The colleague send an iPhone 6S Plus to us, the fault described is that the iPhone was dropped, the screen is blurred when iPhone is turned on, the colleague feedback that after replace iPhone display touch boost IC, the iPhone display screen back to normal. However, when they test iPhone, the iPhone volume button doesn’t respond.
Now, we need to test iPhone again. Press the iPhone volume button, we found the volume up button has no response, the volume down button and mute button is normal, contrast diode data to see whether normal. The picture as follows
The J4701 socket fourth pin is volume up button, measure its diode data with Fluke 15B+ Digital Multimeter, the data is normal, check its voltage, it only has 0.3V, while the normal voltage should be 1.8V. The voltage was pulled down, considering whether is caused by load leakage on the path.
Check iPhone schematic diagram on WUXINJI Dongle, we know that the load on this circuit has capacitor C4713 and diode DZ4713. If these two components leaks, it will cause this circuit voltage is pulled down. Remove these two components, and the voltage measured still is 0.3V.
According to the iPhone schematic diagram, we know that this circuit doesn’t have a pull resistor, which means that the pull voltage is done through the internal CPU. Measure the diode data again, the data is normal, which means the iPhone CPU doesn’t have a virtual weld, it is caused by local damage.
Use the method that borrow the voltage from other circuit, modify a 1.8V pull voltage on the volume button. Based on bitmap to find the most recent circuit can be used to borrow voltage, the picture of the modified circuit is as follows:
With the help of QUICK 861DW hot air rework station, borrow a 1.8V voltage from compass power supply, and connect a 1KΩ resistor on capacitor C3000 1.8V end to capacitor C4713 non-earthing end. And then measure the fourth pin on J4701, it has 1.79V voltage.
Install the iPhone and test it, the volume button is now working properly.