Test the other functions on the iPhone, they all works well, the receiver and the recording function is normal. After restarting the iPhone 6 Plus, the problem is still the same, is it the iPhone hardware problem? As we know, the iPhone speaker problem generally is related to the iPhone Audio IC and iPhone small audio IC.
Sign in to the ZXW online account to check iPhone schematic diagram, according to the iPhone speaker working principle, the speaker is connected to RF IC by iPhone tail plug flex cable.
In order to confirm that whether the circuit between the iPhone tail plug interface and the iPhone small audio IC is correct，we need to use Fluke 17B+ Digital Multimeter to measure the diode data of 31 Pin, 32 Pin, 33 Pin and 34 Pin, which connected to the iPhone tail plug interface J1817 and iPhone speaker.
Next we need to check iPhone audio amplifier working condition, and whether the I2C1 and I2S2 bus of the communication circuit from the audio amplifier to the CPU and main audio chip normal or not.
Use QUICK 861DW hot air rework station to remove the iPhone audio amplifier, and then use digital multimeter to measure the diode data of the solder pad that to the CPU signal circuit and I2C1 bus. After measurement, the diode data of I2CI bus is normal, which means the PCU and I2CI signal circuit of the audio amplifier are good.
Continue to measure diode data of I2C2 bus, it’s found that the data of E7 Pin AP_TO_SPKAMP_I2S2_MCLK cable is infinite. Check iPhone schematic diagram, we know that there is a resistor R0311 between pin E7 and CPU. Measure the diode data of its ends, the data is infinite. Now we know that the circuits in CPU disconnect or CPU is pseudo soldering.
Check schematic diagram again and find that I2S2 bus is also connected to large audio chip. However, the signal AP_TO_SPKAMP_I2S2_MCLK is not connected to large audio chip which uses signal AP_TO_CODEC_I2S0_MCLK, and this signal passes a resistor R0301.
Use Quick TS1200A soldering station to solder a jump wire form R0301 near CPU to resistor R0301 near CPU, sharing the AP_TO_CODEC_I2S0_MCLK signal of the main audio.
I hope your iPhone ia all well. If you have other iPhone-related questions, please leave a message in the comments.