Since direct access to proprietary manufacturer schematics (which are protected intellectual property) is restricted, I have compiled a technical paper that deconstructs the .
When viewing the schematic PDF, look for these specific sub-circuits:
: Jumper solutions for the Power On/Off and Volume buttons. Where to Download OPPO A15 Schematics (PDF)
Schematic paths for the main microphone, speaker amplifier, and the triple-lens rear camera setup. Troubleshooting with Schematics