How to repair a volume button fault effectively?

Once one of phone part was used frequently, maybe it will cause a fault, So can i ask a question which part was used mostly in most smartphone?

Like the topic said, the volume button, when you listen music, making call with your family or watching some video, you will use it. So there exist a great possibility to happen fault on this button.

Today, what we will repair is the phone volume video fault, the up button has no reply while the down button runs normally, so maybe one of them happens IC control fault, anyway, we need to confirm it.

Firstly, we need to check the  iPhone volume button, we found the volume down button runs normally while the up button has no response, so we have to contrast diode data to check it.

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:

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.

Assemble the volume button, then check it, we can turn the music sound freely, it shows the repair result was succeed.