Oh, my god! My iPhone 6S Plus always keep silence when it is in speaker mode, it just no sound on the iPhone. However, when i plug in the earpiece, the sound is normal. Also, there is no vibration when ringing and recording function is normal. How to fix?
The first step is to judge the fault, if there is no speaker voice when playing music on iPhone, generally the fault is caused by iPhone audio amplifier chips. There are 2 Audio Power Amplifiers: U3700 and U3800.
Which chip is out of problem? The previous test has said that the vibration function is not normal. The vibration function is managed by U3800 chip. Therefore, we remove the U3800 chip to measure the ground resistance of the chip pad. It is found that the E7pin I2S_AP_TO_ARC_MCLK ground resistance is infinitely great.
In WUXINJI schematic diagram, it is known that the signal passes through the R0921 resistance to the iPhone 6s Plus CPU.
In the measurement, it is found that the CPU solder joint is broken down to the R0921 resistance layer. It is not easy to dig the route on the plate layer, so we try to borrow the 12S_AP_TO_CODEC_MCLK signal of the audio IC chip, soldering jumper wire(FX051) from the R0920 resistance to the R0921 resistor.
Now measure it again with Fluke 15B+ Digital Multimeter, the data is normal. In the end, assemble the iPhone, turn it on to test, the sound can be played when it in speaker mode. Also the vibration function is normal now. The iPhone 6S Plus can back to normal work!