on the Power Supplier to power on. Current reading on the ammeter is larger than normal value, Judging by the current reading on the ammeter, one rail of power supply of the logic board might have been short-circuited.
Run diode mode measurement of the two rails of main power supply PP_BATT_VCC and PP_VDD_MAIN first. Judging by the measured value, the two are in normal condition.
Next, we need to check several rails of power supply outputted from PMU, run diode mode measurement of capacitors on these power supply circuits. The measured value of C2302 and C2308 on PP_VDD_BOOST is 0, which is abnormal. So PP_VDD_BOOST has been short-circuited to ground. There are multiple associated components on PP_VDD_BOOST, PMU U1801, U3101, U2501, U3001, U3702 and several filter capacitors.
Since there are so many components on the circuit, we can confirm the fault component with ‘rosin detecting’. Dip some rosin with Soldering Iron, and smoke rosin on relevant components.
Then, connect the two test leads of the Multimeter with DC Power Supply, set voltage of the DC Power Supply to 3V, get the black lead grounded, meanwhile, get the red lead touched with Pin 1 of C2308, rosin on C3002 melts immediately.
Judging by this, the short-circuited condition is caused by damage of C3002. Since C3002 is a filter capacitor, we can fix the problem by detaching it from the board.
Remove C3002 with Hot Air Gun, wait for the logic board to cool for 5 minutes, then clean with PCB Cleaner afterward. Continue to run diode mode measurement of C2308, the measured value is normal.
Then connect the logic board with the Power Supplier and press power button on the Power Supplier to power on. Current reading on the ammeter is normal this time.
Now we can assemble the phone and test, get the logic board and display assembly installed, connect the battery and press power button, the phone turns on normally, fault cleared.
Warm tips: get the phone full assembled after confirmation of fault clearance.
The above is the detailed steps of iPhone 7 Plus won't turn on repair - find the faulty component with rosin. Is it hard to understand or feel not clearly? Don't worry, we also have the video for it. Click to watch the video below. Any questions or suggestions please don't hesitate to tell us by comment below or ask a question on ASK Forum. REWA will try to answer you in time.
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Apr 23, 2021
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